Torn RTV Mold

[dave2-8-0]

A little help please!

I've torn a RTV mold, and wonder if there is a good or proper way to repair it?

Dave Taylor
New Mexico Northern RR

[WoundedBear]

If the tear is in a corner try skim coating a little fresh RTV in there with a brush and squeeze....might need to clean up inside a little. Molds have a definite life cycle, and there does come a time when you have to toss it and make a new one.

I know.

Sid

[Seasaltchap]

Dave2-8-0 : I am interested. Are you pouring metal or resin.

RTV will bond to itself, it is in the warnings when making the cope: to not bond the two parts of a mould together!!

If metal, what temperatures are you working. Generally RTV is only good to about 500F, and the more you hit that, the shorter the life of the mould.

Are you putting any strengtheners within the RTV to hold it together better, like canvas or heavy cloth - and pieces of wood where appropriate to still allow release of the cast.

Regards

[dave2-8-0]

Seasaltchap

Thanks for the reply,

I'm casting 1:20.3 ARCHBAR trucks (side frames and bolsters) from 180deg CeroBlend metal.

I got tired of paying $90 for trucks, to put on a $15 scratchbuilt car.

Dave Taylor
New Mexico Northern RR

[Mike]

Dave- I enjoy molding. I've been using tin bizmuth and getting some great results. If I had a master to make a mold from, I'd be happy to give yours a try. I've been making O scale trucks for a friend here in Richmond, Virginia, for a few years now. The one thing I'd suggest is that you find some small bronze bearing blocks to place over the axle ends. The tin bizmuth makes a plenty strong truck structurally, but the wear point for the axle tends to wear too quickly.- Mike

[Seasaltchap]

Dave 2-8-0 : I congratulate you on having a go. This is the spirit that makes for a hobby.

Mike : There is no need for you to run axles in the tin/bismuth castings. There are brass bearing cups available for "O" gauge that you can drill out for, and press into the castings. Look for Item 7M63 in http://www.scalefour.org/ag/7ag2.htm

Have either of you considered doing the artwork for etched brass parts to make your kits.

Regards

[dave2-8-0]

Seasaltchap: I haven't ben running these trucks long enough to notice an wear pattern yet but it seams that Mike has. As I have to drill out the axel holes anyway, drilling larger, then pressing a brass insert in is little extra work.

As a Pro Photog I have all the hardware and software to design and make the masks for etching.  Meny years ago wile working in a Gov. research lab I had the need to make a few etchings and some parts thereof.  I haven't thought that I had the need to go there.

I would like to find out about the bushing before I make the next batch.

Dave Taylor
New Mexico Northern RR