Investment Casting Master Pattern Creation

Scott,

If you're going to use vulcanized rubber molds, most patterns are made from metal.  Brass come to mind but it really doesn't matter.  The primary reason is, the vulcanizing process uses heat and pressure.  Plastic, or resin parts, can't withstand either.  Typically, you need to add 5 to 5 1/2% for shrinkage.  In other words, if you're going with vulcanized molds your patterns need to be oversized.

If you use RTV (room temperature vulcanization) you can use plastic or resin parts because there is no heat or pressure used in the creation of making the mold.  Depending on the RTV used your shrinkage will be 1/2 to 2 1/2%.

There is a whole lo more to the overall process but we can go into that later.

Jay

I might add that your second option works, with an additional 1/2% shrinkage.  You make the part in plastic or wax, the foundry uses that for a one-shot brass part, you look that over and add brass (in my case journals and brake hangers), and the foundry makes a rubber mold of that.  My PA truck (not nearly as good as CLW, but acceptable) was done that way.

Thanks for the feedback.  I 3D modeled up a brake wheel and gear assembly, so now I have to get some machinable wax and attempt to CNC machine the individual components; gearbox, wheel, and release arm (although I may just try to hand make the release arm from brass).  I have to get some itsy bitsy end mills though.  Funny how the smaller the end mills get the more expensive they become .  I think I'll start with the base gear box assembly as that is the simplest to machine but still has some small details and contours to work around.

Scott

Ambitious project!  I just grab an old stamped wheel and stamped gearbox and pin it on.  I will never join the ranks of true scale modelers.

You sure you shouldn't try something a tad less intricate, for a first attempt?

There are UV resins used in DLP 3D printers that can be used for investment casting. I am no expert and only learned of these recently from a friend but have found examples. Here is one. Resolution from these printers is an order of magnitude better than filament printers for comparable prices.

Pete

Hi Bob,

Actually, I will start out with a dumbed-down version of the gear box assembly to keep it simpler and then add the NBW castings and a gear mockup later as a second step - not yet sure if I want to make these add-on parts in brass and solder to the brass casting boxy or make them in wax and have them present for the original casting.  All-in-all, neat stuff....

Thanks Pete DLP casting resin link.   The 3D printing technology  seems to be advancing at all levels.  The professional direct to wax 3D printers used in the jewelry industry were amazing in the level of detail they could print but it still came at a monster cost.  They use an additive and subtractive method (3D print wax layers (additive) and then machine off (subtractive) enough to make each layer super smooth and  uniform for the next layer to be printed which leaves a homogeneous precision wax pattern when it is all done.  They are doing to same additive / subtractive methods with metal 3D printers as well to get precision parts from 3D printed methods - especially cool when multiple metals are used to make something that cannot be done with conventional methods.  For example, I could 3D print this gearbox housing in brass but also print a full outer coating of titanium for added "corrosion resistance" .

Scott

Scott,

If you email I can offer some advice.  I have thousands of rubber molds and have many castings done every week.  I've found, over the years, trying to sort through all of this on forums rarely works out.  Too many people offering advice that don't know what they're talking about.

Jay

Scott, a friend has this printer sent me a link to a youtube video that demonstrates its capabilities. I have found it for as low as $510. The downside compared to filament printers is the resin is pretty pricey. Not sure you could get the same surface resolution with machine tools though no matter how tiny.

https://www.youtube.com/watch?...amp;feature=youtu.be

Pete