Material for casting mold masters

[dingwall]

I'm going to try casting parts using Smooth-Sil silicone rubber for the female mold and either aluminum or plastic for the male portion of the mold.

Any suggestions for a suitable plastic sheet for the male portion. It will basically be a plate roughly 12" square, 1/2" - 3/4" thick with raised "washers" machined into the face and 1/4" dowel pins pressed into each "washer".

UHMW comes to mind, but I've never been able to rout that stuff cleanly.

[stevem]

UHMW machines beautifully. It also doesn’t stick to most resins. Use regular carbide wood routing bits with straight flutes. A feed rate of 100 IPM and spindle speed of 12000 rpm should work nicely. You will probably get a slight burr that can be removed with a knife or metal burr removing tools.

[john_david]

Another material you can use is a urethane call either wrenform or wren shape.
It machines GREAT and sands very easy. There is also machinest wax you can buy in block, machine it and melt it down and reuse it. Silicone rubber will not stick to anything so your Mother Mold can be made of anything that can be machined easily and finish sanded easy.

Thats my 2 cents

JD

[Brady Watson]

John,
I believe that you mean Renshape (http://www.freemansupply.com/RenShapeModelingan.htm) This is great stuff, but a little pricey.

I do not recommend using the machinable waxes on the Bot. They get all over the place and have an affinity for rails and v-rollers...You will be pulling this stuff out of the ways for months...ask me how I know.

For mold masters where dimensions are critical, I recommend using Renshape or similar tooling board or Rayite 100 (http://www.gypsumsolutions.com/NewsCenter/news/tooling/cs_cessna.asp) available thru ChemBar (http://www.chembar.com/allproducts.htm) if you want to save some money.

For others reading this thread, here's some extra info to help you in your material/mold making choices. The idea of making molds for casting liquid materials comes up a lot. Here's what I have found:

If you are looking to do decorative castings then you can make the master out of nearly anything (don't use foam...it floats in the rubber!) This can include MDF, Trupan, wood, rayite etc. Then seal the master and make a mold from the master. You will get a better mold by creating the master and not the mold itself on the Bot.

Few designs lend themselves to rigid molds, so if you have surface detail and a part with undercuts or straight walls, you will never get the parts out of a rigid mold that you machined on the bot. Make the master on the bot. Use rubber to create the mold. This will give you flexibility to demold the part, and the ability to capture surface details without them staying in the mold...

-Brady

[john_david]

Brady
Thanks for stopping me from making a mistake and it sounds like months of cleanup !!!
I have been waiting for an excuse to use wax and I am glad now I havent yet found one,
Sounds like you did
Your mold versus master post is right on the money

JD