Vfd & Pulley Questions - 12" Lathe

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Kilroy486

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I've had a Craftsman 12" cabinet style lathe in storage now for a little over a year now. I have a newer three phase motor & Teco vfd for it. I'm giving it a new home in the basement, and in the process broke her down to get it moved.
I'm about to replace the two original (they say Clausing on them) drive belts with link belts, as I don't want to tear down the headstock. And I got to thinking, since I'm going the vfd route - couldn't I just dispense with the whole mess of pulleys in (and outside) the cabinet & put two belts directly to the motor now?
Additionally, it looks dang tight in there to run the link belts through the opening in the chip pan down into the cabinet. They seem to ride a little high in pulleys as it is - anyone have problems with those in the cabinet style lathes?
Thoughts? I'm sure somebody else has already done the "heavy lifting" in this area.
Thanks guys!
 
A VFD can cover a range of speed, but you are looking at a something like a 4 fold operating range unless you increase the motor Hp and use an inverter/vector motor that can operate over a broader RPM range. Most factory VFD lathes in this size will cover about a 10 fold operating speed range with a 2 speed transmission, so something like 40-400 RPM, and 200-2000 RPM. So you would be better off retaining the current speeds and adding the VFD to give you an operating window of say 30-90Hz. Otherwise you would loose too much torque/Hp.

On the pulley and belts, it could be the wrong belt size vs. pulley size. Specifications should be online as to the pulley width and belt width dimensions. Replacement motor pulley will run about $25, and you may want to look at the ratios to optimize the speed for use with a VFD. I just did this on a cabinet style motor lathe and on mine.
 
you'll need the different speeds provided by the stepped pulleys.
if the motor is not rated for inverter duty you'd do best to operate it from 30 to 90 Hz under normal conditions.
the motor may overheat if operated for too long under out of it's operating envelope.
non-inverter duty motors can be operated at lower or higher frequencies for short periods of time without major problems.
link belts are great, but they don't transmit power well in the reverse direction
 
Installed the Fenner Powertwist belts - plenty of room. Went with 43", but they seemed too tight so I added an additional link for each belt. I like the fact that you can make a little adjustment for the double pulley in the cabinet to dial in the belt tension.
 
Link belts were originally designed for emergency repairs with minimum down-time of critical machinery. One of their primary benefits to commercial users was that they could significantly offset spare parts stockage costs. But they were not intended for continuous use. Their only other advantage over normal V-belts is that they don't require pulling the spindle to install them on an Atlas lathe. They have lower torque ratings, are more prone to slippage, and will wear out pulleys more quickly than a proper V-belt. And they have a higher initial stretch. In a few months, you will probably find that you need to remove a link from each. Plus (not usually a problem with Atlas lathes or mills) they are not reversible. The original belts were A42's. Properly installed, they are good for at least 35 years of intermittent operation (and counting). Link belts have no advantage over V-belts in the other two locations. They just cost more.
 
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