some notes on Resin Casting

[JESTER]

Great stuff John! I've only used foam-core to make the mold box. Vaseline is a great silicons to silicone mold release.

I use talcum powder for mold release when I cast up the resin parts.

HERE's some progress shots of a mold I made.

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[gin sot]

It's really nice that you're thinking of your customers.  But it seems to me that anybody who spends over a hundred bucks on a resin kit of an obscure bridge is playing under big-boy rules and should know to clean the castings before working with them.  Removing mold release agents is a basic step when dealing with parts, be they fancy cast metal or resin, or just a six-dollar injection-molded styrene kit.  The less you as a manufacturer have to dick around with remaking molds with expensive time and rubber, the lower your cost will be, which should lower the selling price, which should mean more people can afford a really cool model kit. 

I typically re-wash any parts or subassemblies I've so much as handled with bare skin with detergent and a toothbrush before I paint them, and I've been doing it since I was a kid.

[JohnP]

Trouble is my parts are thin and fragile. Any kind of scrubbing will break them. My goal was to make the kit accessible, not a frustrating struggle. So the mold release was a big issue. I had hoped to ultrasonically clean them, but the material manufacturers stated that mechanical action was needed. Plus, I would have needed a pretty big cleaner for the long parts. The spray needs to be applied very sparingly according to the instructions, then it is undetectable on the part. It will work for most; for others they may wish to clean a bit if they deem it necessary.

And boy, I tell you what, don't suggest to any D&RGW modeler that the bridge is obscure- I have had plenty of interest and decent sales for my very part time project. Made it all worth while, enough so that I am moving on to my next bridge.

Thanks
John

[Philip Smith]

Good deal John. Price Driscoll will supply samples if you ask and there product is rotated frequently. I purchased some PD from another company (old stock) that contained ozone depleting materials from way back. I'm not saying your supplier sold you some bad stuff just a FYI and you may call PD with the lot number if necessary or request a sample.

It is odd that the molds are swelling. It must be a combination of force, casting resin and a reaction to the aluminum frame. Never worked with the platinum stuff  Weird stuff, glad your getting more pulls now.

I noticed a x-brace on page 2 of this thread. Are you casting the turnbuckle and rod?

Philip

[JohnP]

Philip, the swelling occurred with the first styrene frames, so we can eliminate the aluminum factor. I was aware of the contact areas becoming hardened but that was to be expected. Apparently the resin byproducts permeate the entire body of RTV. That may be enhanced by the pressure casting. I could try different resins that are less harsh but the material I use always hardens in thin sections whereas some don't.

The PD spray is the latest material. I am very happy with it indeed.

I really haven't decided on much of the rest of that little bridge. I would hope to buy correct size turnbuckles to save me the trouble. I have been working on filling orders for the D&RGW truss. I have little time for hobby projects in my hobby business!

John