Advice on creating a helmet mould

[mazdachris]

Afternoon,

Sorry if this gets asked a lot. It probably does.

I've been making a Sabine Wren style mandalorian helmet for the past few months, built from a basic pep file and then resin'ed, fillered, sanded, painted, etc. The intention was always to make a mould of the original and then cast from it. I had a crack at doing so - a single-piece silicone mould with a two-part fibreglass shell. This was my first attempt as casting anything larger than a badge

On my first attempt at casting, it looks like as I was slushing the resin in the mould, bits of the mould were falling away from the shell, and the end result was very crumpled.

I think my problems were threefold:

• The silicone I used for the mould was not thick enough and so didn't hold its shape correctly. Making a new silicone jacket should help it hold its shape.
• I used six registration keys, about two inches across - one on each side of the dome and the other four arranced equally around the sides. This doesn't seem to have been adequate.
• I don't think I used enough resin and probably added tot he damage because it wasn't strong enough when I demoulded.

The solution to the latter is easy. I used three cups of resin, probably I would have been better off with five.

I can make a new mould, I have lots of silicone. It a pain, but fine. I can make it thicker - what kind of thickness would be best? Around 10mm or so? Thicker? I left it as one piece with no relief cuts but I could put a relief cut up the visor to allow it to demould easier with less manhandling.

The thing I'm struggling to get my head around is the best number, size, and placement, of the registration keys to make sure that it remains firmly in place under the shell, while still being possible to physically remove the shell. While I've seen lots of videos and guides detailing how to make registration keys, and stressing that you should use registration keys, it's mostly left to trial and error to determine the best size shape and placement. FWIW I think mine were probably too few, and too big.

Has anyone got any thoughts or advice on this latter point? There doesn't seem to be much consistency of approach so I guess people all have their own techniques.

Thanks for any help people can give!

 

[ChickenHaunt]

Pictures of your mold and casting will help

 

[mazdachris]

Good point!

So here's the original from which I took the mould:




Here's the mould:



And here's the floppy nonsense that came out of it:

 

[Alric]

The mould does seem a bit thin as you can still see the colour of the master.

 

[Darth Lars]

Also, with large moulds such as this it is common to use a "mothermould" of fibreglass (or other hard material) around it to prevent warping.
If the mould has undercuts then the mothermould will need to be in two (or more) parts that are fastened together when casting and can be taken apart when demoulding.

 

[mazdachris]

Sorry, yes, not pictured here is a two-part mother mould made from fibreglass, hence the registration keys. That's what I'm calling them anyway, those little circular nubbins dotted across the surface. I think the issue really is that the bits between the keys holding it decure to the mother-mould were too thin, so simply the weight of the resin slushing was enough to stretch and dislodge them.

So, if the issue is basically that it's too thin, and that the registration keys are fine, then do I start again from scratch, or put the silicone mould back onto the master and add more layers? That would be easier than starting again, for sure, but feels like there's great potential there for it not going back on quite right and ending up knacked.

The plus side is that the silicone has picked out the detail perfectly, so if I am able to rescure this silicone mould then I'm optimistic that I'll get really nice casts from it with virtually no finishing needed.

 

[Kevin Gossett]

Is the mother mold made of fiberglass or silicone? In your first post you mentioned silicone.

 

[mazdachris]

Fibreglass. Definitely fibreglass.

I guess I need to add proofreading to my list of things I need to improve. Alongside mouldmaking and personal hygiene..

 

[zorg]

mold wall thickness looks way too thin.

instead of wasting several gallons on those unnecessary registration plugs you should have used the material to build up the wall of the mold.

just say no to reg plugs, the cake is a lie.

 

[mazdachris]

How thick should it be, ideally?

 

[zorg]

how many casts are you likely gonna need out of it?

the thicker it is the longer it will last

the thicker it is the less chance of unevenness in your casts.

i usually try to get about 10mm even wall thickness but i want my molds to last.

i think i would not go less than 5mm if i wanted a mold i could take a few casts from.

you can see one of my silicone molds in this thread if its any use to you, i know its not exactly the thing you're doing but close enough.

its reg plug free

http://www.therpf.com/showthread.php?t=258801

 

[OldKen]

To Zorg you must listen, mind what you have learned!

Seriously, I don't think Z is capable of making a bad casting. If he ever has, I've not heard about it!

Your original finished pep looks really good! Hopefully the next mold isn't a "waste"! (See what I did there?)

Good luck! Can't wait to see a finished and painted casting.

 

[mazdachris]

Not sure how many casts I want to pull from it. I have a few people who have asked about them, and I'd happily cast more if people show an interest.

That's a great tutorial, just the sort of thing I needed. So many people do video guides and they spend so long going on and on showing the mixing processes of resins and stuff but never seen to detail the structural 'engineering' of a decent mould.

It's the first time I've ever tried this so I never expected it to be perfect first go. It's a learning process for sure.

Thanks for the advice, I'll put up pictures of my progress.

 

[zorg]

you could build a decent mold that will last years, once it's done it's done. You can sit back and let it earn you $$ whenever you need.
I really really hate making molds so I tend to do ones that last just so I don't have to do it again.
The way I did the mold is by no way the only way, it's just the way I do it. It works for me.
I have done the process of putting a layer of clay over the master sculpt then do the mother mold then remove the clay and replace it with silicone. It's just what you can be bothered with really.

Hope you can take something from the tutorial and good luck with the next one.

Thanks for the positive feedback oldken, appreciate it. They broke the "mold" when they made you.......I'll get my coat.

 

[mazdachris]

Well after some more work on the mould I managed to get the pull on the left. Not perfect, far from it, but useable. Unfortunately having gone far thicker on the mould, I ended up tearing it while demoulding. Le sigh. So no quick quids for me..

Thanks again for the advice chaps.

 

[OldKen]

Much better!

Sorry about the mould.

I bet you will nail the next time you try to do a similar mould though!

 

[mazdachris]

I hope so. One important thing I have learned: condensation cure and addition cure silicone don't stick together.