RESIN MASTER MOLD QUESTION

[RNfanDan]

From what I've read so far, "masters" for a resin batch are not discussed much, at least as far as what material they are made with. Can a master mold for a resin batch, itself be made of resin?

I ask, because I wish to produce a mixed-medium master hull form, which will contain styrene and metal (either brass or aluminum), but with a significant amount of resin. Once the first hull is cast, I will need to re- work it a bit, then make a second mold master for the final run (about six altogether).

This is NOT for commercial purposes, I wish to make enough only for my own interests. Thanks!

[Jean-Paul Binot]

That is exctly how masters are engineered. The initial master is in fact a pre-master made of any material or mix of materials that is handy to use and sturdy enough to stand the dip in the mold material.

Then a master is made from the resin copy of the pre-master, that is much easier to work because it is a single material. For example, PE doors and hatches are much easier to attach to resin than to balsa.

When ready, a new mold is made et voil�.

[Tom Kristiansen]

When you have made your pre-master, chop up your old RTV (Mold rubber) and use it as filler for the new batch of RTV to make your new master. RTV sticks to RTV. You save a lot of expensive mold material and your operation is suddenly far more cheaper than making two fullsize pre-master & master molds. Just make sure no voids or airbubbles are left in the new RTV.

(You have probably thought/heard this before, but I mentioned it just in case you didn't.)

[scratchshipnut]

Ditto to what Tom says on rtv peices. I pour the new rtv then add the slices on the side to displace volume and raise the level of the rtv. Try to slip the peices in to avoid making bubbles. And yes I've made molds from a resin master too

[RNfanDan]

Thanks, gurus!

I have never made a mold in my life, for resin model casting. The first "run" I want, are destroyer hulls of German 1936A type; I had planned for three of these, in ready-to-build condition. Accordingly, I thought I'd cast four, saving 3 and using the fourth as my re-workable master for a second mold, a batch of three 1934A type hulls.

Based on your responses, it looks like I'd better plan to make a total of FOUR molds, not two. When I wrote of re-working a resin casting made from batch of 1936A's, I was thinking of more substantial changes (hull dimensions, contours, etc.) to suit the smaller 1934A's.

Rather than having either to modify my original mixed-media hull, or start all over with a fresh 1934A mixed-media hull, I thought it easier just to re-work an extra resin hull cast from the first 36A batch (hence, my original question).

Is it considered "normal" to make two molds (or more) per batch run of a given model? If so, how much improvement over the "pre-master" is to be expected?

My apologies for this, but as I stated, I am a total newcomer to resin molds!