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Thursday, October 28, 2010

October ELB

Despite a crazy work load, I was able to get a lot done this month. The machining on the new AL hubcaps is complete. They're made out of 2024 alloy, which is very tough as aluminum alloys go. Check it out:

(Ignore the chuck changes...these images are from different days.)

The apparent warping is from the thick coat of oil covering the part.


Lathe work done
Sorry, fuzzy.

Scale: these are 3.25" in diameter.
24ish hours total spent in the machine shop. Polycarbonate plugs will be press-fit into the big holes to maintain waterproof-ness (remember, one of the goals is to have a waterproof board I can ride in the rain/snow). You can sorta see the ring I left inside the bearing pocket- that's for spacing out the bearing so the inner bearing race doesn't rub on the outer wall (learned that from the first set of hubcaps). The large holes in the inner side hubcaps (the ones that don't look like swiss cheese), are for the massive 2" bearings I bought. See previous posts for why I'm using 2" bearings. Anyways, they came out really great.

The next step is to figure out how to make the polycarbonate plugs. I bought some 1/4" and 1/2" PC rods and plan to cut them into 80 plugs. The big problem is figuring out how to polish the ends so that they are see-through. There are a number of ways to polish polycarbonate:

Potentially the best way is methylene chloride vapor polishing. This method basically eats the top surface (and thus the scratches) of the PC part, leaving a perfectly smooth (and thus clear) finish. The problem with this is that methylene chloride is nasty stuff, and I don't have access to a vent-hood. So that won't work for me.

Another method is dipping PC parts (or any clear plastic parts apparently) in certain types of floor was (like Future) and letting the wax dry on the part. Apparently, this results in a perfectly clear part (I guess the wax fills the scratches?). I know R/C plane hobbyists use this method to refinish their cockpits. My problem is that my motors will give off heat, possibly melting the wax. 

Another way is to just sand the ends with steadily finer and finer sand paper, and then use polish (like jewelers rouge) on a buffer. I tried this, but the ends were still very hazy. I'm going to try again with finer grit sandpaper (like, 800 if I can get it local).

Yet another way is to heat the surface of the PC part to the point where the surface melts. Unfortunately, you have to make sure you are evenly heating the surface, and only the surface. If you overheat parts of the PC, it'll bubble. I tried this method, too, with a heat gun, but the edge got a lot hotter than the center, causing bubbling. However, the parts that weren't bubbled were significantly clearer than the polished ones, so if I can figure out some other heat source, I'll try this method again. Results:

The outer two are sanded and polished (note haze). The middle one was heated (note bubbles).

Anyone have a good way to polish polycarbonate?

Here's a sneak peak:

Beginning the electronics layout.
Note the old hubcaps.


  1. Looks great, I really like the new hubcaps..should be a bit more durable than PC. ;)

    For polishing PC, personally I would go with the sanding method, just because that's what I have more experience with. If you want to get a really nice, clear surface though, you'll need to go a lot finer grit. Think of it kind of along the same lines as lapping a CPU (though I guess if you've never lapped a CPU the analogy is rather pointless :P ). Start with probably around 300-400 grit to get the surface flat (if it's not already), then gradually step up to 600, 800, 1000, 1500, 2000, 2500, etc, then take a polishing wheel to it. I wouldn't recommend jumping to a polishing wheel any sooner than 2000 grit. Once all that is done you should have a beautifully clear surface.

    Here's a good guide for what I'm talking about. It deals with plexi, not PC, but it should translate pretty well.

  2. OH MY GOD



  3. Wooooooow you have a lot of patience.