PM932 Mill Motor Upgrade

[Muskt]

Hello group. I haven't posted in quite a while; however, I read most of the posts here daily.

I have a PM932PDF mill that I am in the formative stages of getting ready to think about upgrading the motor to 3 phase with a VFD.
I figured the best place to start would be with the motor. Below is a pic of the data plate on the side of the existing motor.

I have unsuccessfully Googled the model number (and several variations of it) and have located nothing in English that I can use.

If anyone out there has any info about a 3 phase motor that will fit this mill, I would be grateful if you could pass it on to me.

I have not pestered Matt, yet. He will be the next source if no one on the forum has any info.

Thanks a bunch,
Jerry in Delaware

 

[markba633csi]

That looks to be about 1.5 Horsepower- do you need more power or variable speed?

Mark

 

[mksj]

Hi Jerry,

I had helped a few HM member's with their 932 VFD conversion from single to three phase. I believe the options on a 3 phase motor is to get one from Matt, but a possible alternate is 2HP LEESON 1800RPM D90LD IP55 3PH IEC MOTOR 192206.00. You would need to remove your current motor and measure it against the Leeson posted dimensions specific to the flange and shaft dimensions.
http://www.electricmotorwholesale.com/LEESON-192206/

There have been several postings on the conversion, this is one and you could PM the machine owner JayZ for details:
http://www.hobby-machinist.com/threads/pm-932pdf-3ph-vfd-conversion.47835/#post-408830

I have attached several older files and suggestions as to controls and parameters which if I recall was for a QMT replacement motor that was 1.5Hp, also some layout suggestions, this uses momentary (3 wire control) for the run/stop and rewires the stock direction switch for low voltage VFD direction. Just as a starting point as you need to be careful in the rewiring. I have additional information, but would need to do a lot more digging to find it.

JayZ did a very nice tach and controls install.

Install on another PM932, I do not recall the motor he used, but I could email him if you want me to check. In this install he uses 2 wire control so the direction switch directly operates the VFD inputs. In all these cases if I recall the stock power on contactor energizes the VFD, in alll cases the VFD is directly connected to the motor. There are some safety issues with using 2 wire controls so the spindle does not start when the VFD is powered up. There are various ways to address this with 2 wire control.

 

[Muskt]

Thank you both for the response. I am primarily interested in the speed control gained by the VFD.

The Leeson motor may be the ticket. The company (Electric Motor Wholesale) you mentioned, MKSJ, is where I purchased the 3 phase motor for my 12x36. They are only about 40 miles from my home, and although they are primarily a mail-order company, they were extremely helpful with my previous purchase. BTW, their prices were the best that I found during my search.

I will measure the existing motor, & then decide when/if to proceed.

Thank you again,
Jerry in Delaware

 

[TomS]

I thought about using a 3750 rpm motor to get some more speed out of my PM-932. Called Matt and asked his opinion and he said the gear head is not designed to operate at higher speeds. IIRC the gears are not hardened and higher speeds could cause premature failure. Might be worth a call to check this out. I asked my question about 2-1/2 years ago. Maybe they've made some changes to the gear head.

 

[Muskt]

My intentions are not so much for the increased RPM, as for the flexibility to find the sweet spot.
I have found that only a few RPM difference can make a considerable difference in overall finish quality.

Jerry in Delaware

 

[mksj]

With a 3750 RPM motor you would loose significant Hp at the lower speeds, and as Matt indicated the gear train is not designed for those speeds. My last mill was a gear head and went to 3000 RPM, was very loud and I worried about it's longevity at any sustained time at that speed. Also the spindle bearings would heat up to the point that it was almost too hot to touch, 2400 RPM was doable. My experience with mill/lathe motors driven with VFDs is that they perform much better using a lower speed motor and over speeding it. You have more poles for the same RPM which gives you both torque and smoothness. A good example of this recently was with a PM 949 that had a two speed constant Hp motor, we opted for the 4 pole (1750 RPM) and it performed very nicely on the lower speed setting and doubling the base speed 60 Hz to 120 Hz to get the same maximum speed. Since motors are constant Hp above the base speed, you would have twice the Hp at 120 Hz when you factor in the drive ratio relative to a 3750 RPM motor. I also agree with Jerry that it is very easy to dial in the sweet spot on the fly, although I find the lathe this is even a narrower RPM sweet spot. The other benefit of running the VFD in sensorless vector is absolute speed stability, usually maintains within a few RPM regardless of load.

Specific to the 932/940 VFD conversions, I have usually recommended not exceeding 75Hz for any continuous work. You may want to consider a synthetic/high quality gear head oil which both reduces drag and foaming at speed. I did this on my gearhead and differences were very noticeable. Usually in CNC conversions I see converting gear head mills to a two speed belt drive and using a 2Hp vector motor that can spin up to 6000 RPM.

 

[TomS]

"Specific to the 932/940 VFD conversions, I have usually recommended not exceeding 75Hz for any continuous work. You may want to consider a synthetic/high quality gear head oil which both reduces drag and foaming at speed. I did this on my gearhead and differences were very noticeable. Usually in CNC conversions I see converting gear head mills to a two speed belt drive and using a 2Hp vector motor that can spin up to 6000 RPM."

MKSJ - This is what I did, with your help. Works great.

 

[Muskt]

Today. I went out to the shop and removed the motor from the mill. I laid it on its side & did a bunch of measuring. Virtually everything is the same as the Leeson 192206.00 except for one thing, & that one is a show stopper. The factory motor has a 19mm shaft, & the Leeson is 24mm. Game Over!

So, I emailed Matt & asked if he has any 3 phase motors that fit. I told him that I was in no big hurry. I will post with his reply when it arrives.

Jerry in Delaware

 

[wrmiller]

I am not familiar with the 932 internally, but what fits on the motor shaft, a pulley or gear? Could you not bore the pulley or gear to accomodate the larger motor shaft?