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Unimat 3 drive questions

Drive belts and pulleys

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John Sykes 120/11/2021 12:24:28
10 forum posts
1 photos

I'm currently adapting the lathe to run from a variable-speed brushless spindle motor. This runs to a maximum of 10,000 rpm and the stated torque is 0.5Nm.

I have a couple of choices of drive belts; so called "Y" section cogged V-belt (6mm top width) or one of the smaller HTD toothed belts.

I'm concious that the lathe is relatively delicate, and that the O-ring drive probably slips under excess load and protects against potential damage? Does this suggest that a small v-belt would be preferable to a toothed belt? Are the latter noisy?

I'd also be interested to hear from any Unimat owners as to the principle speed range(s) which cover a majority of work, I can probably use a 2.5 to 1 reduction which would then replicate the name-plate maximum speed of 4,000 rpm, but the lathe currently seems to run faster by some margin under no load.

Will 1Nm+ torque be sufficient for most turning work?

Many thanks


John Haine20/11/2021 13:28:00
4631 forum posts
273 photos

I use standard "Roundthane" belts which use a little barbed joiner. No sign of slipping.


John Olsen20/11/2021 20:39:21
1240 forum posts
94 photos
1 articles

In standard form all of the no load speeds are considerably faster than the name plate rating. If I recall correctly, the ratios between them are also incorrect, the lower speeds being higher again than they should be. This doesn't matter too much, unless you set up to do screw cutting, in which case a handle in the spindles is a better bet than using the motor.

I converted mine to use toothed belts about 30 years back, the little ones about 3/8 wide. I think this was published in MEW some years back, although I don't have a copy of that. I can dig out the files if needed. The setup I used fits inside the original belt cover. A later change was to put a countershaft where the motor would normally be, and provide two steps on the pulleys there. Those ones use a poly V belt. The motor I am using with it now is a 1/8 horsepower three phase one with a vfd, so now I have 8 steps of ratio change plus the vfd range of speeds. so I can go from really slow on up to about the original maximum.

The toothed belts will break if things get too hectic, so I have had no problems on that score. It does need a spare kept on hand just in case.

The current setup does not suit the milling attachment, so I have another motor mounting plate cut out and a DC speed controlled motor waiting to be mounted on it. Since I have a much larger 45 size mill drill, this has not been treated with much urgency.


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