Mini-Lathe - torque upgrade

 Inspired by Ted Hansen's book, I resolved to increase the torque available at the chuck using a smaller motor pulley.

Ted provides all the details of how to make a new pulley in his book. However I reasoned that if I could learn how to specify a timing belt pulley, which would entail learning how to specify timing belts, I would probably be able to find a ready-made pulley that I could buy. The target pulley: 12 teeth, 8 mm bore, 10 mm wide.

The standard pulley has 17 teeth; moving to a 12 tooth pulley should give us a 28% torque increase.

I discovered that timing belts typically come in a variety of forms centred around the shape of the teeth. The lathe uses a belt which has a trapezoidal form, and this is called an AT format belt. The pitch of the teeth is 5 mm which makes it an AT5 belt and it's quite easy to find an AT5 format pulley with a 10 mm width. The difficult bit is that the hub is typically quite small - the one I found had a 10 mm diameter hub which I needed to bore to 8 mm, which therefore has no room in the hub for a grub screw: the screw had to be drilled and fitted between the teeth of the pulley.

With the new pulley in place, I spent some time adjusting the level of the motor such that the belt would run in the middle of the pulley. From the dust on the end of the motor it appeared that the original pulley had allowed the belt to rub against one end and slowly abrade the belt.

With the adjustments I made the belt now runs in the centre of the new pulley which should lead to less wear. 

You can notice the change in motor speed versus the spindle speed now that the gearing has changed but you will have to wait for the next instalment to hear if this has made a difference to the depth of cut that I can successfully achieve.