Resin Casting

[Sokramiketes]

Mike,how tough is that wax? A friend does dental work,he gave me some wax he uses for lost wax castings.I poured it in a mold,it stuck to the silicone like I crazy glued it in there!! I'm wondering if that stuff is any better.I'd like to lost wax cast pewter shells and chassis..

Hmmm... it is tough but I'm not sure how it would work in your situation. What silicone are you using that stuck to wax?  Castaldo Liquafast is a clear RTV silicone for jewelry making that I've seen used for shooting waxes.  Its the quick and dirty version of a vulcanized rubber mold... but won't last as long.  It's clear so it's easy to extract the initial part when slicing the mold open.... as you can make out where the part is and how close to center you are. 

[LV LOU]

Hmmm... it is tough but I'm not sure how it would work in your situation. What silicone are you using that stuck to wax?  Castaldo Liquafast is a clear RTV silicone for jewelry making that I've seen used for shooting waxes.  Its the quick and dirty version of a vulcanized rubber mold... but won't last as long.  It's clear so it's easy to extract the initial part when slicing the mold open.... as you can make out where the part is and how close to center you are.

The RTV was Smoothcast 322.The wax stuck to the rubber.Where do you get that wax?

[Sokramiketes]

The RTV was Smoothcast 322.The wax stuck to the rubber.Where do you get that wax?

McMaster Carr sells reasonable size chunks of Freeman's Machinable Wax.

[PJPickard]

Mike thanks for the info.
I am currently struggling with getting my small cnc up and running to make more tests.
You are on the same idea track as I am...very nice thinking and work.

Paul

[wazzou]

I finally took the time with the help of my 11 year old daughter holding the calipers, which allowed me to snap some iPhone pics and then make a collage to illustrate the shrinking that was common with Alumilite casting rubber/resin.

These pictures show an average shrinkage of .022, which is much, much greater than the .005 advertised (over 4 times).  Granted, this was a cull but typical of the worst experienced. 
On average, of the 8 cars I built, utilizing 16 side castings, the shrinkage was at a rate of .014. 

That is clearly not an acceptable rate IMO.

Having constructed the cores per dimensions with the underframe, roof and ends attached, I built the master to fit the core.  I was able to compensate for the shortcoming in the length of the sides by shimming in some .020 x .030 stock at each end which in hindsight worked out just fine.

Note: The 2nd image in the 1st row shows from top to bottom, a complete car, an incomplete assembled car, a side casting, the rubber mold and lastly, the master.
         In the middle row, image 1 shows how short the casting is of the 2.995 in. of the master.  The 2nd image in that row shows the length of the casting at 2.925 in.

[DKS]

I just measured an object I cast this morning from a master I finished two days ago. The master measures 1.587 inches across, while the casting is 1.579. The combination of mold and resin shrinkage, per the specs from Smooth-On, is .0075 in./in. Based on the dimension of the object, the calculated shrinkage should be .0119, whereas the actual shrinkage is .008.