Wednesday, October 01, 2008


Testing the envelope

Well, it's been about eighteen months since hitting a milestone on my Reprap work has caused me to to break out my 12 year-old Mcallans' single malt. Tonight... is the night, though. I should possibly have published this in the Builders' blog. I reasoned that you could do this with a Darwin, however, so I published it here in the main blog instead.

What you are looking at is a six-toothed involute profile sprocket gear cut on Tommelise 2.0. It has a pitch radius of 6 mm, a pressure angle of 20 degrees and with its involute profile surface defined by six planes. I cut it with a 1/16th inch cutter mounted in a flexible drive shaft on a standard Dremel hand tool mounted to Tommelise 2.0's positioning robot. It was cut in commercial 1/4th inch black, HDPE sheet. This sprocket is probably smaller than it needed to be.

I wanted, however, to test the envelopes of my Slice and Dice software, the cutter and the positioning accuracy of the Tommelise positioning robot. I could probably get eight teeth on a 6 mm pitch radius gear, but that would be right at the limits of my system.

It took me about two and one-half hours to cut it. Most of that time was spent worrying that I'd mar the piece. It should go quite a bit faster in future now that I have the parameters for working HDPE on this machine.

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