First Silicone Mould

[BoomerangInfo]

OK Folks,

Boy, working with this stuff is like working with melted marshmallows, only thicker. Vacuum sure would help get the bubbles out of this stuff. Despite my fears from what was rising to the top of the mixture once it was poured in the master, the end result seems to be pretty much bubble free except for underneath, where it doesn't matter. I did a lot of bashing the workbench with a hammer to try and de-gas, which must have helped.

I had to destroy my master to get it out, but apart from that, I'm quite happy with the result. Now to go throw some resin in and see how it comes out.

I have enough silicone left to make two more if I can remake my master. Needs a remodel to get the end result out easier.

What do you think?

Russell.

[Big Shed]

Interesting project Russell, what is the significance of the different colour silicones? The moulds (molds?) I purchased from Gadget on IAP are a light purple, yours is light blue.

Be interesting to see how your blanks come out, what size will they be?

Only observation I have is that the left side of your mould, particularly the bottom left, seems a bit thin.

Oh, forgot to ask, what will your 3 moulds have cost you by the time you finish them?

[BoomerangInfo]

Interesting project Russell, what is the significance of the different colour silicones? The moulds (molds?) I purchased from Gadget on IAP are a light purple, yours is light blue.

Be interesting to see how your blanks come out, what size will they be?

Only observation I have is that the left side of your mould, particularly the bottom left, seems a bit thin.

Oh, forgot to ask, what will your 3 moulds have cost you by the time you finish them?

The different colours seem basically for slightly different compositions of silicone and/or different companies. The silicone itself is white, and they colour the catalysts as a visible indicator of how well your mixing is. if there's any white bits left, you haven't mixed enough.

Different coloured catalysts will indicate different final results with variations in

1. Viscosity
2. Gel time
3. Set time
4. Strength (this and set time seem to be the main considerations by the manufacturers)
5. Working temperature etc etc

Blanks will be 130x20x20 once they are out, with maybe 1mm varation from what I've measured. The wall thicknesses are basically even, must be an optical illusion if it looks thinner. The calipers tell me there is at most .8mm difference across all the walls, which are approximately 8mm thick. Base should be 1 - 1.2mm, depending on how close I got to my measurement line before I ran out of silicone.

Sizes could be increased a little, but I calculated all the sizes originally to get me 3 moulds out of 1Kg of material, and those were the optimal sizes. My only hiccup was a little underflow in my master where I hadn't seated the pieces in the middle down flat, so I had to do a little trimming, hence the slightly raggedy edges. it's only on the top though, so won't affect the blanks.

For the Silicone alone in that size, it's $64-$68, depending on whether I get it delivered to Brisbane or Warwick. Add on a couple $$ for consumables so around $70 - $75 for the three, not counting material costs for the master, which my prototype was basic pine & ply anyway. Making the master took me an elapsed day, with trying to get exact measurements, figuring out the best material to seat it all, gluing, finishing and drying. But as I said will need a redesign & material rethink to enable easy removal of the mould, without leaking, and without destroying the master each time.

If it all goes well, I plan to try and make a few more in various sizes for specific kits, worthless wood casting, and casting with tubes in for label casting etc.

To help fund all this experimentation, if anyone is interested, I'm willing to sell a few moulds. For the one above, I'd be looking at charging $30. If no one's interested, that's OK too, my experiments will just take longer is all.

I'll post the blanks I've just put in (well one of them anyway, the others are a secret :;) when they come out tomorrow.

Russell.

[bsrlee]

Judging from the colour of the finished mold, the RTV you are using is made by Whacker in Germany - they like blue dye in their catalysts. Depending on the exact mix number (there is considerable 'rebadging' of product by resellers to keep users in the dark), it is very long lasting when used in contact with Polyurethanes, something that can NOT be said for many other RTV's, and is a great favourite with movie SPFX technicians for molds.

If your mold goes brittle after a hundred or so castings, you need to ask around for the Whacker RTV that is formulated for casting Polyurethane.

[BoomerangInfo]

Judging from the colour of the finished mold, the RTV you are using is made by Whacker in Germany - they like blue dye in their catalysts. Depending on the exact mix number (there is considerable 'rebadging' of product by resellers to keep users in the dark), it is very long lasting when used in contact with Polyurethanes, something that can NOT be said for many other RTV's, and is a great favourite with movie SPFX technicians for molds.

If your mold goes brittle after a hundred or so castings, you need to ask around for the Whacker RTV that is formulated for casting Polyurethane.

It's locally marketed as Maximould, and yes, it is especially for PU & PE resin casting, to resist the degrading effects, which is why I went for it instead of some of the others. They still advise to use some sort of release, or apparently the surface in contact with the resins eventually goes leathery.

Russell.

[dai sensei]

Looks like a pro job to me :2tsup:

If you are selling, count me in for one Russell please. I'm on holiday at the moment though, using someone else's computer, but hopefully we can work something out when I get back in 4 weeks. I'm looking to use mould for stabilising timber blanks rather than casting pure resin blanks.

Cheers

[dj_pnevans]

Russell all looks go to me, I am looking at doing this soon. All I was going to do was use 3 to 4 blanks glue or nail to a board and put a border around that and use as the master. Where did you get yours from.
David

[BoomerangInfo]

Russell all looks go to me, I am looking at doing this soon. All I was going to do was use 3 to 4 blanks glue or nail to a board and put a border around that and use as the master. Where did you get yours from.
David

There are a couple of sources available, but in the end, Barnes was easiest to get it from.

Russell.

[BoomerangInfo]

Looks like a pro job to me :2tsup:

If you are selling, count me in for one Russell please. I'm on holiday at the moment though, using someone else's computer, but hopefully we can work something out when I get back in 4 weeks. I'm looking to use mould for stabilising timber blanks rather than casting pure resin blanks.

No worries Neil,

Give me a yell when you're back and we can discuss your requirements. Enjoy the holiday!

Russell.

[Simomatra]

Great looking job Russell. They don't look dis-similar to those I got from Gadget

I will be casting today.

[BoomerangInfo]

Well, here's the first one out of the mould. Sooooo much easier than the cutting board moulds, and it's clean ready to go again - more more scraping spilled resin off of the outside or rewaxing the leaky edges before the next cast. I reckon this easily triples the rate I can cast blanks.

Russell.

[gawdelpus]

Hehe! I think I have a kit looking for one of those ! :) its all a learning experience ,then just refining and improving techniques ,once the basics are in place the rest just follows ,so much to learn !so many things to try , but having fun is the main ingredient hehe, Cheers :U

[NewLondon88]

Looks fine to me!

You can help the bubbles clear if you put the poured mold on something that vibrates.
I use a scroll saw for mine. I put it on top of the arm which vibrates/oscillates like crazy.
Warming before you pour can help, too.

If you've got any Corian you can make masters out of that. They polish great (helps with
release) and you can wax them (also helps with release)

10% petroleum jelly warmed and mixed with mineral spirits will help with release, but
for silicone, you'd really want the release they recommend. (something like Stoner)

When making your mold box, just make sure it isn't bigger than your pressure pot.
DAMHIKT :-

Nice job

[BoomerangInfo]

When making your mold box, just make sure it isn't bigger than your pressure pot.
DAMHIKT :-
Nice job

Hehe, that's why i went for 3 wide only, not 4. No corian here I'm afraid. I was going to order some Stoners when I ordered the silicone, but at $24 for the can, I thought I'd see how I went first in case it was all a big flop.

Hey, do you know, once you have a set silicone mould, can you cast silicone into it, or does silicone stick to silicone, if you get my drift?

Russell.

[Sawdust Maker]

In one of the IAP articles/tutorials there was a suggestion that you could add silicone to a mould later (he was using plumbers silicone). Seemed to suggest that it would bond well.

I did wonder whether the plumbers sticks of silicone would be cheaper then the silicone you used in your mould.

Corian is used in Aus for kitchen benches. I've got to get off my behind and see if I can get some offcuts from the local kitchen purveyors.

[BoomerangInfo]

I did wonder whether the plumbers sticks of silicone would be cheaper then the silicone you used in your mould.

It would be cheaper, but the problems you'd have trying to get it to flow neatly into your master would be an extreme hair pulling exercise I reckon. Plus I don't know how resistant it is to wear & tear both physical & chemical.

Russell.

[NewLondon88]

Hey, do you know, once you have a set silicone mould, can you cast silicone into it, or does silicone stick to silicone, if you get my drift?
Russell.

Silicone doesn't stick to much of anything EXCEPT silicone!

You need a special type of release to get it not to stick. I'm not sure where to get it,
but I know I've seen suppliers mention it.

[bsrlee]

Silicone RTV does stick to itself, in fact it is the only thing it will bond to, and it will not let go. This is useful in that you can chop old scrap RTV up finely & use it as 'filler' in non critical parts of a new mold.

However you can use a number of things to get RTV to release/not stick to itself - the easiest is to just rub some Vaseline/petroleum jelly over the area not to be bonded. Make sure you get some down the outside of the mold too, not just the part line as RTV can creep into tiny spaces & glue things together.

You will find that when making a 2 part mold it is quite hard to get the parts to separate as there is a very exact mechanical fit which makes it seem like it has set solid - did you remember the parting agent? - then suddenly it lets go. One shop I know just casts the mold in one piece with steel locating pins thru both halves, then cuts one side of the mold thru' to the master inside. When you can release the master you have cut far enough - but the master has to be either very hard or expendable for this to be viable.