Bushing/Clicker Wheel

For several months I have been building an engraving mill and not producing any reels. So now I am back on reels, and have to re-familiarize myself with the processes. At the center of the reel is a critical part made of Delrin. It is the bushing for the spool, and it is one piece with the wheel of the clicker.
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I have been calling the toothed part a “ratchet”, but that may not be correct. Dictionaries say that a ratchet allows just one direction of rotation. A clicker has to allow bidirectional rotation, but the drag may be biased.
Although the teeth are cut with an “involute gear cutter” it is not really a gear either, since it does not mesh with anything.

I managed to scrap 3 parts before producing a useable bushing/clicker wheel. So here is a photo record to help me the next time I do this part.
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This is the simple fixture that I use, just a piece of shaft material drilled and tapped at one end, plus a clamp screw, washer, and spacer.

First I make a cylindrical blank that is .015 or .020 inch longer than the finished part.
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The fixed spindle for the reel is .250 inch diameter. I drill the blank with a .250 diameter drill.
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When a brittle material like metal is drilled, the hole is likely to be a little larger than the drill bit. But when drilling a tough material like Delrin, the hole is little smaller than the drill bit.
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So when I push the fixturing shaft into the new hole, it is a firm fit.

I next turn a .900 inch diameter (a little smaller than the gear dedendum circle) for a length of .97 inch, just .01 inch shorter than the shank of the finished part.
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So far, concentricity of diameters has not been critical.

But the gear OD has to be concentric with the bore. So I re-do the press of the part on the fixture, letting the shaft protrude from the toothed end.
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Then I center the fixturing shaft in a 4 jaw chuck.

The gear OD can then be turned concentric with the shaft.
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My 4 jaw chuck will mount to the mill’s rotary table, but the adapter may not bring it to center. So I check runout on the rotary table, and adjust the chuck as needed.
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The teeth can then be cut.
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The finished gear teeth are “fuzzy”, due to the toughness of the material.
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I can then remove the fixture and ream the bore.
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This reamer is 6.4 mm diameter, or .252 inch. Like a drilled hole, the reamed hole is a little smaller than the tool. It is a good running fit to a .250 diameter spindle.

At the toothed end, I then trim the part to final length.
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This removes some of the “fuzz” from the gear teeth.

In preparation for turning the shank diameter, I again center the mandrel (the fixturing shaft) in a 4 jaw chuck.
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Since reaming, the part slips easily over this mandrel.

At this point, I measure the bore of the mating spool.
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My spool drawing calls for a .4375 inch reamed bore, but the truth is that my Sherline lathe does not have enough low speed torque to make this. So I have to use a boring tool, somewhat less accurate. Also, the spool is anodized, which reduces its bore.

I turn the shank of the part so it has .001 to .002 inch interference with the spool bore.
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Here I am facing the other side of the gear teeth, removing the last .01 inch extra width.
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The recess can then be cut.
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This particular boring tool works well on Delrin when moved radially with the cross slide.

Finally, I give the gear teeth a haircut. This nipper is a “desprue” tool from Micromark.
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This entry was posted in Bushing, Ratchet/Gear, Thrust Bearing. Bookmark the permalink.

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