On Jul 2, 10:44*pm, "Michael Koblic" wrote:
...
The two questions that bother me about the concept of a countershaft a

1) Is the 3M belt big enough withstand the torque at the lowest speeds? Or
would one have to go to a completely different transmission for the final
step (countershaft 2 to spindle), e.g. timing pulleys and belt?
2) If one were to make a pulley, how critical are the groove dimensions? The
only pulley I made was the wooden one (and it works just fine) but the
process can hardly be repeated with aluminium (or can it?)

Michael Koblic
Campbell River, BC

I usually set the belt on my larger lathe to slip with nearly maximum
hand pressure, on the little one to slip fairly easily. The leather
belt changes length with humidity so I have to readjust it anyway. The
motor and countershaft are on a swinging frame with a tension
adjustment screw in series with a toggle linkage.

Here's an adjustable cam tensioner that's easy to make:
http://picasaweb.google.com/KB1DAL/H...33137678036386
The bolt through the disk is 0.05" off center to pull or release the
forged eyebolt in the slot. You could put it 1/4" off for a 1/2" throw
to tighten or move the belt. Rotate the handle for fine adjustment,
flip it to quickly tighten or loosen it.

Machinery's Handbook 23 gives the following groove geometry for a 4L
vee belt:
OD Angle Width
2.65 30 0.485
2.65 - 3.24 32 0.490
3.25 - 5.65 34 0.494
5.65 38 0.504

We discussed this here once, IIRC some posters used 35 degrees and
0.5" width for all diameters. You could try it and change the groove
angle if the belt appears to be wearing quickly, but I suspect you
can't drive a Taig hard enough to harm a belt. The heavily loaded pump
drive vee belt on my tractor ran for 3 years and still looked OK when
it failed with a broken cord. It ran on home-made pulleys.

jsw