[Galane]

For the leadscrew drive on my lathe I have a 77mm center distance on the shafts with very little adjustment. If need be I can make an idler to push in on the belt, so it needs to be a type that tolerates bending backwards.

I want to do a 2:1 reduction from motor to screw. The motor has a 3/8" shaft while the screw has a 10mm shaft. Oh the joys of surplus components! I can put one pulley in a lathe and ream it out to 10mm.

Right now the rest of the specs for the motor and screw don't matter, Linux CNC can take care of how far each 1/2 step moves the lathe carriage. I just need a cogged belt and matching pulleys that will provide the 2:1 ratio and fit the center distance. Metric, Imperial, tooth profile, doesn't matter. Any of the available types should be more than strong enough to handle driving a carriage leadscrew on a 9x20 conversion.

If you really must know, the motor says 450oz holding torque, 200 steps. The leadscrew is a 16 mm per turn linear actuator enclosed ball screw. Happened to be exactly the right length to bolt onto the front of the 9x20 bed and I milled an aluminum motor plate which bolts to both the drive end of the actuator and the headstock end of the bed. The drive system isn't going to shift any which way.

So driving the motor 1/2 step = 400 per revolution. 2:1 ratio = 800 1/2 steps to turn the screw once. Thus 16/800 = 0.02 mm linear motion per motor 1/2 step. The Slo-Syn part number data sheet says 5% accuracy so trying for 1/16th stepping to get 0.01 mm movements is likely an exercise in impossibility with this motor. Not going to be building an interferometer or atomic force microscope with the lathe...

[RCaffin]

Metric, Imperial, tooth profile, doesn't matter. Any of the available types should be more than strong enough to handle driving a carriage leadscrew on a 9x20 conversion.

Strong enough, yes, but the older imperial belts such as Xl give a bit of backlash.
Modern designs such as GT2 or GT3 are essentailly backlash-free. They are stronger than the old designs too.
You will find belt calculators on various websites.

16mm/turn is very coarse for a leadscrew. 5 mm/turn would be more realistic.

Cheers
Roger

[louieatienza]

sdp-si.com.... they even have a belt calculator. As Roger says, get GT3. Most ballscrews have metric shafts, leads, etc.

Most every stepper motor has a step accuracy of +/-5%. You'll increase your chances of better resolution by using a larger reduction, and you'll still have good speed with the high lead screw.

[Galane]

I did some digging around and found I have a 13XL and a 22XL pulley. The 22XL already has a 3/8" bore that will go right onto the motor. I can use the 13XL as an adjuster idler and only have to buy a 44XL pulley and a XL belt with at least 64 teeth.

As I said, not intending to do exxxxstreeeem precision stuff with the lathe formerly known as a JET 9x20 which only cost me $50. Low cost building is the goal. I shopped closeouts and clearance sales to get all new, name brand bearings and belts when I rebuilt the vari-speed drive on my knee mill. Total cost under $100 for the parts. (Don't ask about having to make new sliding sheave bushings from scratch due to that industry abandoning keyed shafts on 3HP drives.)

[RCaffin]

Well, if you have them ... But seriously look at GT2/3. You can get a fair bit of GT2 6 mm stuff very cheaply on eBay - bulk buys for the RepRap market. You might be surprised at just how much power you can put through a tiny 6 mm GT2 belt - I was. it worked very well.

> closeouts and clearance sales to get all new, name brand bearings and belts
Except that sometimes you find that what they are selling are actually cheap Chinese clones which don't always fit properly.

I bought what was advertised as 'Polyflex 5M710' belts for my lathe from West Coast Resale via eBay, but they turned out to be over-size Chinese copies which do not fit properly. They are too wide and the clutch action on the headstock does not work. Polyflex is a registered trademark of Gates Corp; these belts are unbranded. I have enailed WCR and filed a refund claim, but so far I have not heard anything back. UNHAPPY.

Cheers
Roger

[Galane]

Got the 44XL pulley for $7.20, free shipping, and with 10mm bore I won't have to change that. https://jet.com/product/508mm-Pitch-...2c9b97fc597fe8

Now to find a suitable belt of 64 or more teeth. That site doesn't have the belts even though they have many different XL pulleys.