The integrated bearing holders pushed the maximum overhang capabilities of the support material-less MakerBot pretty hard, but they printed just fine.
The whole center wheel part was printed in 1 hours and 26 minutes. I slowed down the feed rate of the printer to 20 mm/s, since there are quite filligree parts to print at a 45° overhang. So I want to print this thing nice and slowly.
Of course, the raw part needed some cleanup after printing. But I guess that’s ok. After all, it’s a pretty sofisticated shape to print…
I put together a 6 or 7 minute video on the assembly where I show all involved steps to clean up and assemble the final wheel:
I printed the half roller parts in two batches. I used Skeinforge’s “Multiply” tool to generate 3×3 rollers. I also used the “Tower” tool with a moderate setting of 2 layers per turn. Printing one batch of 9 half rollers took about 1 hour and 10 minutes, so the total printing time for all printed parts of one complete Mecanum wheel (plus two spare roller parts) took about 3 hours and 45 minutes. That was much less than I thought.
When assembling the wheel, I used two washers on each side of the ball bearing. I have the feeling, that the additional distance makes the rollers more reliable. I used two different sizes of M4 washers, the larger size (OD 12mm) are a almost perfect fit for the printed rollers. I bought them by accident (wrong size) for my Mendel build, so I have a lot of them. However, they are to large for use directly next to a 624 ball bearing. So I used the normal sized M4 washers (OD 9mm) for direct contact to the ball bearing.
Inserting the M3 nut in the center hole and mainly inserting a M3 set screw is quite a fiddly thing, but not as bad as I suspected. It should also be possible to use a normal M3x15 bolt instead of the M3x3 set screw I used. Your mileage may vary.
Ok, that’s that. The STL files are published at thingiverse.com: http://www.thingiverse.com/thing:2473
Now, I need 3 more of these and a base plate to continue with my open source robot vacuum project…