VFD or stick with single phase

[William C Rogers]

I have a PM 90 lathe. I have decided to raise the lathe up 3" giving me a 18" swing. I am pretty confident that I can accomplish that. I have all the materials in except for the new tool rest from Robust that are on order. when I got the lathe I changed to motor out to a 1hp 1725 rpm single phase. My speed range is 330-2100 rpm. With the 12" swing the 1 hp has been fine. 330 rpm seems ok for the low speed. Since I am going to a 18" swing,
is 1 hp ok? Should I just wait and see?

2 hp single phase motor is about $300 new.
VFD and new motor is about $400-$450 new.

looking for the lowest cost solution that works, is it worth the extra $150 for VFD? Benefit seems to be lower speed and reverse. Are they worth it? If I go this way should I get a 1800 rpm motor for a little higher rpm?

concerns I have with VFD is they say to keep away from dust. Do I need a special enclosure?

What at do you recommend?

[Guy Belleman]

Lots of lathes out there that you could refurbish from the start. Have you thought about selling the pm90 and start fresh?

[Larry Copas]

I did a similar conversion on a Rockwell 12” lathe about 9 months ago. I think it well worth the effort/money. The lower speed helps with out of balance bowl blanks and I also like the slow speed for power sanding. Sometimes I really go slow and sand by hand with the grain.

A couple of thoughts for your consideration. Used 3 phase motors can be found cheap, like $50 and less in that size range. With a 1 ½ HP motor you may be able to power it from a 120 volt circuit. 2 HP would normally require a 240 volt circuit. I used an 1,140 rpm motor because it was on hand and also gives me a bit more torque at low speeds. I'm using a cheaper Teco FM-50 VFD without sensorless vector control. Using a higher priced Vfd with sensorless vector control will not loose as much torque at slow speed. An 1840 rpm motor would work fine.

The Teco FM-50 line of VFD's have been trouble free for my use. I got my first one about four years ago and added a second one a couple of years ago. The one for the Rockwell is my third.

I mounted the VFD above and behind the headstock. Has plenty of ventilation, I can see the readouts, and I used the VFD keypad to adjust speed/direction. I soon tired of that location for adjustments so I added a remote pot and on/off/reverse switch. I shopped eBay for a quality AB pot instead of the cheap import junk.

I recently brought home a General 26020 with factory VFD and 2 HP. Other than swing and weight I see no difference in turning between it and my home built conversion.

[William C Rogers]

Thanks Larry, the Teco FM 50 is what I would use. I have looked for used motors, but not that much cost difference for me to buy new. Yes, I am concerned about dust and ventilation for the VFD. You didn't mention reverse. Do you use that?

Guy, not sure what you are suggesting. I have had this lathe for 6 years and know about it. Why would I want to sell and buy another lathe to refurbish? I have searched CL for about two years and have not seen any lathe I would buy that would be better.

[Larry Copas]

I do use reverse for sanding mostly. When I first installed my on/off/reverse switch I was concerned that I might accidentally go from wide open forward to wide open reverse and unscrew a chuck holding my work. I found out I didn't need to worry. The way my Teco FM-50 is programed the motor will slowly decelerate to a complete stop and than slowly accelerate to speed in the opposite direction. Of course the acceleration and deceleration speed is programmable in my VFD. It may not be programmable in other VFD's and a chuck could unscrew. Best to proceed with caution or lock the chuck on the spindle.

[Olaf Vogel]

William,
If you are looking to Increase your capacity, then a motor upgrade is great. VFD is a must IMO.

there are tons vfds on eBay, used, from China. Delta is a brand I've used on 3 machines (lathe, blower, bandsaw) without issues. These are cheap and shipping is often free. Check the specs, but most will covert from single phase. The manuals are on the web for download. Many of the domestic brands make it really tough to get clear info and are total pain to work with.

as mentioned above, used 3 ph motors are dirt cheap and almost indestructible.
I just picked up a 1 hp gear motor for $50. The most I've ever paid was $300 for 5 hp, 880 rpm monster.

Lower rpm motors are helpful, but harder to find.

Once you start working with vfds, you'll look back and wonder how you ever did without.
speed adjust, soft start, reverse...