Grimstuff's Scratch Build Journal (building, casting, painting)
- Thread starter Grimstuff
- Start date
ToEleven
Active Hunter
If you look at the ESB helmet photos in the archives you'll see this. The left mandible sits a little higher. Probably the result of the damage/repair that also caused the crack and wavy brow. The helmets in general are all a little asymmetrical...the ESB even more so.
Sent from my XT1585
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Grimstuff
Active Hunter
Awesome, good to know that's all how it's supposed to be. Early on I took a few broad measurements here and there just to make sure my template print was sized correctly, but for most all the smaller asymmetries and stuff I pretty much just left my trust in Rafelfett's templates. My big fear was if anything got warped during the heat forming or other parts of the early construction.
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tk675
Hunter
Yup. It's me. Haha...I just looked at my helm and the pics and they don't line up exactly. Carry on with the awesome work. I shall watch quietly from now on.
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ToEleven
Active Hunter
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RichardJones
Active Hunter
Wow your dent is looking a million times better! I can't wait to see one of these painted up.
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Grimstuff
Active Hunter
Ayy I'm back, with quite a lot done.
I was hoping to do some quick little live updates throughout the whole molding process, but I kind of got immersed in the work I guess, because it's pretty much all done
I suppose I'll just try to cover it with some more write-ups then.
Silicone Molding Planning
Supplies
And here's the essentials to doing something like this.
In no particular order that matches the image:
I was hoping to do some quick little live updates throughout the whole molding process, but I kind of got immersed in the work I guess, because it's pretty much all done
I suppose I'll just try to cover it with some more write-ups then.
Silicone Molding Planning
So with my master all done and primed and met with the approval of you guys, we come to the molding and casting process.
I had done quite a few molds before, but not for an object as large as this, so I began by researching into some advanced mold making techniques. What I gathered was that there's two main ways to economically make a mold of something like this: matrix molding and brush-on molding.
I had done quite a few molds before, but not for an object as large as this, so I began by researching into some advanced mold making techniques. What I gathered was that there's two main ways to economically make a mold of something like this: matrix molding and brush-on molding.
Matrix Molding vs Brush-on
Matrix molding consists of covering the entire project in a temporary inner-mold material such as clay that you then surround in an outer support shell, with the goal being to eventually remove the clay and then pour silicone into where it used to exist. Brush-on molding on the other hand skips the temporary material entirely and has you instead brush silicone directly onto the project, which you then encase in the support shell.
Now matrix molding can give some really professional as hell looking molds, but it's generally quite a bit more costly due to it often being a much thicker and sturdier of a mold; meaning more silicone is used. One of the big benefits though is that you can easily just use regular 'ol pour silicone with it (brush on requires special higher-viscosity silicones), which is one reason I suspect why many big studios with lots of bulk supplies usually use the method.
Since I'm buying materials specifically for this job though, and I'd like to keep things as cheap as possible, I elected to go ahead with the brush-on method. This means I'm going to need a specialty brushable silicone, material for a support shell, and some plastic to actually cast into it when all is done. So I started on my shopping list and got the wallet out.Now matrix molding can give some really professional as hell looking molds, but it's generally quite a bit more costly due to it often being a much thicker and sturdier of a mold; meaning more silicone is used. One of the big benefits though is that you can easily just use regular 'ol pour silicone with it (brush on requires special higher-viscosity silicones), which is one reason I suspect why many big studios with lots of bulk supplies usually use the method.
Supplies
And here's the essentials to doing something like this.
In no particular order that matches the image:
- Smooth-on Rebound 25 Silicone - 1 gal - $183.72
- Smooth-on Smooth-Cast 321 Polyurethene Resin (off-white) - 1 gal - $82.83
- Smooth-on Thi-Vex Silicone Thickener – Pint - $15.50 (You absolutely don’t need a pint and can just get the 3 dollar 1oz though)
- Smooth-on Silicone Thinner – Pint- $11.93
- Mann Ease Release 200 Releasing Agent – Can - $13.20
- Lots of sulfer-free clay (not pictured) - ~$10
- Fiberglass Resin 1 gal - $37
- Fiberglass Matting (I bought in bulk, but used about 2-3 store sized packages of material) - $30
- Acetone (for cleaning up fiberglass resin messes)
- Chip brushes
- Tongue Depressors
- Gloves (anything works with silicone, but thicker the better when it comes to fiberglass)
- Disposable mixing cups (pref both waxed paper and plastic)
- An electric gram scale (not pictured)
- Aluminum Tape
- Petroleum Jelly (or other material that works as a fiberglass resin release)
- ~1 inch bolts with nuts
- Probably some other items that I've forgotten too and will add here later.
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Grimstuff
Active Hunter
Brush-on Molding Prep
Now that I’ve chosen a molding technique, I have to choose the mold style I want; a single piece glove mold or a two-piece mold.
Glove mold vs 2-part mold
(images taken from Harrison Krix’s fantastic build logs for his Daft Punk Helmets, go check em out)
(images taken from Harrison Krix’s fantastic build logs for his Daft Punk Helmets, go check em out)
Glove molds are advantageous in that since it’s all one continuous piece of rubber, there’s no parting lines or flashing to worry about in your casting, they come out incredibly clean and ready to go. The big disadvantage though, and where 2-part molds are better, is the difficulty of actually removing the cast item from the mold after it’s cured. A complex master with many recesses and other geometries create mechanical locks which are difficult to remove from a 1-piece glove mold, usually requiring a lot of stretching and stressing to the rubber which can shorten it's shelf life significantly.
Since the Fett helmet has quite a few features that could create mechanical locking, I chose a two-part mold for this project. The parting line will be an annoyance, but with the big flat surfaces of where I plan to place it, it should be very easy to sand or file out.
Parting Line and Claywall
The process of starting a 2-part mold is essentially to find a good parting line that will exist between the two halves of the mold. More or less the goal here is to create two sides that will individually experience the least amount of mechanical locking possible. Additionally, since it’s impossible to perfectly align the two halves again later, the resulting seam will be visible in the cast plastic, so it’s important to think about how difficult it will be to remove it. If possible, try to place it in segments that will be cut out later or just less-visible.
For the fett helmet, I definitely knew I didn’t want my parting line running across either of the ears, as it would be quite hard to remove that. This lead me to choose a front-to-back line, which as a bonus places a big chunk of the line on the visor, which will be cutout later.
The only complication though is the keyhole slots on the back. Just as with the ears I knew I didn’t want my parting line passing over these as sanding this area is a huge pain. So I chose to angle off a bit away from it. I was a bit worried this might create some complications with the mother molding process later on, but I figured I’d cross that bridge when I get there (spoiler though: it worked fine).
After you’ve determined where your line will be, you'll begin creating a wall that will keep the first half of silicone to one side of it. You’re essentially gonna build a dam around the entire circumference of your item. There’s a few materials that can be used for this, but nearly everyone uses plasticine modeling clay because it’s easy to apply and reusable, so I did too. Just make sure it’s sulfur free, as sulfur inhibits silicone curing. Most art clays are fortunately enough though.
I began this process by mixing all my clay up together (about 3 packages worth) into two big giant clumps. Then I took a drywall knife and cut these clumps into a bunch of long rectangles. You’ll need a heat source in order to help make the clay more easily workable, I used a hairdryer but if nothing else you could just keep some warm water on hand too.
I then started applying these long rectangles to the parting line. Because I wanted to make sure I got that forehead band thing covered well I started there.
From then on it was pretty much a process of circumnavigating the whole thing. At the top I had to create my angled off split that I did to avoid the keyholes. Around the base I just had to make another circumnavigation for the entire inside rim. The Fett helmet is a pretty simple open bottom bucket, so I didn’t have to do any inward recesses here or anything complex there, just a simple wall for the silicone to stop at.
After the whole thing was covered, I did some work to clean up the meeting point between the clay and the master. You want this to be as tight and clean and perfectly 90 degrees perpendicular as possible in order to keep the parting line minimal in the castings. I mostly did this with some silicone clay tools and heat application.
After that, I took the opposite end of those tools and created registration keys all along the clay wall. These help with aligning the two silicone halves when they are put back together. Pretty much the only trick with these is not getting them too deep or complex so as they become difficult to mate or separate them, as problems there could actually defeat their entire purpose. I like to do some big holes for the more general lock, then some tinier precision holes closer to the piece to give it a little extra accuracy. I’m not sure if it actually helps any to do it like this, but it looks kinda cool.
That's pretty much the meat of the prepwork done, and where you can begin laying out materials for the silicone funtime.
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Grimstuff
Active Hunter
Brush-on Molding Silicone Application
Alright, so here we finally get to the actual meat of the whole thing, applying some sex rubber.
Brush on molding is a process that’s done in several layers, starting very thin and delicate at first to capture the most detail and prevent bubbles, then getting thicker and more meaty as you go. If you’re wise with your applications of each, 4 layers should be about enough for a good economical mold. One thin layer called the print coat, one normal layer, then two thickened layers to give it some meat. If you’re liberal with your materials, you can do one final thinned 5th coat over all that to make it nice and smooth looking.
Be prepared to set aside an entire day for each half of this though, as you must apply each layer in a Goldilocks moment when the layer before it is still tacky but not fully dry. It takes a little under an hour to reach this point, so that’s at a very minimum 4 hours of work, not including time spent mixing, degassing, and applying the silicone layers themselves. I used the time to catch up on some movies and TV backlog, and also finished the Assaj Ventress audiobook (which was a little ehh imo).
Anywho,
Measuring, Mixing, and Application Overview
How much to buy:
As I put in my supply list, you’re going to need quite a bit of silicone for this, and I bought a full expensive as hell gallon of Rebound 25 because I have some other projects I want to repeat this method on too.
If you’re just going to do one single project though, then you can instead just go with a few of the trial sized containers and save some money. One helmet takes about 1/3 of the full 18 lbs gallon, so about 3 of the 2lb trail sized containers should give you enough to work with. 2 maybe if you’re really economical with your application and make a really good mothermold to keep it stable, but I wouldn’t risk it, better too much than too little. It’s worth considering too that with the trial-sizes, you’re paying half the price of the gallon size for only a third of the material, so if you do plan to do more brush-on projects in the future, it may be more economical to just go for the full thing like I did.
Additionally, if you plan to only take a few pulls of your bucket and don’t expect too much library life out of it, you can go with the cheaper tin-cure silicones too. Smooth-on’s brushable tin-cure is called Mold Max Stroke. The trail sizes aren’t too much cheaper than platinum-cure, but the gallon size though is a whole of a lot cheaper at nearly half the price. Worth considering.
How much to mix:
Depends on the thickness of the layer. For the highly thinned print coat I used about 100ml A + B (so 50ml A then mixed with 50ml B).
For about everything else I generally used something in the ballpark of 200-300ml A + B. I had some run-off with the normal coats though so stay on the lower end for them, and for the thickened coats it’s a little scarce for a complete cover, but I as I’ll go over later I actually applied my thickened coats in a few separate mini-layers so I could better focus it’s application.
All in all, you’re going to use about 600ml per completed side. I pre-transfer about that amount to some secondary containers so that I don't have to constantly keep drawing from the gallon buckets directly.
Degassing:
Pretty much the biggest worry when it comes to molding and casting things is the bubble devil. He loves to insert his evil little blisters into your materials and leave eternal little sigils of annoyance that will forever plague your castings. Luckily though we have one holy force at our disposal to remove him and his effects, the power of vacuum. With this we can suck him right our of our work and enjoy the eternal bliss of a smooth bubble-free mold. It’s for this reason it’s a very good idea to vacuum degas your silicone and urethane whenever possible. You can get by without it if you’re careful and use some anti-bubble techniques, but since we’re dealing with a couple hundred dollars of material here, I think it’s better to get the equipment to do make sure it doesn’t get messed up.
Fortunately you can build a degassing chamber for much cheaper than the pre-made ones that many companies offer. Mine is literally just a big thick stockpot with a thick acrylic lid over it. About a 40-50 dollar project, the more expensive part will be the vacuum pump itself which you can get at harbor freight for about $100 off-sale. Combined this is half the price of the smallest sized commercial vacuum chambers alone, sans-pump. You might be worried about safety, but unlike pressure chambers which are pretty much bombs, vacuum chambers are much safer to DIY as the pressure releases the moment vacuum breaks and if anything does go catastrophically wrong, it’s an implosion rather than an explosion, so the danger is much less. Just don’t use a thin glass container or anything dumb like that.
When degassing, use a mixing container at least double the volume of your material as it will expand a lot. After it expands it will fall back down, and with that most the gas is out of your silicone/urethene, but not always all. I usually let it degass for a full minute or two just to make sure, but don’t overdo it though as you’re eating away valuable pot life.
Application:
I’ll repeat these for each layer, but as a general overview for now you can sort of split your applications into two groups, poured on and spatula’d on. The print coat and the normal coat are both low-viscosity enough to be poured onto the highest point of your master and let to flow down over it with the aid of a brush. The print coat should be spread over via a stippling motion with a brush in order to get complete gentle coverage and prevent the introduction of any air, while as the normal coat can be more safely normally brushed around (don’t be too fierce though or you’ll lift up or otherwise damage the underlying print coat).
If you do get any bubbles in your brushing method, a useful trick you can do is to actually use compressed air to remove them. Using either a compressed air can or an air compressor with a blow tip, blow into the wet silicone in order to push out any bubbles, it sounds sort of counter productive, but what you’re actually doing is compressing and pushing out the bubbles via the force of the air.
Now, the thickened coats are way too thick to do any flowing, so they must be scooped out of the mixing container and manually spread over the sculpture. I use the mixing tool, tongue depressors, for this.
So without further ado, lets start with actually getting these layers on.
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Grimstuff
Active Hunter
Applying the First Side
0 Mold release:
Before anything, mist a nice layer of mold release over your sculpt and the claywall. While not absolutely necessary for the first half, it will be necessary for the 2nd. Since spray release can subtly affect the texture of your castings, just for consistency’s sake it’s good to do it for both. I use Mann Technologies Ease Release 200, but there's a lot of other options out there too, just make sure it's for silicone applications.
Don't over apply, as you don't want it so slippery that your first half of silicone is slipping off as you're trying to apply the second. Just a misting, and focus more on the clay wall than the sculpture.
1 Print Coat:
I actually kind of ****ed up a bit with this one, but fortunately nothing with any lasting impact.
The goal with the print coat, and what I messed up on, is to get a thin skin of silicone covering the entire half of your master. Somewhere in my head though I got focused on getting silicone into all the crevices of the ears and other areas that I knew would be difficult that I sort of abandoned everything else. Getting all that stuff properly filled in is important, but it should be something you do as your next step after your print coat is on. Fortunately I mixed up another batch of silicone and got my proper print coat on before that initial layer even tacked up, so it didn’t really hurt anything in the long run.
I used the 10% mixture of Smooth-on’s silicone thinner for this layer, and applied it by first pouring it over the high points of the sculpture then stippling it around with a chip brush as it flowed down. Much of it will eventually flow down to the claywall, but that’s ok. If there’s so much it’s flowing off completely though, you can scoop some up with the brush and place it back on top or in crevices here and there if you want.
Also.. besides the above mentioned error, there's another big mistake visible here that experienced moldmakers might be able to spot. I'll keep you in suspense of what it is until the closing conclusions part of the post though.
2 Normal Coat:
This is done much similarly to the print coat, but just no thinning agent is used. In it’s default state rebound 25 is still thin enough to still flow somewhat, so do the same pour on top method, but this time feel free to brush it around as needed instead of only carefully stippling. Again, just don’t do it so hard that you damage the tacky print coat underneath it though.
If you see any bubbles from your brushing process, pop em with a needle or use the above mentioned compressed air method to get rid of em.
After this coat, or during it if you mixed enough silicone, take some time to try to get some silicone mass into any holes or crevices that are going to need to be filled later. The thickened coats will be too thick to fill these in. You should focus on things like the ears, the rear keyholes, forehead triangles, the borden connector, and the cheek square.
3-4 Thickened coats:
These are a bit of a lie because I like to break them up into a number of sectional smaller coats. Thickened silicone sort of has the consistency of cake icing, so though it sticks and goes on thickly, trying to shape it well or apply it over itself can be a tricky mess. Doing it in micro-layers adds a lot of extra time to the project, but it makes it easier to work and saves me the risk of mixing up more silicone than I can chew and having it set up in the cup and go to waste.
First things first I do a general covering over the entire thing, this is more or less the full first thickened coat in it’s entirely. After that sets up I do the more advanced second coat, starting with another general covering, then a covering of extruding detail points such as the ears or big crevices such as the rear keyhole, then another final coat to thicken and reinforce the mold wall. By the end of it all you end up with a nice weighty thick silicone shell around your whole piece, with a strong mold wall.
As for the thickening agent; my first coat I tried to go for the 0.5% mix in the technical sheet to try to avoid the creation of too many air pockets, for the second coats I used the really bulky 1% mix. The difference between 0.5% and 1% is pretty hard to differentiate with these relatively small batches of silicone though, so it’s not really too exact a science. Do a little less the first time, then a little more the second.
An additional thing that’s very useful to do during this step is to add some registration keys that will come into play later for the mother mold. Same with the registration keys used to align the two mold halves, these will help anchor the silicone into the mother mold that will encase it. Back during your normal coat, mix up some extra silicone and pour it into some small roundish holes. A painters pallet is perfect for this and what I used. Let these cure past the tacky stage, 2-6 hours, then demold them and ‘glue’ them on while you’re applying one of your thickening coats. Fortunately, if you initially forget to add these... like I did, it's not the end of the world. Silicone sticks to silicone, and even though the bond won't be as strong as gluing them on wet, it'll still hold plenty well.
After that’s all that, let it sit overnight to get a nice full-cure.
Applying the Second Side
Prep:
Now that your first half is all nice and cured up, time to flip it over and remove your clay wall. This will probably be a pain, but it can help to use something to cool the clay some and make it more solid, that way it can pull off in all one continuous chunk with minimal residue.
If you're having any trouble with your first silicone half degloving from your model, you can wrap an elastic around it to help keep it in place. Just don't do anything so tight that it's compressing the silicone.
Mold Release:
Same as above, but give it a lil something extra over the exposed wall of your old 1st layer. Remember, silicone sticks to itself and you absolutely do not want these two halves to perminatly bind. Release agent is the thing that prevents this, so give it a nice light spraypaint-ish coating over and let it dry. Don't over do it though, as too much could inhibit curing or cause other issues. You want it covered, but not soaking.
Coatings:
Pretty much same as before. This time I remembered to do the registration keys beforehand and applied them properly with the tacky thickened layers.
The last shot gives a good example of the reinforcement I give to the mold wall.
After they're all on, let it sit overnight again to get it's full cure.
Conclusions
So with that both sides are done.
After it was fully cured, I went ahead with an exacto knife and cut off the edge of the mold wall to remove all the silicone run-off and expose the line between the two halves. I wouldn't recommend actually separating them yet though, as we still need to do the mothermold and we don't want to risk any fiberglass resin managing to flow into there.
Things that went wrong:
Besides those though, this went pretty well. The mold turned out with zero bubbles or other issues, and has a pretty consistent thickness throughout and didn't use too much material. You can't ask for too much more than that. Next up will be the mother-mold process, which will probably be a much more simple write-up than this was, since it was messy as hell and I didn't take as many photos.
Feel free to comment or share anything about the silicone process in the meantime.
0 Mold release:
Before anything, mist a nice layer of mold release over your sculpt and the claywall. While not absolutely necessary for the first half, it will be necessary for the 2nd. Since spray release can subtly affect the texture of your castings, just for consistency’s sake it’s good to do it for both. I use Mann Technologies Ease Release 200, but there's a lot of other options out there too, just make sure it's for silicone applications.
Don't over apply, as you don't want it so slippery that your first half of silicone is slipping off as you're trying to apply the second. Just a misting, and focus more on the clay wall than the sculpture.
1 Print Coat:
I actually kind of ****ed up a bit with this one, but fortunately nothing with any lasting impact.
The goal with the print coat, and what I messed up on, is to get a thin skin of silicone covering the entire half of your master. Somewhere in my head though I got focused on getting silicone into all the crevices of the ears and other areas that I knew would be difficult that I sort of abandoned everything else. Getting all that stuff properly filled in is important, but it should be something you do as your next step after your print coat is on. Fortunately I mixed up another batch of silicone and got my proper print coat on before that initial layer even tacked up, so it didn’t really hurt anything in the long run.
I used the 10% mixture of Smooth-on’s silicone thinner for this layer, and applied it by first pouring it over the high points of the sculpture then stippling it around with a chip brush as it flowed down. Much of it will eventually flow down to the claywall, but that’s ok. If there’s so much it’s flowing off completely though, you can scoop some up with the brush and place it back on top or in crevices here and there if you want.
Also.. besides the above mentioned error, there's another big mistake visible here that experienced moldmakers might be able to spot. I'll keep you in suspense of what it is until the closing conclusions part of the post though.
2 Normal Coat:
This is done much similarly to the print coat, but just no thinning agent is used. In it’s default state rebound 25 is still thin enough to still flow somewhat, so do the same pour on top method, but this time feel free to brush it around as needed instead of only carefully stippling. Again, just don’t do it so hard that you damage the tacky print coat underneath it though.
If you see any bubbles from your brushing process, pop em with a needle or use the above mentioned compressed air method to get rid of em.
After this coat, or during it if you mixed enough silicone, take some time to try to get some silicone mass into any holes or crevices that are going to need to be filled later. The thickened coats will be too thick to fill these in. You should focus on things like the ears, the rear keyholes, forehead triangles, the borden connector, and the cheek square.
3-4 Thickened coats:
These are a bit of a lie because I like to break them up into a number of sectional smaller coats. Thickened silicone sort of has the consistency of cake icing, so though it sticks and goes on thickly, trying to shape it well or apply it over itself can be a tricky mess. Doing it in micro-layers adds a lot of extra time to the project, but it makes it easier to work and saves me the risk of mixing up more silicone than I can chew and having it set up in the cup and go to waste.
First things first I do a general covering over the entire thing, this is more or less the full first thickened coat in it’s entirely. After that sets up I do the more advanced second coat, starting with another general covering, then a covering of extruding detail points such as the ears or big crevices such as the rear keyhole, then another final coat to thicken and reinforce the mold wall. By the end of it all you end up with a nice weighty thick silicone shell around your whole piece, with a strong mold wall.
As for the thickening agent; my first coat I tried to go for the 0.5% mix in the technical sheet to try to avoid the creation of too many air pockets, for the second coats I used the really bulky 1% mix. The difference between 0.5% and 1% is pretty hard to differentiate with these relatively small batches of silicone though, so it’s not really too exact a science. Do a little less the first time, then a little more the second.
An additional thing that’s very useful to do during this step is to add some registration keys that will come into play later for the mother mold. Same with the registration keys used to align the two mold halves, these will help anchor the silicone into the mother mold that will encase it. Back during your normal coat, mix up some extra silicone and pour it into some small roundish holes. A painters pallet is perfect for this and what I used. Let these cure past the tacky stage, 2-6 hours, then demold them and ‘glue’ them on while you’re applying one of your thickening coats. Fortunately, if you initially forget to add these... like I did, it's not the end of the world. Silicone sticks to silicone, and even though the bond won't be as strong as gluing them on wet, it'll still hold plenty well.
After that’s all that, let it sit overnight to get a nice full-cure.
Applying the Second Side
Prep:
Now that your first half is all nice and cured up, time to flip it over and remove your clay wall. This will probably be a pain, but it can help to use something to cool the clay some and make it more solid, that way it can pull off in all one continuous chunk with minimal residue.
If you're having any trouble with your first silicone half degloving from your model, you can wrap an elastic around it to help keep it in place. Just don't do anything so tight that it's compressing the silicone.
Mold Release:
Same as above, but give it a lil something extra over the exposed wall of your old 1st layer. Remember, silicone sticks to itself and you absolutely do not want these two halves to perminatly bind. Release agent is the thing that prevents this, so give it a nice light spraypaint-ish coating over and let it dry. Don't over do it though, as too much could inhibit curing or cause other issues. You want it covered, but not soaking.
Coatings:
Pretty much same as before. This time I remembered to do the registration keys beforehand and applied them properly with the tacky thickened layers.
The last shot gives a good example of the reinforcement I give to the mold wall.
After they're all on, let it sit overnight again to get it's full cure.
Conclusions
So with that both sides are done.
After it was fully cured, I went ahead with an exacto knife and cut off the edge of the mold wall to remove all the silicone run-off and expose the line between the two halves. I wouldn't recommend actually separating them yet though, as we still need to do the mothermold and we don't want to risk any fiberglass resin managing to flow into there.
Things that went wrong:
- As mentioned in the first thin layer part, I made the mistake of getting distracted with filling problem areas and neglected to actually cover the whole helmet. My first priority should have been complete coverage, then use what I have left to give extra focus to the detail areas. If there's an area that really needs it's own focused work, you can give it it's own micro-layer with a few ml of silicone that's done between the thinned coverage coat and the normal coat if need be.
- While removing the clay, I was a little too aggressive and caused some de-gloving of the 1st silicone half, causing me to need the elastic to ensure the silicone was tight to the master.
- And the big suspenseful mistake I teased earlier during the 1st thin coat: the use of aluminum tape to seal off my keyhole openings. As the name implies, platinum cure silicone is a metal cure, and exposure to certain other metals can cause inhibiting of curing, this is why you can't use platnium-cure and tin-cure silicone together. I'm not sure if aluminum is one of those bad metals, or if my aluminum tape is a tin alloy, but it definitely did cause a problem here. Fortunately though, it's in a part that is going to get cut-out anyway, so it's a lucky mistake to have made it only there.
Besides those though, this went pretty well. The mold turned out with zero bubbles or other issues, and has a pretty consistent thickness throughout and didn't use too much material. You can't ask for too much more than that. Next up will be the mother-mold process, which will probably be a much more simple write-up than this was, since it was messy as hell and I didn't take as many photos.
Feel free to comment or share anything about the silicone process in the meantime.
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Grimstuff
Active Hunter
Thanks Puddles, glad I can contribute something back to the community
Alright, so now we have to do the mother mold. The basic concept behind this is that since the silicone mold is very soft and flexible there’s no way it can hold it’s own shape without some sort of support, so we make a second mold encasing it that is much more rigid.
There’s a lot of different materials that can be used for this, pretty much anything that can be applied into a form and hardens. The two options I see used more often are either fiberglass shells or specialty mother-mold putties such as Smooth-on’s Plasti-paste. The difference between them is pretty much a low price vs ease-of-use thing. Fiberglass costs a little less, but is highly toxic and incredibly messy to work with.. where as Plasti-paste is a little more due to it’s nature as a specialty product, but is a very easy to apply and non-toxic paste.
I’d really like to try working with Plasti-paste in the future, but because I already had some fiberglass sitting around and I wanted to keep things cheap; I elected to go with that method instead. There’s plenty of guides out there for both though, and the raw principles are pretty much the same.
Safety First:
As mentioned, polyester resin (aka, fiberglass resin) is a very nasty toxic chemical. Prolonged contact with it can cause neurological damage and runs the risk of sensitization. This is where contact with the chemical can cause your body to develop an allergic-like response to it, one that can get so bad that even trace contact with the chemical can cause a severe reaction making your hobby very difficult.
Additionally, fiberglass matting, the material that we apply the resin onto which combine to create a rigid shell, is made up of many small fiberglass strands. These can break up into incredibly small fibers that can be very bad if you breathe in or have one land on your eye.
So with all that in mind, I’m going to be doing this outside, wearing nitrile gloves and a high-quality respirator with vapor filters at all times. You should too whenever you’re working with polyester resin or polyester resin products.
Building a mold wall:
Same as for the silicone, this will be another multi-part mold and we need to create a dividing wall between the two halves. Just about any material will work for this if you release it, but aluminum foil seems to have good natural non-stick properties against polyester resin (aka, fiberglass resin).
My personal method for this is to use aluminum tape. I like it because it comes in pretty big rolls so you can fold sections of it in half and create pretty rigid but still bendable walls that can slip right into the existing silicone seam. Additionally since it’s tape, you can just use it to tape segments together, letting it all be one single material.
You pretty much just wanna go around the entire circumference of it like I did here and tuck in into the mold seam. (Excuse the photos being from after I already have one side done as I forgot to take photos earlier on.)
A worry I had here was that since my silicone dividing line sorta went off to the side in the back to avoid the keyholes, I was concerned that the bigger half might be too hard to remove from the mother mold with all the registration keys and such creating mechanical locks. I initially tried to design a 3-part mother mold to accommodate this, but I ended up figuring it was too much hassle and I would see if it works as just a 2 part. Fortunately it did.
Getting the first half on:
After you get your mold wall on, apply a release agent to it. I use Vaseline, which I brush on then wipe to remove excess and get a polish-like covering. I don’t apply it to the actual silicone itself as silicone is anti-sticky enough without oiling it too, and we want the fiberglass to stick to it as much as we can, just focus on the tape.
From there I started cutting up a bunch of the fiberglass matting into roughly 4x4” chunks and then measure out a few 2oz cups of un-mixed resin. I like to mix my resin as several smaller batches so I don’t run the risk of having a bigger batch set-up and begin hardening on me before I can use all of it. The little cups only take a few seconds to mix up when you have them pre-measured. Use either metal or wax paper cups for mixing, as polyester resin will eat through plastic.
My personal application method is to mix up a cup of resin (10 drops per oz of resin), then use a chip brush to pre-apply some onto the project in order to give the matting something to glue to. Then I grab a square of matting, rough it up a little to loosen it, then dab some resin onto it to pre-load it. I then apply the wet matting to the project, pressing it on with a chip brush loaded with more resin. You can get about 2-3 squares done per cup of resin.
You want the matting wet enough so it's completely saturated and sticking flush against the previous layer, but not so wet that it's pooling or dripping.
I tend to get a ring around the mold wall first, then another higher up, then finally cap it off on top. Rinse and repeat. Also, if you need to take a break or finish this over a multiple days, feel free. You don’t need to apply this all at once and letting under-coats dry won’t hurt adhesion.
For a good solid mothermold that won’t crack apart when you separate it, I find about 4 layers around the mold wall and 2-3 layers everywhere else does fine. The mold wall will take the most stress so focus on it, everything else is just there to give the silicone something to hug.
After it’s all on, let it sit overnight to get nice and hard.
Second half:
Flip over your model and remove the silicone tape. Re-apply some Vaseline or preferred release. Feel free to apply it pretty liberally as having these two halves permanently bond would be pretty catastrophic.
Since the tape is now gone, there may be a bit of a gap there now that we kinda don’t want to get filled in. I applied a ring of clay around the whole thing to seal this up.
From there on it’s the same as the first half. Try to use the same amount of layers on the mold wall so one side is not weaker than the other.
Then let it dry overnight again, or at least for a good few hours.
Cracking it open:
Now you’re gonna need to separate these two halves.
First thing I do is get a nice clean edge to the mold by cutting away the stringy edges of the fiberglass on the mold wall. I use a dremel cutting wheel to do this, but you could saw it too.
With all that off, I try to find a spot where the mold line can be seen somewhere along the edge. This can be pretty hard since the fiberglass is so hard pressed against itself, and if you can’t find it at all you might have to guess. I then do a shallow cut on it with the dremel to create a little crevice.
Stick a strong wide flathead screwdriver into it and twist. If all went well it should crack open a little bit. Get a few more screw drivers and start gradually prying it open along it’s length until it pops free.
Now you can finally open everything up and free your original master to enjoy some fresh air again. If you have difficulty separating the silicone halves (you most likely will), pretty much just try to find some visible line between them somewhere, even if you have to pull from the edges, and just slowly and forcefully seperate them from there. If you have a really tough spot, you can use something thin and hard like the back edge of an xacto knife to drag along through the seam and split it.
After all that though, give your mothermold a scrub down with some soap and a brush to remove all the resin and Vaseline residue, and also inspect your silicone mold interior for any imperfections now that it’s finally removed.
Mine had picked up some sanding dust from the deep crevices, and had a weird flashing issue on the visor I had to cut off, but other than that it was a very clean mold.
Prepping the mother mold for casting:
The last thing we need to do is get a way to connect the two mold halves. I just use nuts and bolts.
Find a size you like and matching drill bit (I used 7/16) and go to town. If you want to be fancy, you can fiberglass on the nuts to have them be fixed, that way it’s easier to remove the bolts with a single tool. I haven't done this myself yet though cuz im lazy.
After all that, you’ve got a completed mold and are ready to cast at will. Hurray.
I have already done one test casting so far that I made a few mistakes with, I'll post about it next. Past that though I'm all up to date and we're back to being a WIP.
Mother Mold
Alright, so now we have to do the mother mold. The basic concept behind this is that since the silicone mold is very soft and flexible there’s no way it can hold it’s own shape without some sort of support, so we make a second mold encasing it that is much more rigid.
There’s a lot of different materials that can be used for this, pretty much anything that can be applied into a form and hardens. The two options I see used more often are either fiberglass shells or specialty mother-mold putties such as Smooth-on’s Plasti-paste. The difference between them is pretty much a low price vs ease-of-use thing. Fiberglass costs a little less, but is highly toxic and incredibly messy to work with.. where as Plasti-paste is a little more due to it’s nature as a specialty product, but is a very easy to apply and non-toxic paste.
I’d really like to try working with Plasti-paste in the future, but because I already had some fiberglass sitting around and I wanted to keep things cheap; I elected to go with that method instead. There’s plenty of guides out there for both though, and the raw principles are pretty much the same.
Safety First:
As mentioned, polyester resin (aka, fiberglass resin) is a very nasty toxic chemical. Prolonged contact with it can cause neurological damage and runs the risk of sensitization. This is where contact with the chemical can cause your body to develop an allergic-like response to it, one that can get so bad that even trace contact with the chemical can cause a severe reaction making your hobby very difficult.
Additionally, fiberglass matting, the material that we apply the resin onto which combine to create a rigid shell, is made up of many small fiberglass strands. These can break up into incredibly small fibers that can be very bad if you breathe in or have one land on your eye.
So with all that in mind, I’m going to be doing this outside, wearing nitrile gloves and a high-quality respirator with vapor filters at all times. You should too whenever you’re working with polyester resin or polyester resin products.
Building a mold wall:
Same as for the silicone, this will be another multi-part mold and we need to create a dividing wall between the two halves. Just about any material will work for this if you release it, but aluminum foil seems to have good natural non-stick properties against polyester resin (aka, fiberglass resin).
My personal method for this is to use aluminum tape. I like it because it comes in pretty big rolls so you can fold sections of it in half and create pretty rigid but still bendable walls that can slip right into the existing silicone seam. Additionally since it’s tape, you can just use it to tape segments together, letting it all be one single material.
You pretty much just wanna go around the entire circumference of it like I did here and tuck in into the mold seam. (Excuse the photos being from after I already have one side done as I forgot to take photos earlier on.)
A worry I had here was that since my silicone dividing line sorta went off to the side in the back to avoid the keyholes, I was concerned that the bigger half might be too hard to remove from the mother mold with all the registration keys and such creating mechanical locks. I initially tried to design a 3-part mother mold to accommodate this, but I ended up figuring it was too much hassle and I would see if it works as just a 2 part. Fortunately it did.
Getting the first half on:
After you get your mold wall on, apply a release agent to it. I use Vaseline, which I brush on then wipe to remove excess and get a polish-like covering. I don’t apply it to the actual silicone itself as silicone is anti-sticky enough without oiling it too, and we want the fiberglass to stick to it as much as we can, just focus on the tape.
From there I started cutting up a bunch of the fiberglass matting into roughly 4x4” chunks and then measure out a few 2oz cups of un-mixed resin. I like to mix my resin as several smaller batches so I don’t run the risk of having a bigger batch set-up and begin hardening on me before I can use all of it. The little cups only take a few seconds to mix up when you have them pre-measured. Use either metal or wax paper cups for mixing, as polyester resin will eat through plastic.
My personal application method is to mix up a cup of resin (10 drops per oz of resin), then use a chip brush to pre-apply some onto the project in order to give the matting something to glue to. Then I grab a square of matting, rough it up a little to loosen it, then dab some resin onto it to pre-load it. I then apply the wet matting to the project, pressing it on with a chip brush loaded with more resin. You can get about 2-3 squares done per cup of resin.
You want the matting wet enough so it's completely saturated and sticking flush against the previous layer, but not so wet that it's pooling or dripping.
I tend to get a ring around the mold wall first, then another higher up, then finally cap it off on top. Rinse and repeat. Also, if you need to take a break or finish this over a multiple days, feel free. You don’t need to apply this all at once and letting under-coats dry won’t hurt adhesion.
For a good solid mothermold that won’t crack apart when you separate it, I find about 4 layers around the mold wall and 2-3 layers everywhere else does fine. The mold wall will take the most stress so focus on it, everything else is just there to give the silicone something to hug.
After it’s all on, let it sit overnight to get nice and hard.
Second half:
Flip over your model and remove the silicone tape. Re-apply some Vaseline or preferred release. Feel free to apply it pretty liberally as having these two halves permanently bond would be pretty catastrophic.
Since the tape is now gone, there may be a bit of a gap there now that we kinda don’t want to get filled in. I applied a ring of clay around the whole thing to seal this up.
From there on it’s the same as the first half. Try to use the same amount of layers on the mold wall so one side is not weaker than the other.
Then let it dry overnight again, or at least for a good few hours.
Cracking it open:
Now you’re gonna need to separate these two halves.
First thing I do is get a nice clean edge to the mold by cutting away the stringy edges of the fiberglass on the mold wall. I use a dremel cutting wheel to do this, but you could saw it too.
With all that off, I try to find a spot where the mold line can be seen somewhere along the edge. This can be pretty hard since the fiberglass is so hard pressed against itself, and if you can’t find it at all you might have to guess. I then do a shallow cut on it with the dremel to create a little crevice.
Stick a strong wide flathead screwdriver into it and twist. If all went well it should crack open a little bit. Get a few more screw drivers and start gradually prying it open along it’s length until it pops free.
Now you can finally open everything up and free your original master to enjoy some fresh air again. If you have difficulty separating the silicone halves (you most likely will), pretty much just try to find some visible line between them somewhere, even if you have to pull from the edges, and just slowly and forcefully seperate them from there. If you have a really tough spot, you can use something thin and hard like the back edge of an xacto knife to drag along through the seam and split it.
After all that though, give your mothermold a scrub down with some soap and a brush to remove all the resin and Vaseline residue, and also inspect your silicone mold interior for any imperfections now that it’s finally removed.
Mine had picked up some sanding dust from the deep crevices, and had a weird flashing issue on the visor I had to cut off, but other than that it was a very clean mold.
Prepping the mother mold for casting:
The last thing we need to do is get a way to connect the two mold halves. I just use nuts and bolts.
Find a size you like and matching drill bit (I used 7/16) and go to town. If you want to be fancy, you can fiberglass on the nuts to have them be fixed, that way it’s easier to remove the bolts with a single tool. I haven't done this myself yet though cuz im lazy.
After all that, you’ve got a completed mold and are ready to cast at will. Hurray.
I have already done one test casting so far that I made a few mistakes with, I'll post about it next. Past that though I'm all up to date and we're back to being a WIP.
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Grimstuff
Active Hunter
There's a lot of great slush casting guides out there from guys a lot more experienced at it than me, so I won't bother with any elaborate write-ups here (it's really something that needs a video anyway). I can share the mistake I made with my inaugural pull though to keep others from repeating it.
The last urethane castings I've done were just for some small items and quite a while ago, so I had kinda lost respect for how sensitive it is to introduced air. I neglected to use some anti-bubble techniques I should have, especially on the first layer which is the most critical. I pretty much just straight mixed the urethane after shaking it and poured it in.
I quickly wised up after I saw how bubbly the first layer was and started degassing my layers afterwards, but the damage was pretty much already done. After I released it from the mold it's really apparent just how bad the bubbling was.
It's pretty bad, but it's not a total loss. It'll be some work, but I can sand it down and smooth it up with bodyfiller. I'll keep it as my own personal banger helmet that I can do test-paints on and such.
So urethane casting protips:
The last urethane castings I've done were just for some small items and quite a while ago, so I had kinda lost respect for how sensitive it is to introduced air. I neglected to use some anti-bubble techniques I should have, especially on the first layer which is the most critical. I pretty much just straight mixed the urethane after shaking it and poured it in.
I quickly wised up after I saw how bubbly the first layer was and started degassing my layers afterwards, but the damage was pretty much already done. After I released it from the mold it's really apparent just how bad the bubbling was.
It's pretty bad, but it's not a total loss. It'll be some work, but I can sand it down and smooth it up with bodyfiller. I'll keep it as my own personal banger helmet that I can do test-paints on and such.
So urethane casting protips:
- Degass it just like you do your silicone, for at least a solid 2 minutes to make sure it's absolutely flattened. If you have a quick-set silicone with a very short pot life, you can degass it un-mixed, just be carefully when stirring it later. If you don't have a vacuum chamber, then at least let it sit and calm for a bit after shaking it.
- Also when pouring and slushing it, be careful to not be too aggressive and introduce air via splashing.
- Spray release your mold some before casting, it helps preserve the mold and makes the initial urethane slush go on smoother.
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Grimstuff
Active Hunter
Got a second casting done yesterday, this one came out super clean is pretty much free of any issues whatsoever . I'm pretty proud of it.
I'm starting to get the rotocast method down a lot better too, the last helm looked a bit lumpy inside.
For the first two layers I go a little bit liberal with the amount and let the excess pool in the ears, and from there it's just consistent identical coatings. I'm still not completely settled on how many layers to end on though, the first helm ended on about 5 and is a little more flimsy than I like. This newest one is 7, and although I haven't cut out the visor yet which the most delicate section, it does seem more solid.
Anywho, some shots of the two together, dunce helmet on the left and new on the right. You can really see the quality difference in the rear shot.
. I'm pretty proud of it.I'm starting to get the rotocast method down a lot better too, the last helm looked a bit lumpy inside.
For the first two layers I go a little bit liberal with the amount and let the excess pool in the ears, and from there it's just consistent identical coatings. I'm still not completely settled on how many layers to end on though, the first helm ended on about 5 and is a little more flimsy than I like. This newest one is 7, and although I haven't cut out the visor yet which the most delicate section, it does seem more solid.
Anywho, some shots of the two together, dunce helmet on the left and new on the right. You can really see the quality difference in the rear shot.
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Grimstuff
Active Hunter
Silicone for the rangefinder pieces finally came in. I went with Mold-Star 20T which is a semi-transparent silicone part of the Mold-Star line. No particular reason I went with this stuff, it was just the only Smooth-on platinum silicone being sold on Ebay when I looked (ebay is way cheaper on shipping for single items than ordering direct from a Smooth-on distributor).
I just did some simple block molds for all the parts, 1-part molds for the really simple stuff like the stalk and perspex block and 2-part for the ear cap and rangefinder housing. The rangefinder housing was the most tricky, as it has that big hollow cavity that the perspex block fits into which usually is a big no-no when it comes to mold making. At first I was considering just molding the housing and perplex block together as one solid piece, but that would pretty much kill any options for being able to do LED wiring. So instead I just yolo'd it and made a really careful 2-part mold that seems like it'll work out fine.
As for the actual mold-making method, there's plenty of good guides out there on block molding so I won't waste words trying to imitate them; Punished Props has a particularly good series on basic moldmaking. The only thing I do that's somewhat-uncommon-but-not-really is to use Legos for my mold wall; both because it's easy to make molds of any size/shape outta them, and cuz it's fun.
Turns out the transparency is kinda neat, you can tell how cured it is by how cloudy it becomes, and it's good for seeing if there's any bubbles in your mixture too. I might just keep using it in the future.
I just did some simple block molds for all the parts, 1-part molds for the really simple stuff like the stalk and perspex block and 2-part for the ear cap and rangefinder housing. The rangefinder housing was the most tricky, as it has that big hollow cavity that the perspex block fits into which usually is a big no-no when it comes to mold making. At first I was considering just molding the housing and perplex block together as one solid piece, but that would pretty much kill any options for being able to do LED wiring. So instead I just yolo'd it and made a really careful 2-part mold that seems like it'll work out fine.
As for the actual mold-making method, there's plenty of good guides out there on block molding so I won't waste words trying to imitate them; Punished Props has a particularly good series on basic moldmaking. The only thing I do that's somewhat-uncommon-but-not-really is to use Legos for my mold wall; both because it's easy to make molds of any size/shape outta them, and cuz it's fun.
Turns out the transparency is kinda neat, you can tell how cured it is by how cloudy it becomes, and it's good for seeing if there's any bubbles in your mixture too. I might just keep using it in the future.
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Grimstuff's Scratch Build Journal
Very nice work, I recently completed a helmet for my 7 year old using the same templet, I have an adult sized one about 25% done as well but may rebuild it with some of the tips here.
For the dunce helmet the first thing I thought was that would make an awesome sarlacc pit acid etched helmet, using iron powder paint in all the pits, just sayin!
Sent from my iPhone
Very nice work, I recently completed a helmet for my 7 year old using the same templet, I have an adult sized one about 25% done as well but may rebuild it with some of the tips here.
For the dunce helmet the first thing I thought was that would make an awesome sarlacc pit acid etched helmet, using iron powder paint in all the pits, just sayin!
Sent from my iPhone
Grimstuff
Active Hunter
That's actually a really good idea. Might be able to even acetone melt it a little to add to the effect. Unfortunately... I already did some filling work on that bucket and mostly have the bubble pits all gone now, but I kinda want to purposefully mis-cast another just to explore that idea. I'll have to keep it in my pocket.
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Grimstuff
Active Hunter
Yep sure do. I gave it a really quick mention earlier during the big silicone post, but I guess it'll be good to go into it a little bit more detail since it's such a useful tool.
You can of course buy them from companies like Smooth-on and BestValueVacs, but I actually made my own since those are usually quite expensive.
It's essentially just a large aluminum stock-pot, with a thick polycarbonate/Lexan lid (at least 3/8th inch think and 10x10" or greater), and some piping. Very cheap and easy to make, especially if you already have the pipe fittings and stuff l like I did. If not, then it's pretty much using 2x ball valves, 1x 3-way T, 1x nipple, 2x hose barbs, and 1x length of cut plastic hose from Home Depot. You'll also need a drill and tap to make threads into the acrylic to screw it into. Dunno how much all that comes to, but you can get the most of it from Harbor Freight for cheap. The gauge is optional, and I kinda jury rigged it onto the top of the T by drill and tapping it's top. You could just do one in-line somewhere before the ball-valves though if you want one.
For the rubberized seal part I just masked off a circle shape on the acrylic and spray painted several layers of Plasti-dip onto it. It holds vacuum incredibly well, I've left it locked overnight before with zero visible drain on the gauge.
More expensive than the chamber itself will be the vacuum pump. Harbor Freight sells two models, a weaker one for $100 and a somewhat better one for $150. If you're an experienced Harbor Freight shopper though you can get em for cheaper with good sale and coupon usage. I got the better one for around ~$110. (it's output is threaded for car A/C systems though, so another $10 or so for some NPT fittings to replace them)
So all in all, chamber + pump, you're looking at around a ~$150 dollar item, much cheaper than buying a pre-made one which is ~$150 for only the chamber. It's definitely still a pricey investment though, and you can get by without one with a lot of careful anti-bubble practices, but if you do this sorta work pretty often it's pretty worth it.
As for safety, vacuum chambers are a lot safer than things like pressure chambers, implosion rather than explosive forces and all. The biggest risk I can think of is if you do something dumb like use thin glass for the lid or something. Just to CMA though, don't take this post as me telling you to make one or anything, I'm just showing you guys what I made. Repeat at your own risk and such. But yeah, it's a really useful tool.
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