Friday, June 12, 2015

What's in a wheel - Part 2

In this post, I will discuss how I made a mold.
 
Step 1, acquire a decent condition wheel (the plastic part) to use to create a mold:
As you can see from this picture, some of the banjo parts are broken, but the wheel is essentially intact. This wheel came off a '37, but it's the same size, so as a mold, it should work perfectly. Finding this wheel was a stroke of luck. I happened to check eBay on the last day of the auction and picked this up with no competing bids for a really low price. After I'm done, I will either repair the spokes and re-sell it or just sell it as-is and make my money back.
 
Step 2, acquire some liquid silicone rubber to make a mold of the aformentioned wheel:
For this, I opted for a product by Smooth-on called OOMOO 30. It is a 2-part liquid silicone with a fairly thin consistency which doesn't require a vacuum chamber to degas it. It's designed specifically for amateurs and hobbyists. 
 
Step 3, make the mold box:
 
 
This part was the hardest thing to consider. I was envisioning either making a square box which would waste huge amounts of silicone or require some kind of filler. Or, I would spend weeks or months making a segmented wooden box with lots of small pieces. Somehow, I never considered other materials until I saw a video where someone made mold boxes out of foam board. The dollar-store had the thin stuff which worked quite well to make a round box seen here. The hardest part of this was applying the hot glue to the bottom thick enough to seal it but quick enough to put it down before the glue hardened.
 
 
Step 4, pour the first half of the mold:
For some reason, I don't have a picture of the first half poured, but here's a shot of the first batch mixed up. You need to really stir this stuff until there are no more streaks. Otherwise, it won't set properly. Oh, and plan to have more than you think you'll need because I needed twice as much as I thought I would need for half the mold. In addition, you should also set up mold boxes for anything else you might ever want to cast in case you mix up too much. Once it's mixed, you can't un-mix it so you might as well put it to good use.
 
Step 5, apply a mold release:
No photo here. I considered different options for this. I was going to use petroleum jelly, but I opted to use some craft store mold release instead. You spray it on, brush it with a chip brush, spray it lightly one more time and then let it dry. Using this stuff was a bad idea, as it turns out.
 
Step 6, pour the second half:
Again, no photo. It's just me pouring more purple goo.

Step 7, remove the mold from the mold box:
So, if you look carefully, you will see the issue in the above photo. For those who don't know, the only thing that silicone sticks to is other silicone. The reason for the mold release is to provide a thin film which prevents the adhesion. Here, you can see there is no parting line of any kind. You can see a slight variation in color where I didn't quite have the mix ratio perfect.
 
Step 7a, find a big knife:
Yeah, I had no other way to salvage my 2-part mold other than a big knife. More specifically, I used an old block plane blade which was still sharpened to a shaving-sharp edge. The biggest issue with this is that instead of a nice, clean half-way-up parting line, I will have a jagged, uneven edge. Still better than re-pouring $50 worth of silicone.
 
Step 8, enjoy my handiwork:
Here it is separated in to the two parts. On the left is the "face" of the steering wheel. On the right is the finger-bump back side. The small holes are air holes made by drinking straws with modeling clay in them. You can see how they were placed in Step 7 above. There is also a larger hole for a funnel which is where I will be pouring the resin, eventually.

No comments:

Post a Comment