Casting wheels?

[Kit Basher]

I am getting ready to make my first attempt at casting wheels. I would like to cast two at a time. Any suggestions about organizing the mold? Should the wheels be horizontal or vertical, right side up or upside down? Should the resin enter the wheel from the top or bottom, where should the mold split, etc. Any advice would be very welcome. TIA

[minitrucker1983]

I'd be interested in info on this subject also. I can't seem to get rid of all the air bubbles when I pour my resin.

[Art Anderson]

If you are casting just the wheel rims (either steelies or mags) and if they are wheel halves, you can cast them flat. To make such a mold, first I'd make sure that the back side of the wheel half is flat, so that it can be mounted on a flat surface, such as a piece of sheet styrene (at least .040" thick so that it stays flat) with a drop of CA glue (you can pop the original loose after casting up whatever wheels you need afterward, lightly sand off the remaining CA and then use the original wheel on a model if you so desire). Next, I'd box in that wheel with some .250" strip styrene, say, .040" X .250" (that's a quarter inch wide) with the strips glued on by their edges, to make a 1/4" deep mold box). Then, make a second mold box, the same size as the one with the wheel in it, but with nothing in it (this will be used to mold up a flat, smooth, 1/4" thick block of molding rubber).

Pour the rubber into the mold, using toothpicks to make sure that the rubber flows in, around, and over all the surfaces of your wheel so that there are no airbubbles next to the wheel used as the "master". This is important, as any air bubbles next to the master wheel will result in your getting resin "balls" or "goobers" attached to the castings which even if you can remove them, will mar the surfaces of the wheel castings. Pour rubber into the plain mold box, and of course, let the rubber cure completely.

Now, when you remove those blocks of rubber, you will have a cavity mold for the wheel half, and a smooth block of rubber which will be used as a cover for the cavity--once you fill your wheel mold with resin and have "chased" away any air bubbles from the details in the mold, simply lay the plain rubber block, smooth side down, on top of the cavity mold, and press firmly around the edges, to squeeze out the excess resin (be sure to press it down around the edges, NOT in the middle of the cover block, otherwise you can push the cover block even slightly down into the cavity, and when it springs back it will suck air into the mold, making a bubble or "void" in the back side of your wheel castings). But, doing this extra step, with a bit of practice, should give you wheel halves that will look just like the original, but with very minimal "flash" around the edges of the rear (inner side of the wheel half) to remove--in addition to the wheel half castings being flat and true on their back, or inner side. (I cast tens of thousands of wheel halves, including wheel covers and dog dish hubcaps in this manner during my time in professional resin-casting of model car parts and transkits--so I know it works, and it is simple to do.)

This method works with the more modern model car kit wheel halves, but if you are working with wheels or outer wheel halves from older kits with wire axles, then you will need to make a full two-part mold--which I can describe to you here if you need me to.

Art

[Art Anderson]

I'd be interested in info on this subject also. I can't seem to get rid of all the air bubbles when I pour my resin.

As I noted just above, this is where toothpicks come into play! You can use a toothpick to "chase" those nasty little air bubbles away from the surface of your mold. However, you do have to do it fairly quickly, as most polyurethane resins have a pot, or working life of perhaps 90-seconds.

Art

[Kit Basher]

Thanks for the reply, Art. The wheels I want to cast are halves, but they are not flat on the back. Here are some pictures:

The back:

The front:

I guess I would need a two part mold, any suggestions for that?

Edited August 12, 2013 by Kit Basher

[Art Anderson]

Hugh,

I'll work through this with you by PM over this coming weekend, when I have more time to devote to it.

Art

[Kit Basher]

Thanks, Art.

[Chief Joseph]

Hugh, here are a couple of photos that might help illustrate how I make two-part wheel molds:

The basic idea is to attach sprue blocks to the tops & bottoms of the wheels and connect the blocks at the bottom with a runner. As you pour resin into one hole, air is pushed out the other hole. Ideally, you would use a third pouring channel that allows the resin to drop to the bottom sprue and fill each cavity from the bottom up, but I'm frugal with my silicone.

Alternately, you could forgo the sprue blocks and use a squash mold. But then you'd be wasting resin, making big flash layers in your wheel holes, and throwing out about 25-30% of your castings because of trapped air bubbles.

[Kit Basher]

Thanks, Joseph, those pictures answer a lot of my questions. You're getting beautiful results. The only wrinkle I see for the wheels I want to cast is that there is a rim around the outside of the wheel. I guess that I would have to make the molds separate at that rim, in order to get the wheels out of the mold, but I run the risk of having flash right where I don't want it. It looks worth a try, tho. Thanks again!

[Lownslow]

im liking that set up is it pressurized