August 27, 2015

Mini Lathe Pulleys

I'm back from the left coast, and for once I'm not busy building giant wooden contraptions for orientation.  Instead I'm trying to finish the tiny lathe before classes start.

I made some 2L sized v belt pulleys for the motor and spindle.  I considered using timing belts, but the spindle's going to be pretty high speed (>7k rpm max) and figured v belts would be a bit quieter.  Not to mention, v belt pulleys are much easier to machine.

The pulleys were cut turned using a grooving tool ground from a HSS blank:

For the motor pulley, I had a lot of trouble getting a clean 9mm bore using the MITERS small boring bars, so I tried a technique seen here for making reamers.  I turned some 9.5mm semi-hardened steel shaft down to just under 9mm, and ground three facets in the end.  The faces were cleaned up on a whetstone, to debur the corners and get a sharp edge.  I drilled a slightly undersized hole, and expanded it to final diameter with the reamer.  The results was a pulley with a nice 8.99mm bore, which I tapped onto the motor shaft with a hammer.

Both pulleys are retained by set screws.  Normally I greatly prefer split collar style clamps to retain round things, but in this case it was hard to beat the compactness of set screws.  And it's dealing with fairly minimal torque compared to most things I build.  On the spindle side, the shaft diameter is fairly huge, which makes the force on the set screw smaller, and on the motor side, the pulley's press fit should deal with most of the torque.

On both the motor shaft and spindle I milled a little recess for the set screw to sit in:

Also notice the pair of lock rings for preloading the spindle bearings

And here's the spindle and motor pair:

Next up: Building a tiny quick change tool post.