Spindle And Motor Speeds

[mrbasher]

I recently purchased a PM940 mill and I'd guess this applies to most of the RF45 based units as well. When I made my purchase I ordered the 3 phase 1.5 hp motor along with WJ200 VFD.

I got everything hooked up and it works great so far. Seems very powerful for what it is. Though I have a few questions, hopefully some of you with experience might be able to help with:

What do you think a "safe" limit would be with regard to Hz? I realize the motor is rated at 60. But overdriving them seems to be pretty common practice.

Along with that, what about the spindle bearings? What speeds have you guys seen them be able to handle without grenading?

I asked Matt via email and as I suspected, he only recommended running both at the rated speed. Hard to warranty something and recommend it run at higher speeds. I thought I'd ask anyhow.

That said, I ran mine for a bit, not cutting, through each of the gears during testing. Kept it at or below 60hz. After not long, the spindle got pretty warm to the touch. Warmer than I figured it should. Motor wasn't warm at all. Is this normal?

The oil in the head wasnt all that clean looking to start with, but I wouldn't call it dirty. I do plan on changing it in short order. I also plan to change the stock bearings at some point, just not right now.

Given the kind of "stuff" that might be floating around in there, the oil, and the spindle being so warm... I'm inclined to strip the head down like I have the rest of the machine and give it a good cleaning and an oil change... Before the bearings see much abuse. I'd like them to last until I actually want to change them.

That said, I was quite surprised by how quiet it is while running, even flat out. Most of the noise is just the motor and it's fan. Granted, all the gears are submerged in oil.

 

[mksj]

I would probably go with 80Hz max, or around 2000-2200 RPM once broken in. It is not an issue for the motor to overdrive it , but the rest of the drive train could be a problem long term and you can get quite a bit of oil foaming at speed. I have a gear head mill which goes to 3K, but sounds like something is going to go at that speed so keep it below 2500. But should no be an issue for the spindle bearings.

The spindle bearings can be quite tight, and they can get very warm especially when new. After using my gear head for any length of time, the spindle/head gets very hot to the touch. The motor never gets warm, but then it is 3Hp. So this is normal at least in my experience. One thing I strongly recommend, is after 10-20 hours of use is to change the gear head oil. These machines often have a lot of post casting debris/metal filings, and there is also some material from the break in process. I would not tear the head aart to clean it. When replacing the oil, I use a high quality gear oil with anti-foaming additives. The foaming through the oil level window was significantly less, over the factory oil and I picked up about 100 RPM on the top end because of less gear drag.

 

[JimDawson]

If that is a 1800 RPM (nominal) motor, you are probably safe it at running it at up to 120 Hz, 3600 RPM. I normally run mine between 30 and 90 Hz. As for the rest of the machine, the spindle bearings should take 4000 RPM all day long if they are ball bearings, tapered roller bearings might want to run slower. But you may have to work up to that speed over time as the machine breaks in. As a new machine it's still pretty tight. I've had my spindle up to about 135° F for extended periods.

 

[Bob Korves]

There is no good reason to go above 60 HZ with a motor rated for 60HZ. Especially with Asian motors.

While you are cleaning things up, check the spindle bearing preload against the specs. I am not familiar with that machine, so do not know the details, but the manual should show the process. You should be able to hold your hand on the bearing area without it getting too hot to keep it there. Sometimes there is a run in procedure specified in the manual as well. If so, follow it before going to high spindle speeds.

First, before doing anything, talk to Matt.