Another Mill Choice Dilemma

[ptrotter]

Reviewing the information, it probably comes down to how much travel and drive system speed you need and less so about Chinese vs. Taiwan. Another factor would be available kits if you do not plan (or have the ability) to mill the parts to convert to CNC. I would probably go with the PM-940V-BASICw/HRDWYS, it is basically setup for conversion to CNC, it is a 2 speed Low 100-1640 RPM, High 350-5000 RPM variable speed head. Probably beyond 5000-6000 RPM the bearing would need to be switched out and change the pulley ratios. It has an option for hardened beds, you would want to add an automatic oiler. Seems to be a number of CNC kits available, this was also can include Clear Path or DMM servos. I had looked into DMM servos in the past and they have some very nice drives/controllers. If going with the PM-833, the TV seems to be a more logical choice for reliability and convert the head to a 2 speed pulley belt system. In both mills you are already starting out with a VFD rated motor and drive, the downside would be if there is any provision for interfacing its control with a CNC system. You could interface a control relay to turn on/off the drive. You also could check if any of the CNC retrofit vendors have something in the works for the PM-833TV. Both mills are close to the same price, but for a CNC conversion project I think the PM-940V has a bit more going for it.

PM 940M CNC conversion Kits

Mark,

Somehow I seemed to miss the 940V completely. I swear it wasn't on their website this morning. This looks like it could be a good option. I was leaning toward the 940M but didn't like the gearbox so I was thinking the 833TV but this changes things. I'm not sure how they do the variable speed on the 940V though. The specs say it is a single phase motor but that could be a misprint held over from the 940M specs. Hopefully it is actually a 3 phase motor. If the column and the bed is the same as the 940M, the ArizonaCNCKit conversion would work. I'll call PM in the morning and find out more. ArizonaCNCKits is suppoedly coming out with a belt drive conversion for the 940M as well but he hasn't started on it yet. I believe it will be a 2 speed unit which would be great. I already have a sherline mill set up for CNC with a Centroid Acorn board so all I would need to do is put in the appropriate stepper or server motors and bigger motor drivers and I will be set. The electronics are the easy part for me. I know nothing about ball screws and nuts so that is why I am looking for that as a kit.

Paul

 

[davidpbest]

Yea, I referenced James’ spindle in the other thread. If the conversion is essentially eliminating everything except the castings, then the insistence on Taiwanese-made seems to me to be largely irreverent.

 

[ptrotter]

I’d be interested in a stripped down PM Taiwan bench top mill for CNC conversion. No motor, ball screws installed, no motor, axis and motor mount options.


Check out Clough42 spindle upgrade for his Grizzly. Very impressive what a $3000 12k spindle can do on a benchtop mill. That video series, actually the test cuts, really made me want a CNC.


Sent from my iPhone using Tapatalk

The Clough42 videos are great. I think I have watched all of them, including his ATC spindle conversion. His videos are what prompted me to get moving on getting a mill.

 

[ptrotter]

You get a 3 year warranty, it either holds up or fails. If you want a higher speed spindle or worried about longevity there are better bearings. If the motor eventually fails, then replace it with vector motor, and if you want power tapping add an encoder. I worked with a number of individuals that went with the PM-932 in the past (before a 940 was available) and they added a Marathon Black Max 3 Hp motor. More recently there have been some AB (same as Baldor) vector motors that one person went with a 3 Hp in his mill and another a 5 Hp 130lb brute in his lathe.

Mark,

Do you know how the person who put the Black Max motor on the PM-932 dealt with the shaft size differences? I assume the PM uses metric shaft motors, but maybe I am wring.

Paul

 

[davidpbest]

Mark,

Somehow I seemed to miss the 940V completely. I swear it wasn't on their website this morning. This looks like it could be a good option. I was leaning toward the 940M but didn't like the gearbox so I was thinking the 833TV but this changes things. I'm not sure how they do the variable speed on the 940V though. The specs say it is a single phase motor but that could be a misprint held over from the 940M specs. Hopefully it is actually a 3 phase motor.

The 940V didn’t hit my radar screen until early this afternoon. I will be interested to hear what you find out from PM. You’d think that when they introduce a new product, they’d blast out a post or email with more details.

My bet is that the machine has a two-speed, 3-phase motor, and the electronic controls switch the VFD output between the different windings to achieve low and high speed. My RF45 (sold when I got my PM935) had a two-speed, 3-phase motor, and even without a VFD would operate the spindle at 3,100 RPM. Assuming the motor is of sufficient quality, it’s easy to see how 5K is within reach with the VFD putting out ~100Hz.

My questions are more about what’s been done to the gear train and spindle bearings to actually handle 5k RPM on a consistent basis - especially since this is from China and not Taiwan. One thing is for sure - it going to be loud.

Please let us know what you find out.

 

[ptrotter]

The 940V didn’t hit my radar screen until early this afternoon. I will be interested to hear what you find out from PM. You’d think that when they introduce a new product, they’d blast out a post or email with more details.

My bet is that the machine has a two-speed, 3-phase motor, and the electronic controls switch the VFD output between the different windings to achieve low and high speed. My RF45 (sold when I got my PM935) had a two-speed, 3-phase motor, and even without a VFD would operate the spindle at 3,100 RPM. Assuming the motor is of sufficient quality, it’s easy to see how 5K is within reach with the VFD putting out ~100Hz.

My questions are more about what’s been done to the gear train and spindle bearings to actually handle 5k RPM on a consistent basis - especially since this is from China and not Taiwan. One thing is for sure - it going to be loud.

Please let us know what you find out.

David, I'll see what I can find out. Looking at the picture closer, it has a 2 speed belt drive and the motor looks like a 3 phase motor. If so, I think it would be a great choice , it pretty much matches what I had described in my initial post as ideal for me. I would probably replace the VFD and the control panel to match my needs but that is not a big deal.

Paul

 

[addertooth]

I would toss in that the brushless motors are inherently 3 phase. Which is why with their small HP figures they have rather good torque.
They have the bonus of not needing your shop wired for 3 phase power. An example would be the PM 728VT, which has a peak RPM of 4000 as well. It is a two speed belt drive. So it is quieter than many of the gear-drive bretheren.

 

[davidpbest]

David, I'll see what I can find out. Looking at the picture closer, it has a 2 speed belt drive and the motor looks like a 3 phase motor. If so, I think it would be a great choice , it pretty much matches what I had described in my initial post as ideal for me. I would probably replace the VFD and the control panel to match my needs but that is not a big deal.

Paul

Bingo! I see it now. Kipp lever to release belt tension, handle to swing the motor, clear markings on the face of the head. Ugh - not what I was hoping for or how I would have spec’d it. Worse than the backgear on a J-head. Fine for manual mill I guess, but you aren’t going to find any G-code that will change that belt position from a CNC controller. Too bad they didn’t put this two-belt position setup on the 833TV - that would have resolved my issue about low end torque on that model.

My thinking is still more in the camp of using the ATC spindle James is putting on his Grizzly mill - or something similar. That seems like a viable alternative to using the OEM spindle and upgrading bearings, Black Max motor replacement and a PDB and still stuck with R8. But I’ve been back and forth more than a dozen times.

 

[ptrotter]

Bingo! I see it now. Kipp lever to release belt tension, handle to swing the motor, clear markings on the face of the head. Ugh - not what I was hoping for or how I would have spec’d it. Worse than the backgear on a J-head. Fine for manual mill I guess, but you aren’t going to find any G-code that will change that belt position from a CNC controller. Too bad they didn’t put this two-belt position setup on the 833TV - that would have resolved my issue about low end torque on that model.

My thinking is still more in the camp of using the ATC spindle James is putting on his Grizzly mill - or something similar. That seems like a viable alternative to using the OEM spindle and upgrading bearings, Black Max motor replacement and a PDB and still stuck with R8. But I’ve been back and forth more than a dozen times.

Maybe not optimal, but then how often do you have to change the speed enough on a single setup that you would need to change the speed range. Still better than a gear box. At least it should be reasonably quiet. Why would you have liked this on the 833TV but not on the 940 except that the 833 is Taiwanese?

For my use case this is probably a good alternative. Large work envelope, good speed, and decent low speed power with minimal upgrades required. Assuming the castings are the same as the 940M, the CNC upgrade using the ArizonaCNCKit conversion is fairly simple. Perhaps a future motor upgrade and new VFD, but that would not be necessary anytime in the near term.

I wonder what kind of low speed torque you get with the ATC spindle that James is using? I do like the ease of tool change though.

Thanks for your comments. your insight is appreciated.

Paul

 

[mksj]

I do not know the specifics as to the PM-940V, but I would assume it is akin the the PM-833TV vs. the M. Belt drive, and in the PM-940V it has a more desirable 2 speed belt drive. It is purposely built for CNC conversion, I see no reason for QMT to add more customization when there are other individuals already offering decent conversions. Often individuals want different build specs. such as the ball screws, so better to allow people to outsource these components then try to carry all the options. Give QMT a call and you should be able to get more details.

So an old thread on a full CNC conversion of the PM-932, I think a lot of it was based off of conversion that JBOLT did. In most of these builds the old gear box is removed and a belt drive is implemented. I can't recall if JBOLT also went with a Marathon motor. TomS pretty much milled all new hardware for a 2 speed belt drive. Since the vast majority of CNC involved small cutters, I think the need to change the belts speed would be infrequent. Even when I run face mills, in steel for a 2.5" I run 600-1000 RPM, aluminum 2-3X that speed. Shouldering in steel, still in the 600-800 RPM range. Inverter/Vector motors have full torque almost to 0 RPM and you can easily dial up the VFD's to 180-200% overload for up to a minute. Given that they top out at 6000 RPM it gives a very wide operating window. Some industry people will even push the vector motors 10-20% over the max RPM w/o issue, but I see no practical reason to do so in this application. If one wants to be in the 8-12K spindle speed region, then going with a more purposely built CNC mill like the Tormach 1100MX will take you to 10K RPM. The pricing on the 3 HP ATC ISO spindles I saw listed was pushing 3K and then one needs to adapt it to your mill head, there are some Chinese variants for less, and back to long term reliability.

Taking the CNC Plunge

you jumper them at the plug just like X and Y, they will fit in the connector housing. Steve

www.hobby-machinist.com

The PM-940V is single phase input, i.e. but the variable speed motor is not single phase. I am assuming that the motor is an inverter style, it may be a TEBC from the pictures, which is what I have on my mill. These typically operate from 15-20Hz to 200 Hz, so a much wider usable speed range. The approach one would take depends on the the end point of the conversion and how deep your pockets are. One can take as basic approach, that the drive system is at least good to 5000 RPM, and longevity wise should last a long time. At least as a starting point. Arizona CNC seems like they will put together all the parts, and do some customization as to drive components. Their pricing seems very reasonable and they offer different build levels as to the drives selected, and in some cases priced below market pricing. Also may provide post sales support.