How is everybody duplicating molds??

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How is everybody duplicating molds??

Postby Anvils Hammer » Sun Oct 09, 2011 2:10 am

So we all know how to make a mold...

Once you've got that mold, and need production molds, how do you go about duplicating the original?

I put the mold in a box and pressure cast resin over the top, so I get a solid resin block which I call a "mold mold". turn it upside down, pull out the master molds, pour in rubber and pressure cast again.

Repeat to make production molds and when molds weat out and need replacing.

Ive had a few problems with resin shrinkage distorting the mold mold, but largely solved that with slate filler and a ridgid bottom plate. My production molds come out about 98% the size of the master mold, IE not noticably smaller.

I was just wondering how everybody else went about this task?

Cheers,

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Re: How is everybody duplicating molds??

Postby mangozac » Sun Oct 09, 2011 9:48 am

I currently do all of my moulds as Single Part Split Moulds, which doesn't facilitate using mould plates (as Jon Paulson calls them). But for 2-part production moulds they are definitely the way to go!

We did have some discussion about it a long time ago (and may have had further discussion since). Using a slate filler to minimise shrinkage is a good idea, however 2% still sounds like a lot. There must be minimal shrinkage resin products you can get solely for making the mould plates?
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Re: How is everybody duplicating molds??

Postby blind pig » Sun Oct 09, 2011 11:12 am

mangozac wrote:Using a slate filler to minimise shrinkage is a good idea, however 2% still sounds like a lot. There must be minimal shrinkage resin products you can get solely for making the mould plates?


I have seen mould moulds using a platinum catalyst silicone to mould a tin catalyst silicone, and gave it a go myself, but I really don't need to have mould moulds, so don't bother. As with Mnagozac, most of my casting is a split mould or a two part mould when I'm feeling like it.

As to the shrinkage, 2% does seem a lot, but I guess, after the first cast from the mould mould, all your moulds would be at 98% original size and for production and would all be the same size and that difference not noticeable or important, except if you were to put parts from the original mould in with bits from the mould mould mould (as it were) :lol: .
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Re: How is everybody duplicating molds??

Postby paulson games » Sun Oct 09, 2011 7:14 pm

I use the plates or Mold Molds. There may be a tiny bit of shrink but it's really hard to tell. Once I create the resin plate I run all of the molds off of that from then on so each copy is more or less the same.

One a few of the molds I've noticed that I have to rubber band it slightly more than the original or it gets extra flash, I suspect this is due to the minute shrinkage of the resin and silicon vs the original master. The easy fix is just wrapping the rubber band around an extra time or adding more bands.

They tend to work out really well, just take care not to break them. If you didn't save the original master then you have to start from square one again.
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Re: How is everybody duplicating molds??

Postby Anvils Hammer » Mon Oct 10, 2011 9:46 pm

Its great to know that rubber bands are considered the state of the art tech to use by other people!

Yeah I have looked for low shrinkage resins but there doesnt seem to be many.

For parts of the scale I make, 98% is not disernable by eye, and the master mold only makes 30-40 copies before getting thrown away anyway.

I know this means I have to take extra care of the mold molds, but I do.. and so far Ive periodically remade most molds anyway, to improve the quality of the masters.

the split molds article is interesting. Its somthing Ive never tried.

It seems like they would work well, but only If I could make a mold mold of it- Im thinking it would be perfect for helmets. I could fill it, then pull the sides apart, deliberatly creating a thin layer of flash. I then remove the master, leaving the flash in place. That way I might be able to pour further molds and the "split" is automatically created by the flash. The product molds being banded together removes the flash..

I will experiment next time I get a part that would benefit from that.

Ive experimented a bit with molding parts from a single vent at the top and met with complete failure.. hence I alway run the resin in at the bottom and out the top.. I guess if it works for other people I just need to practice more...

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Re: How is everybody duplicating molds??

Postby mangozac » Tue Oct 11, 2011 7:51 am

I just looked up the datasheet, and the 4PU resin that I use (which is a pretty standard, off the shelf product) has a shrinkage of 1% unfilled. So adding some filler in I would expect no discernible shrinkage at all. Not that 2% will be all that noticeable.

Honestly 30-40 pulls from production moulds is pretty poor, especially since none of your parts look to be that hard wearing on them. I really think you need to have a good chat with the supplier and track down some better/more suitable products.

Split moulds was a technique I was taught by a professional caster a couple of years back. It works really well for smaller parts (even the size of an entire figure) and according to Blind_Pig that's the same technique FW uses for much of their stuff. Making plates for the split mould I'd never really thought hard about but I guess it's possible as you describe...

Because there's only the one gate for both resin entry and air exit in the split mould, it helps to have a vacuum+pressure casting setup like I have, however I think by squeezing the mould in and out while pouring the resin in most of the air can be expelled.
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Re: How is everybody duplicating molds??

Postby Anvils Hammer » Tue Oct 11, 2011 8:34 am

The other advantage of a split mold.. it presumably holds itself together without a need for elastic bands.. which would rock..

mangozac wrote:Honestly 30-40 pulls from production moulds is pretty poor, especially since none of your parts look to be that hard wearing on them. I really think you need to have a good chat with the supplier and track down some better/more suitable products.



30-40 is what I thought I was getting..

I've just finnished a production run for a client, which for the first time has allowed me to test exactly how many pulls Im getting.
The part was fairly complex but not amazingly so. Ive been getting 25 good pulls, with an extra 5 pulls if I dont mind easing it out of the mold.

And yeah.. its pretty shocking.. which is annoying as im otherwise very happy with the rubber. Ive got another sample from a different company I might try out.

Im currently using T28 TRV silcone from tiranti.co.uk-
http://www.tiranti.co.uk/subdivision_pr ... vision=175

If any of you guys have suggestions for UK RTV silicones that I can get 40+ pulls out of, please link me!!

Cheers,

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Re: How is everybody duplicating molds??

Postby mangozac » Tue Oct 11, 2011 8:55 am

Anvils Hammer wrote:The other advantage of a split mold.. it presumably holds itself together without a need for elastic bands.. which would rock..

Oh no don't get confused - you still need elastic bands and ideally boards on each side as well. The boards help distribute the pressure evenly to minimise the flash.

Some of my BFG models are really hard on moulds, as there's lots of spots for the silicone to get stuck in. When I was using the tin catalyst silicone I was getting about 30 pulls and now with the platinum cure I estimate 50 to 60. If I was doing mass production I would modify the models, particularly in the spots that tear the mould first.

Not being in the UK I can't really help you out with a recommendation: like I said, your best bet might be to talk to the supplier/manufacturer. Tell them you are planning to ramp up into decent volumes - give them a reason to convince you to stick with their product ;)
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Re: How is everybody duplicating molds??

Postby Fleafa » Sun Jan 29, 2012 10:43 am

Anvils Hammer - I started with Tiranti for rubber and resin but there are better places out there. I'm currently using RTV and FastCast PU from CFS Fibreglass. Nice guys on the phone and competitive prices. About to order some resin from Alchemie though. Will let you know what I think.
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Re: How is everybody duplicating molds??

Postby Anvils Hammer » Mon Jan 30, 2012 8:51 pm

Ill check those guys out

Im not with tiranti anymore.

Curerntly getting rubber from Bently Chemicals, Ive run 30+ casts with my cloak molds with their stuff and no sign of wearing out yet, compared to maby 25-30 casts for tiranti T28

Resin Im getting from John Burn. £10 a kilo plus vat/delivery. Best price ive found so far for quality stuff.

EDIT- damn.. CFS are even cheaper.. gonna test that out for sure!

Ill keep experimenting..

I cant wait till my volume is high enough to use 5kg cans instead of 1kg.. will reduce resins costs by 30% overnight!

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Re: How is everybody duplicating molds??

Postby Fleafa » Mon Jan 30, 2012 11:42 pm

I would say beware of CDS FastCast. Quality is fine, but pot life is 1.5 to 2 mins!
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Re: How is everybody duplicating molds??

Postby Anvils Hammer » Tue Jan 31, 2012 1:02 am

I bought a 2KG kit, cost £30 in total.. but £11 of that is next day delivery! Im impatient!

Ill be testing it out tommorow and report back..

Short pot life doesnt bother me that much.. I like to think after almost a year of casting almost every day im pretty fast at moving molds around!

For my purposes, the shorter the better, as demold within 20 mins is awesome for turning the molds round fast!

At some point though im going to try out a long cure resin-

I tried FC10 from Jacobson, dont remember who recommended that to me, i like it a lot, great strenght and flexibility, but it takes almost an hour to set up which is no good for me at the moment.

In future though it will be worth using it or something similar, as in the 7 minute pot life, I can vacuum pour several plates one after the other, before putting them all in the chamber..

When my volume is higher I suspect Ill have 2-3 resins "on tap" which I use depending on the situation/mold.

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Re: How is everybody duplicating molds??

Postby Anvils Hammer » Thu Feb 02, 2012 10:25 pm

got the CFS fast cast..

It stinks! the odour is overpowering.. My respirator cuts it out obviously but i take it off and room feels bathed in chemical.. other resins ive tried hardly smell at all unless im currently working with them.

The pot life is really short like you said.. the viscosity is initially really great, but rapidly becomes more treacly, the effective pot life is shorted than advertised.

I mixed in my metal filler etc to make my gaming base resin.. the other day I poured this into a "bike" base split mold and the weight of the resin pushed the air out no problem. Today I tried the same trick with a 25mm mold and it didnt work.. had to squeeze the molds to get the resin in.

It could be the resin.. or the size of the bases, or the vents being slightly smaller.. I dont know. but I need to figure it out so I can re-release my bases!

Interestingly, the CFS fast cast bubbled a lot less in my vacuum chamber.. im going to go and open those molds in a bit and see how its worked in the vacuum chamber..

I also need to test pouring my gaming bases in the vacuum chamber, as Im hoping those will "work" without pressure being needed, due to the high filler content and weight of the metal in the resin.

I really must get some photos of all of this!

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Re: How is everybody duplicating molds??

Postby Anvils Hammer » Fri Feb 03, 2012 12:05 am

bah!

It worked wonderfully! which is really annoying.. I vacuumed 11 split molds, 55 components in total, there was ONE blemish that was so tiny I hardly noticed it.
More tellingly, a couple of "torso" molds worked flawlessly, I had been planning on redoing them because with my normal resin, I was consistently getting an air bubble in the same place each time on each torso.

compared to G27 LV, my regular resin-

Pros- 100% perfect components, compared to air bubbled in various parts of some molds.
-cheaper, £17 per kilo instead of £20
-initial tests show its not brittle

cons-
-horrifically strong chemical smell fills the room
-pot life is very short, means Im a bit rushed..
not as nice a finished consistency,a bit more oily/translucent.

The viscosity and cure time are similar to the G27 LV.

I want a resin with the price and bubble free qualities of the CFS resin, but with the finnished part consistency and ease of use of the G27..

the search for the perfect resin continues!!

What really annoys me is that I dont know what it is about this resin that makes it so much better..

Im going to crack open a totally new set of G27 and see if it was "old resin" that was causing the problem..

Side note- if you mix filler into resin.. degas the components separatly rather than when its all mixed and in the mold.. there was much foaming!

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Re: How is everybody duplicating molds??

Postby Blindhorizon » Mon Dec 03, 2012 3:12 pm

I'm 100% noob, but I'm reading this and i find myself asking, what is filler? Now I'm not slow or dense so I'm assuming it's a product to add to resin thats cheaper then the actual resin? I ask here because my question came from reading this thread, if I'm posting in the wrong spot my apologies.

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