Need resin casting help? Ask me.

Yes it is nice to be able to put your projects INSIDE something isn't it? You know, to hold everything together so it doesn't flop around? Discuss the techniques here!

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Galane
Posts: 17
Joined: Sat Feb 04, 2012 4:28 am

Need resin casting help? Ask me.

Post by Galane » Sat Feb 04, 2012 5:30 am

I've been making RTV molds and casting resin in them since circa 2004. My business is replica lenses and other plastic parts reproductions for classic cars. I'm always willing to share knowledge learned from my experience, to help others avoid the problems I encountered learning this stuff.

I also do spin casting of light metals in silicone molds and I've done fiberglass molds and plaster molds for ceramics - in addition to tons of other things one learns when yer either too broke, too cheap, or too perfectionist to pay someone else to do. ;)

What I won't/can't do - make molds or cast parts for you. I spend my work time making molds and casting parts for my business. Current project, restoring a large hunk of plastic for the dash of a 1934 Graham so I can make a mold for casting a couple of new ones.

If you want to make high quality molds and castings, here's an equipment list.

1. Pressure pot. Harbor Freight has one that's inexpensive and good enough. (Needs easy modifications for casting instead of spraying paint.)
2. Air compressor capable of raising the pressure in your pot to 60 PSI in a couple of minutes or faster.
3. Dremel or similar rotary tool with fiber reinforced cutoff disks and various mounted points. (grindstones) Not a cordless one or one of those wimpy DC ones that power from a wall wart. Only the AC powered ones have the power to cut the silicone.
4. Sharp knives and a good sharpener to keep them really sharp.
5. A supply of corrugated cardboard that's shiny on one or both sides. Used priority mail boxes are ideal. RTV won't stick to this type of cardboard.
6. Hot glue gun and glue sticks. Use with the cardboard to make mold forms quickly and cheaply. Forget L-boards and everything else you know about making mold forms. Cardboard and hot glue is way easier and will fit in the pressure pot.
7. Flexible funnels. I use small ones made by LuMax because they're easy to remove cured resin from and they last a long time.
8. A solid plastic or metal cylinder, about 1" long, of a diameter that your funnel will fit snugly into a hole that diameter. This is for use as a sprue former.
9. Sulfur free plasticine modeling clay like Klean Klay or Crayola modeling clay (formerly called Clayola).
10. A coffee mug warmer and a junk ceramic saucer for softening the clay. Makes it much easier to work with.

On silicone, I only use platinum cure RTV for making molds. Almost all resins will cure against it and it has essentially zero shrinkage. Platinum cure molds have a very long life when taken care of. Tin cure RTV is slightly less expensive but causes cure inhibition in some resins, has higher shrinkage, has to be heated to finish curing before making castings and will deteriorate over time. Can't make a tin cure RTV mold and expect to pull it off the shelf years later to make more castings.

Galane
Posts: 17
Joined: Sat Feb 04, 2012 4:28 am

Re: Need resin casting help? Ask me.

Post by Galane » Sun Feb 05, 2012 5:25 am

Here is Day 1 of the process of making a RTV silicone mold.

http://partsbyemc.com/pub/mold-making.htm" onclick="window.open(this.href);return false;

I'll be finishing this up over the next couple of days.

Edit: The mold is completed. Go to the link to see the rest of the steps.

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