Possibly upgrading a motor on a mill, what do I need to know?

[WobblyHand]

I have a PM25 mill. The 1HP motor doesn't seem to have good enough speed regulation at lower RPM. Where I see this is when using a slitting saw. There's not enough torque at low RPM's like 100-150 to not bog down in steel. The blade jams a bit, slows down, then overspeeds. It makes slitting a royal pain with a HSS saw. Is it possible to upgrade the motor? What would be involved? (New motor, new controller, new tach?) Is it possible to just do a pulley swap to gain a little extra torque? (Motor spins faster, but spindle is slower.) Exploring my options at this point.

Don't mind the envelope of the mill, although it could be larger. 95% of the time it is fine, especially considering the low ceiling I have.

 

[markba633csi]

You're not cutting dry are you? 1HP is a fair amount of power- I'm wondering if the controller current limit is mis-adjusted?
-Mark

 

[rabler]

Blondihacks (on YouTube) has a very similar mill. I think she does some work on her mill at various points, might not be exactly what you're after but may be useful for ideas.

 

[WobblyHand]

You're not cutting dry are you? 1HP is a fair amount of power- I'm wondering if the controller current limit is mis-adjusted?
-Mark

Definitely not. Was a lot of cutting oil for the saw. Was a mess to clean up. Plenty of cutting oil ended in the tee-slots.

Could be mis-set. Just seems like it is not very strong at low RPM. Maybe there is insufficient feedback to the controller?

 

[WobblyHand]

Blondihacks (on YouTube) has a very similar mill. I think she does some work on her mill at various points, might not be exactly what you're after but may be useful for ideas.

Always a treat to watch her videos. I'll see if she has any upgrades or adjustments.

 

[markba633csi]

If I recall that's a DC brushless so it could possibly not be set optimally as far as torque compensation and so forth. I wish more tech info was
provided for these controllers but it seems they don't want you messing around with it. Try asking PM about it, maybe they can provide some adjustment info? I'm sure they would be pleased as punch to sell you another controller.

Another approach which I have used successfully is to mark all of the trimpots on the board with a Sharpie and start making small adjustments, checking the results each time. Assuming there are trimpots, that is. Some don't have any.
A DC brushless is just a 3-phase motor with a permanent magnet rotor, so like any 3-phase motor the torque will drop off somewhat at low rpm.
-M

 

[WobblyHand]

If I recall that's a DC brushless so it could possibly not be set optimally as far as torque compensation and so forth. I wish more tech info was
provided for these controllers but it seems they don't want you messing around with it. Try asking PM about it, maybe they can provide some adjustment info? I'm sure they would be pleased as punch to sell you another controller.

Another approach which I have used successfully is to mark all of the trimpots on the board with a Sharpie and start making small adjustments, checking the results each time. Assuming there are trimpots, that is. Some don't have any.
A DC brushless is just a 3-phase motor with a permanent magnet rotor, so like any 3-phase motor the torque will drop off somewhat at low rpm.
-M

I'll check to see if there are any adjustments on the board. Just seems a bit gutless at 150 RPM and under, which is the region that one wants to run a slitting saw. Above 400 or so, it seems ok if I keep the feed rate within the mill's abilities. Looking at the Blondihack's video there don't seem to be any trimpots that are accessible on the board. Everything looks potted. I will look, but not getting my hopes up.

 

[jwmelvin]

If think you may have more success with a pulley change. Changing the motor will need a new drive and VFD + 3-phase aren’t so good at low rpm torque.

 

[mksj]

You will also be pushing the limitations of the rigidity of the mill, have you tried a different tooth profile or smaller slitting saw. Also depends on the material and cut parameters. I would be hesitant to upgrade given the size limitations of the mill, in today's market you might be better off selling the current mill and going to something like the PM-30MV which they indicate should be in soon. Other alternative would be to change the belt ratios for lower speed performance.

 

[WobblyHand]

You will also be pushing the limitations of the rigidity of the mill, have you tried a different tooth profile or smaller slitting saw. Also depends on the material and cut parameters. I would be hesitant to upgrade given the size limitations of the mill, in today's market you might be better off selling the current mill and going to something like the PM-30MV which they indicate should be in soon. Other alternative would be to change the belt ratios for lower speed performance.

Yes, it would be pushing the rigidity of the mill. I could try a different blade in that size. Does having more teeth help or hurt? I do have smaller blades which I can spin faster. For what I was doing, I needed a rather deep 1" slot, which forced me to a "larger" diameter blade of 4" diameter, and lower speeds.

I did look at the PM-30MV. Hey, who wouldn't want to uprate their mill? Since the time I bought the PM-25, I was able to rig a heavier lathe into my basement. I am more confident about handling a larger machine.

Practically speaking, it seems changing belt ratios is the simplest, lowest cost solution. I will take a few measurements and see if I can fit some pulleys that might help.