Sunday, May 6, 2012

Router lathe: motor mounts and drive mechanism

Here's the feed motor mount and feed screw. The stepper motors are the yellow blocks. The screw is stock 1/2"-13 threaded rod. I picked up a flex coupler at a local surplus store, and put adapters on each end to convert from 1/4" at the motor to 1/2" at the feed screw. the black bearing material the rod runs through is UHMW. It was tough finding a piece of rod that was straight enough. Measuring over 42", the pitch is at least a half thread off (I didn't count, so it could be more than that). My intention is to replace it with 2-start 1/2" acme threaded rod, once the mechanics are all figured out.
 Tailstock end of the feed screw using same UHMW bearing.

Spindle drive. My auto mechanic gave me a selection of discarded timing belts. This one's from a Honda, I think. They are huge, but work great. I figured out what the gear circle would be for a 60t gear and drilled holes in a piece of particle board using a rotary table. Then cut & sanded the corners off till it fit. The particle board was just a test, but it works so well, I'll keep using it for now. The black adapter attaching the gear is acetyl turned to fit the spindle.

Spindle motor mount. The small gear is UHMW. This was cut the same as the particle board gear -- close guess on diameter, drilled holes and cut the diameter -- x-acto knife to round the corners. Not terribly pretty, but it runs well with very little backlash or slop. I plan to replace all these "Land of the Giants" parts with much smaller .2" pitch XL belts and pulleys, but this gave me a way to test whether a 4:1 ratio was good without buying a bunch of parts. There's a 5/16" shaft through the small gear and skateboard bearings pressed into the pulley housing, and one end is turned down to 1/4" so a simple coupler could be used to connect it to the motor shaft. This allows the belt to be tight without putting lateral stress on the motor.

(the 5/16" coupler was loose, causing inaccuracies in the first part cut. I thought there was a problem with electronics or code, but so far, all my major mistakes have been mechanical)

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