Lovejoy Coupling For Lathe

[Muskt]

I just came in from the shop where I had been sitting and thinking (Yeah, I know--I'm in trouble now.)

I am considering re-powering my lathe with 3-Phase & VFD. OK, what's to think about? Well, I'm still getting a bit of vibration--not lots, just "some vibration".

Soooo, here is the question I came up with. How about fabricating some type of mount off of the left end of the
lathe and using a Lovejoy coupling for direct drive (not to the spindle!!!) and eliminate the belts & pulleys?

The mount could be attached to the base that I have already constructed and the current motor mount would serve as an outrigger to keep everything steady.

Since I have never seen or even heard of this type of mod, it is probably not practical. Just some random
thoughts (no alcohol was involved).

Jerry in Delaware

 

[tmarks11]

Well one reason why not is that generally the belt provides a speed reduction of 2.5:1 (at least on my lathe). Going direct drive is going to make your lowest speed 2.5x as fast.

Yes, you can slow down the VFD, but you are losing torque in the process.

Another reason is that the belt provides some vibration dampening, especially if you use sound mounts to mount the motor. Love-joy coupling might not work as well.

 

[Ulma Doctor]

when are you experiencing the vibration?
is the vibration consistent between materials?
is the motor in serviceable or worn condition?

 

[Muskt]

Thanks for the replies.

I was aware of the speed change--that is important, especially considering that the stock motor on the lathe is something like 1400 RPM (really don't remember).

The vibration occurred badly on the low speed pulleys with the Chinlee belts. Replaced them both with Gates and not a significant change. Removed one belt & a bit better. Moved the single belt to the high speed setting and much better--although not as good as I would like.
The machine is a PM 12x36 with maybe 10 hours on it.

I am pretty sure the problem is not the motor. With no belts on it, there is no vibration. With one on the high speed range, it is very small. I cannot observe any wobble on the motor pulley or the lathe pulley; but that is not a definitive observation. It would not take much to create the vibration I am observing now.
The vibration manifested itself first with the shaking of the work light--I could feel it, also. Now, it is nearly non-existent. The finish on all metals showed vibration, also. Not the Barber Pole lines like chatter, more like a slightly "hammered" finish--actually pretty hard to describe.

As to my original question about the Lovejoy, I was mostly just thinking out loud and wondered if anyone had ever done anything like that. I have (in a past life re-powered a small lathe with a real DC motor & drive--fabbed my own mount to make it fit.

Anyway, again, I am not terribly concerned about the vibration, yet. I am still attempting to get the shop set up and just having a great time doing it. If, and when, I do get around to it, I'll contact Matt & seek his wisdom.

Thanks for listening.

Jerry in Delaware

 

[mksj]

I would review this thread, that had the same issue and was corrected by changing the belt tension of the linked belt. There have been a number of discussions on this issue, some lengthy specific to the PM1236 and G4003G. Sometimes resolved, other times not. Linked belts work for some, but others it does not. If you do not use a notched or cogged type belt, the standard belts tend to get a set when around the smaller pulley, this can also cause vibration.
http://www.hobby-machinist.com/threads/lathe-barber-shop-pole-pattern-loose-carraige.36912/

Try a different belt, such as the Gates tri power:
http://www.gates.com/products/autom...d-accessory-belt-drive-system/tri-power-belts
http://www.royalsupply.com/store/pc/BX-Tri-Power-Belts-c1095.htm

There have also been issues with the pulley wobble (bored incorrectly) and misalignment of the belt(s), belts not matching (dual belts), pulley alignment sometime requiring redrilling the motor mount to get the pulleys to align. Others have discussed isolating the motor with rubber dampeners available from McMasters, and/or issues with the Chinese motors. Could be poor motor balance or bad bearings, check the motor vibration with no belt on. I am assuming the spindle bearings are fine in a new machine. So would check alignment, try to adjust the belt tension and/or try a different belt. least expensive and easiest fixes. The other major factor is just the cogging from the single phase motor, moving to a 3 phase motor would significantly even out the power delivery to the machine and decrease vibration. VFD adds flexibility and features in this application. FYI, in sensorless vector mode torque is usually the same at lower speeds, but HP drops off in a linear fashion below the base speed at 60Hz. Direct coupling would not work well unless you up sized the motor to compensate for the pulley ratio loss, let alone how it would be installed. I would try to address the issue with more conventional fixes that have worked for others.