Masters for remolding

[wormwood]

I think that it'd be a really good idea to save the first resin cast from each mold, for the purposes of making more molds later. This would enable you to make subsequent production runs, rather than being limited by the service life of the original mold.

[mangozac]

I think most of us already do this. In fact some make special resin "mould plates" that are negatives of a two-part mould so that making new moulds is simply a matter of pouring silicone into the mould plate.

[Fleafa]

Zac, could you elaborate on the mould plate concept please?

[mangozac]

We discussed it a bit in . And . I personally don't do it but I know Paulson uses the technique.

[Fleafa]

Oops, did a Google search but didn't think to search the forums! DOH!

[blind pig]

I always save the second or third casting from a new mould of a new item. By the second or third pour, you should have worked out all the bugs and bubbles in a new mould.

[Anvils Hammer]

I was using mold plates.. but now that Ive started using split molds I cant see myself ever using a 2 part mold again! Split molds are just so much better..


My Procedure at the moment for mass production-

get a few different parts, make a mold, make 5 copies of each part.

Take all 5 copies of one part and put them on a sprue, from this, make a "master" mold.

Whole sprues from the master mold are then used to make production molds, with however many sprues I need depending on anticipated part volume.

The "master" mold will make at least 20 perfect copies, so if I get 30 pulls from each production mold, I can make three thousand parts before I need to re make the master mold!

The original 5 master parts go in a bag in my "master drawer" for future use!

I measured, and the "2nd generation" resin parts are only a fraction of 1% smaller.. I think the shrinkage is a lot less with smaller parts- less exotherm..

AH

[geomod]

Amen to the split mould.

Like Anvil's hammer, I'm a recent convert, but I don't see me making two part moulds again any time soon.

[factor40]

To Geo or Anvil: If you have the time, a few pics of how you cut those split molds would be greatly appreciated.

[Anvils Hammer]

sure I can do.. but err.. it would just be a photo of me holding a razor blade stuck into a cube of rubber..

so youve got your sprue with parts, attached to a lump of plasticine which is going to be the pour channel, you pour silicone over teh top.

you then have a block of silicone with a bit of plasticine on the top.. pull out the plasticine, snap the sprue bar away from the masters and remove it..

you then have a block of silicone with a trench, and at the bottom, a load of small white/grey/green rods/parts..

Using a surgical scalpel, cut down to the parts and between then, trying to avoid excessive damage. when youve cut enough, you can remove the parts, you're done!

Pulling the two halves apart while you cut make it a million times easier!

I figured it out by trial an error.. I think Mango already posted some photos of split molds?

AH

[factor40]

I guess I'm thinking the cutting is more difficult than it is. I'm curious how people approach it. No biggie.

[Anvils Hammer]

take your time, use a VERY sharp blade, and pull the mold apart, think about cutting from various angles to get into any undercuts.

Its not difficult, just dont rush it!

AH

[mangozac]

My tip: use a fresh blade. And ply apart the two halves of the mould as you do it so that as son as you touch the knife to the rubber it splits.

Apparently some of the platinum (addition) curing silicones can be fairly hard to cut (Jon found this with the stuff from TAP Plastics IIRC).

[blind pig]

buy some #11 scalpel blades and use them carefully!

the silicone does contain silica and will dull any blades really quickly.

[Anvils Hammer]

I find that..

Luckily before I started Anvil, I played around with making some bar fruit slicers, left over from that project I have about 300 industrial quality razor blades! they are awesome!!

Ill be gutted when they run out as another box will be £50!

AH