Hi,
I would like to when making a mold using RTV rubber,what is the space between the master piece and the wall of the form that holds the RTV rubber? Does it matter how big/small the master is when making the mold? I have 3 pieces that I want to make a mold of,and they are,
1. 1in x 1 in x 4inches
2. 3in x 5 in x 3inches
3. 3.5 in x 5 in x 4inches
I hope you can help me with this.
Thank you.

Do you plan on having an auxiliary mold box? If not try to leave at least a quarter to a half-inch around it depending on the amount of detail on a given wall, near the outside. Any less than that and you're likely to have warpage.

Hi Jody,
For a mold that size, I would leave a minimum of 1/2 to 3/4 inch border all the way around and about an inch on top (bottom once you turn it over).

Jesse

Mold boxes can be built with LEGO-bricks
A fellow railroad modeller made very thin mold walls and then made a supporting cast with plaster. Just need to make sure that the outside shape of the silicone mold doesn't have any undercuts.
/ Robin

If you have a Hobby Lobby close use the alumilite Rubber type 3 sells for $29.00 with the 40% off coupon a good deal, after you take the discount off.
Plus besides legos one can use scrap Plastic plexiglass.
But the legos are cool also.Best place to get resin I have found is Smooth-on. try 322 I think a 30 minute set pot life, but one has to remember if not a vacuum applied,to the rubber, and pressure applied during the set process details might suffer.If you go to Smooth-on plenty of info there, and Yes I have cast a bunch of stuff, in 1/6 scale mostly.But some in 1/35 also.

https://www.smooth-on.com/


Cheers

Jeff