I have two simple parts that are “missing” from an out of production kit. Unfortunately scratch building the missing part out of the question as it has close tolerences and requires a some strength.
Luckily I have two of the same kit, so I have access to the original part. I would hate to call the kit a wash since it’s getting rare and $$$.
My question is this:
Can I make a negative mold from a master. Then make a copy using some sort of resin?
What would you use for the negative? Would Sculpty baked clay work? Would I cover the original in oil or flour? And what material would you use to form the positive?
~Thanks
~D
Here is some info on casting. Alumilite is one product that could be used, but the methods apply to otther products as well.
http://www.alumilite.com/howto.cfm
Is it a complicated part? Sculpty will work for simple shapes, but getting a nice copy out of a mold can be difficult.
A silicone rubber mold would probably be the easiest, you need to put a little effort into getting the mold right but you can make 100% exact copies with one. You can use Aluminite, I personally have had really good luck with Smooth On (www.smoothon.com).
They have a starter kit with the mold rubber and the resin for about $25 . And they have excellent information available, both included with the kit and online.
Alumilite, Smooth-On and a surprisingly large number of other companies sell materials to do what you want to do. You’re looking for polyurethane resins for the cloned casting and RTV rubbers for making the mold.
You should be aware that there’s going to be a small amount of shrinkage ( a few percent ) in the resin casting. The manufacturer’s site will be able to provide the exact amount of shrinkage involved. Unless it’s a part that’s involved with the mechanism in some way, you probably won’t notice it.
-Ed
Micro Mark has a molding rubber and urethane casting material. The bad news is the rubber runs around $30 for a quart and the urethane @28 for a quart. The stuff lasts quite a while after being opened. I don’t know what the shelf life is but I’ve had opened containers sitting around for about a year and the stuff still worked.
From your original post “close tolerance” and “strength” is likely not going to come from a resin cast part. It sounds like you are trying to do a mechanism part (gear?connecting rod?) and that is not going to be possible. Resin parts of small cross sections are very brittle.
I’ve cast my own parts a few times. I did it like this.
First I make a mold of the part using heavy aluminum foil (not the cheap stuff). Burnish it down good with a Qtip or something. This can be a two part mold (for a 3D type part) or a one part mold (for a 2D part). Then I mix up some 5 minute epoxy (i use Devcon brand, but any should work) and fill the mold. I usually go have lunch or watch a TV show or something, then come back and remove the part from the mold. I wait 24hrs. for the part to cure fully before any sanding or painting.
The part can be a little tough to get out of the mold, but I’ve heard that you can spray the inside of the mold with Pam cooking spray and that fixes that, but I haven’t yet tried that.
Hope this helps.[8D]
Better be careful about “cloning” those parts. You may receive offers of funding from private interests groups, but incurr the wrath of strong conservatives. Then the Sith may take over and turn your layout into an evil Galactic Empire which could take decades to overthrow. Sure as that happens some guy will come in and make a series of movies about it and mae hundreds of millions of dollars all at your expense. You will then be forever be dubbed the initiator of the Clone Wars.
[(-D] [(-D] [(-D]
Ron
RTV (room temperature vulcanising) rubber is your best medium to make a mold for resin castings.
Easger Plastics in Chicago has great stuff as well as Vagabond Corp. in California.
There is no “t” in Sculpey, read the box (sorry pet peave there)
Sculpy is only ok for low tolerance, fully drafted parts. And you have to use some sort of mold release that will not hinder the resin from curing nor affect the surface texture of the resin part. Plus you may end up chipping the mold trying to get the first part out, then the second part will have more cleanup and so on.
I highly recommend you learn rubber & resin, it is vast in it’s possiblities.