Silicon casting moulds

[BoomerangInfo]

Hey Folks,

Well I'm finally taking the plunge and going to make some silicon moulds for casting pen blanks. The silicon will hopefully arrive next week, and in the meantime I have to make up my master.

I'm going to start with a 3 blank flat mould, for blanks 20x20x130mm, as that requires about 180mls of resin to fill the mould, which is a good quantity for mixing in the 210ml disposaable plastic cups I'm using to mix my resins.

I have to option of making my master with 3 different types of bottom for each blank.

1. Flat, square
2. Round (semi-circle bottom, top would still be square)
3. Rounded corners square (i.e. bottom long edge of blank would not meet at a 90 degree corner, but would have a 2mm or so profiled corner like a roundover bit on a router produces)

While #2 would save resin, I'm thinking it's too impractical to deal with the end shape. If things work out with this, I'd contemplate making a vertical blank mould later to do straight round rods.

What I was wondering, do people think there would be a problem with rounding off the square corners on the bottom of the blank? This would make is slightly easier to demould, and save a (very small) amount of resin, but what you are losing is a 90 degree corner on your blank.

Personally I've never needed a 90 degree corner, so see no problem with doing this, but does anyone have any reasons why their blanks need 90 degree corners?

Thanks. Russell.

[crow400]

Don't see any problem in not having a 90 degree corner Russell. Some of the blanks I've resawn from irregular timber were fairly strange shapes. Just need care in centering the drill hole.
Crow

[Simomatra]

Russell
I use electrical conduit as well, 25mmm gives you 19mm internal diameter. No de-bonding necessary just tap and it falls out or a bit of compressed air down the side. square corners nd round bar make for easier center drilling

[BoomerangInfo]

Russell
I use electrical conduit as well, 25mmm gives you 19mm internal diameter. No de-bonding necessary just tap and it falls out or a bit of compressed air down the side. square corners nd round bar make for easier center drilling

Yeah the problem with vertical moulds that I can see is the ability to properly control swirling, although they'd be good for a layered effect, which I haven't tried yet. I also have a vertical made up for label casting, with an integrated plug that holds the tube centred. I just haven't got around to trying it out yet to see whether the theory works in practice.

Russell.

[Skew ChiDAMN!!]

If ease of swirling is a factor, then what's wrong with simply making a wooden tray and lining it with glad-wrap or similar? Then cutting up the slab into blanks?

Just being curious... :wink:

[BoomerangInfo]

If ease of swirling is a factor, then what's wrong with simply making a wooden tray and lining it with glad-wrap or similar? Then cutting up the slab into blanks?

Just being curious... :wink:

Absolutely nothing, until you try it :) PE Resin is not the simplest stuff to work with. It knows exactly where the worst place it could end up is, and heads there as quickly as it can. I suspect keeping the glad wrap etc in a nice flat manner so the blanks didn't have crinkled glad wrap embedded could be a problem. Of course there are other options besides glad wrap - wax, alfoil, heck, even vaseline might work, but they're all messy and require repeating the procedure every time you make a bank.

My current 4-blank mould is a larger cutting board mould which works exactly like this and it does the job well in the end, but leaks, ease of removal, finish on the blank etc just makes it annoying if you're doing it regularly and for sale, compared to what you can get out of a silicon mould.

Having a silicon mould with multiple individual blank sections (which admittedly is harder to swirl than 1 big block) also allows better customisation of the blank length, more efficient pressure pot usage than multiple individual moulds if you want to do several different ones at once, and I have some ideas to try and make pre-embedding the tube simple as well with some custom moulding, which wouldn't be as easy with another material.

We could all be making our pens by sanding a piece of wood chucked in a drill too, but I don't think anyone would chose that as their preferred method after more than 1 or 2 pens. I'm just trying to streamline my workflow, and produce a more "professional" looking result, but it is at the cost of investing in the materials to do it in the first place, which aint cheap.

Russell.

[schaf]

Russell,for molds I use melamine MDF,super glue it together and hot wax the joins.
no leaks. Only use the mold once and throw it away.

Terry

[Skew ChiDAMN!!]

Fairy nuff... especially given:


I'm just trying to streamline my workflow, and produce a more "professional" looking result, but it is at the cost of investing in the materials to do it in the first place, which aint cheap.

"I do a lot of them" would've satisfied me, too. :D

[BoomerangInfo]

Russell,for molds I use melamine MDF,super glue it together and hot wax the joins.
no leaks. Only use the mold once and throw it away.

Terry

You throw it away after one go? Why? It should be good for more than one shouldn't it?

Russell.

[BoomerangInfo]

"I do a lot of them" would've satisfied me, too. :D

LOL, was just trying to give you my reasoning. You can come back and ask again after I've used up my $100 of silicon and end up with a blank that looks like the hunchback of Notre Dame. I may have a different answer then :p

Russell.

[Skew ChiDAMN!!]

I've made a few, purely on a hobbyist basis for myself, so I understand your reasoning.

I like wooden moulds so I can simply unscrew the sides to remove the slab, but you're spot on about wrinkles in the bloody liner. Still, because the blanks were only for me, that's not really a major concern :)

[schaf]

Melamine is cheap, I cut it into 30mm strips for the sides and glue it up.If you wish to use it more than once then you would have to clean it.

[joe greiner]

Hey Folks,

Well I'm finally taking the plunge and going to make some silicon moulds for casting pen blanks. The silicon will hopefully arrive next week, and in the meantime I have to make up my master.

I'm going to start with a 3 blank flat mould, for blanks 20x20x130mm, as that requires about 180mls of resin to fill the mould, which is a good quantity for mixing in the 210ml disposaable plastic cups I'm using to mix my resins.

I have to option of making my master with 3 different types of bottom for each blank.

1. Flat, square
2. Round (semi-circle bottom, top would still be square)
3. Rounded corners square (i.e. bottom long edge of blank would not meet at a 90 degree corner, but would have a 2mm or so profiled corner like a roundover bit on a router produces)

While #2 would save resin, I'm thinking it's too impractical to deal with the end shape. If things work out with this, I'd contemplate making a vertical blank mould later to do straight round rods.

What I was wondering, do people think there would be a problem with rounding off the square corners on the bottom of the blank? This would make is slightly easier to demould, and save a (very small) amount of resin, but what you are losing is a 90 degree corner on your blank.

Personally I've never needed a 90 degree corner, so see no problem with doing this, but does anyone have any reasons why their blanks need 90 degree corners?

Thanks. Russell.

Silicon? or silicone? I've fabricated some stuff in silicone (ordinary sealant/caulking) by sort of a lost wax process. I carved a core in paraffin wax, then coated it with sealant, smoothing with lighter fluid (naphtha), which was listed for cleanup. After a few days, I heated it gently to drain the wax through a lower integral pipe nipple. It was a DIY huffenpuffer for a cheapo scroll saw that didn't have a pump. The nipple held a piece of vinyl tubing wrapped with "rigid" electrical wire for adjustment toward the spraying end. I learned about the tennis ball trick afterwards.

Open top (squarish) will provide best access for custom swirling. With flexible moulds, all four corners of a square wax master could be rounded for uniformity without seriously compromising access. Square top and round bottom is probably the worst shape for later work, IMHO.

Food for thought. Dessert later, if you like.

Cheers,
Joe

[NewLondon88]

Rounding off the corners shouldn't be a problem (I hope not, that's what I'm doing :oo: )
and you'd be turning off those corners anyway. And it does save resin.

For swirling, why not eliminate the individual blanks and just go with a slab?
Gives you more room to get figuring in the PR, and then just cut into blanks
afterwards?

[BoomerangInfo]

Rounding off the corners shouldn't be a problem (I hope not, that's what I'm doing :oo: )
and you'd be turning off those corners anyway. And it does save resin.

For swirling, why not eliminate the individual blanks and just go with a slab?
Gives you more room to get figuring in the PR, and then just cut into blanks
afterwards?

That's down the track. At the moment I have an immediate need to cast a dozen Banksia pods at once, and doing them in a slab creates some logistic problems. I have other embedding plans too, which work better individually. Also, my slab cutting board mould is working much better than my individual cutting board moulds currently, so things are happening in priority order.

So yours are rounding the corners. Only on the bottom, or are you trying the top too as Joe suggested? I was worried about doing the tops and making it harder to remove the set blanks, which would also cause additional mould wear reducing it's working life.

Russell.

[NewLondon88]

So yours are rounding the corners. Only on the bottom, or are you trying the top too as Joe suggested? I was worried about doing the tops and making it harder to remove the set blanks, which would also cause additional mould wear reducing it's working life.
Russell.

I left the top alone, for the reasons you've mentioned. It's hard enough to get your
fingers in there as it is, let alone with a rounded top. Besides, that would involve
making a two part mold. I'm a noob, here. :p

[Simomatra]

You can also get a silicone cooking tray pour your PR do the swirling and then cut into blanks. That way you can also make thin sliver on glass and ad them like a birds nest

Do a web search there re many ways out there and lots of tutorials on U tube

Conduit an also be used on the horizontal centre hole to fill and a track cut the length of the conduit use conduit caps on each end

[tea lady]

Silicon? or silicone? I've fabricated some stuff in silicone (ordinary sealant/caulking) by sort of a lost wax process. I carved a core in paraffin wax, then coated it with sealant, smoothing with lighter fluid (naphtha), which was listed for cleanup. After a few days, I heated it gently to drain the wax through a lower integral pipe nipple. It was a DIY huffenpuffer for a cheapo scroll saw that didn't have a pump. The nipple held a piece of vinyl tubing wrapped with "rigid" electrical wire for adjustment toward the spraying end. I learned about the tennis ball trick afterwards. What about using a "baby enema" Available from chemists. Just try not to think what they are really used for.

Cheers,
Joe

Other thought on silicon molds. how about using stickytape. I do that over my forms when I an laminating veneer. No sticking. Stays put where you want it.

Another thought is those Ice block silicon trays you can get from cooking shops, like the General Trader. Ive even sseen them in the $2 shops. :shrug: The long skinny ones are for ice blocks to put in drink bottles.:cool:

[NewLondon88]

The long skinny ones are for ice blocks to put in drink bottles.:cool:

I had the hardest time finding those .. in fact, another turner found them for me and sent
them in the mail. Other people said they are good for casting tubes but I haven't gotten
the air bubbles to clear out of them yet. Maybe it's the distance the bubbles have to travel,
I don't know.

I also had a terrible time getting the resin out, whether Alumilite or PR. And that was with
release, too. Had to use a hammer and dowel .. and that pretty much made the parts
unusable..

But others seem to have done fine with them, so it must be me

[tea lady]

I had the hardest time finding those .. in fact, another turner found them for me and sent
them in the mail. Other people said they are good for casting tubes but I haven't gotten
the air bubbles to clear out of them yet. Maybe it's the distance the bubbles have to travel,
I don't know.

I also had a terrible time getting the resin out, whether Alumilite or PR. And that was with
release, too. Had to use a hammer and dowel .. and that pretty much made the parts
unusable..:? I thought they would stretch off to a certain extent. :shrug:

But others seem to have done fine with them, so it must be me

Not that I've actually tried it. Might though! Its got me curious.:cool:

[joe greiner]

I'm still very much in the dark about your mould material. The silicone sealant/caulking I mentioned is also available in a high-temperature version for stovepipe encasement. I've made very flexible moulds for casting molten lead successfully; even the ordinary stuff works, but not as well. I haven't used it for casting resin, so I don't know how well or poorly it would release. Sprayed bond-breaker wouldn't hurt.

To cast twelve reasonably identical blanks, it might be simplest to make thirteen or fifteen walls of paraffin wax in a constant thickness, and arrange them to form twelve chambers. If the casting envelope isn't big enough, separate pours might be needed. The wax can be melted for release and re-use. The wax won't begin to melt until the resin starts to cure, so the shapes won't be compromised.

My newer scroll saw has a built-in huffenpuffer. But I'll try to remember the baby enema for any other applications. Thanks, TL.

Cheers,
Joe

[BoomerangInfo]

I'm still very much in the dark about your mould material. The silicone sealant/caulking I mentioned is also available in a high-temperature version for stovepipe encasement. I've made very flexible moulds for casting molten lead successfully; even the ordinary stuff works, but not as well.

I'm using special purpose moulding silicone designed for casting resins. I had thought about trying wax a few times, but wanted something more permanent.

Russell.

[joe greiner]

Thanks for the clarification, Russell. I guess you have it under control. I have too many other dead horses to beat, so I won't need to beat this one. :wink:

Cheers,
Joe