Is my motor especially weak , or is it something else?

[bulgie]

Haven't used my Enco RF-30 clone enough yet to be 100% familiar. Most of what I've done has been larger cutters and steel, so my RPMs have been low-ish. So it's only yesterday that I finally had reason to run it at the highest speed, about 2500 rpm.

It does spin up to that speed eventually (confirmed with a Hall-effect tach) but it takes a couple seconds, and as soon as I start a cut, the RPMs drop. Even a light cut has it slow down a fair bit. Sorry I didn't take notes, but I think it dropped a couple hundred rpm, like down to 2200-2300? I can repeat the experiment if you need more reliable numbers than that. I was using a 1/2" endmill on wood, and not feeding it very fast at all. (Yes I cleaned the mill very well after cutting wood on it.) Not something I plan on doing much of, but I'd like to be able to spin it up like that to mill or drill aluminum with small bits. 2500 isn't even fast enough for some of your smaller drills in alu.

Nameplate on the motor says 2 HP. I got the mill used, but I'll bet this is the original motor. Date on the motor is 2002. Single phase, wired for 220. I've been impressed by how much metal it can remove at slower rpm, like a 3" face-mill with carbide inserts running about 1200 rpm, .050" DOC, it was loud and it shook some, but I didn't notice it slowing down.

Just wondering:

1. How normal is this? Are they supposed to be able to cut at top rpm (at least a light cut) without slowing down?
2. How bad is this? Am I burning out the motor if I let it bog down like this?
3. What's the most likely cause?
4. What's the most likely fix?

The belts don't seem too tight. Ok let's just say they're definitely not too tight, I even tried it with the belts on the loose side to see if that would fix it. Pretty sure the slowing isn't from belts slipping either, I think it's the motor slowing down.

Spindle bearings seem to spin just fine — when spinning it by hand, I don't feel any friction, to speak of. Ditto with the intermediate pulley bearing, plenty smooth.

I've been thinking of converting to 3-phase with VFD. If I do that, should I expect better cutting power at 2500 rpm with a nominal 2 HP motor? I mean, how much power do you guys have, and does it ever seem like not enough? I could throw more HP at it, but I'm sure at some point the bearings and/or the rigidity of the column etc become the limiting factors, so more HP doesn't buy you more milling, would you agree?

So many questions! I'd be happy if someone could tackle any one of those, don't feel like I'm assigning homework.

Thanks
Mark in Seattle

 

[markba633csi]

I would wager it has to do with the quality of the motor itself and there probably isn't anything you can do except replace it.
The speed decrease you are seeing is called "slip" and it varies with different motors
Spinning a spindle up to a high speed takes a surprising amount of torque and the frictional losses increase with rpm
Changing to a 3-phase motor with a VFD drive would be an improvement for sure- if you can justify the cost
Interested to see what others think
Mark in Mt. View

 

[silence dogood]

Does this motor have two capacitors in it? Have a hunch that it might be the run capacitor is bad.

 

[bulgie]

I would wager it has to do with the quality of the motor itself and there probably isn't anything you can do except replace it.
The speed decrease you are seeing is called "slip" and it varies with different motors
Spinning a spindle up to a high speed takes a surprising amount of torque and the frictional losses increase with rpm
Changing to a 3-phase motor with a VFD drive would be an improvement for sure- if you can justify the cost

Cool, I was thinking of changing to VFD + 3-phase anyway. I have it on several other machines, consider it practically a must. Changing speeds on the RF-30 is a pain.

Does this motor have two capacitors in it? Have a hunch that it might be the run capacitor is bad.

Yes, two. I don't think testing for that is within my capabilities, unless there's some simple way for the simple-minded. (If so, I'm all ears.) Paying to have this motor diagnosed and fixed wouldn't make sense since I'm hoping to replace it soon anyway, so any viable repair would have to be cheap.

Thanks guys for your ideas.
Mark

 

[tq60]

If you are increasing speed via belting, available torque is reduced by same ratio.

If motor is slow ramping up, it may have bad caps.

You can get a clamp on sp meter to measure motor current to see what is happening there.

If you have hvac or motor service companies near you, replacement caps are not that expensive to try.


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[pontiac428]

Capacitors are cheap. If your Enco/RF was made in the 1990s, then it probably had weak caps to begin with (it was a global problem for a period of time). You can replace the whole thing and use a VFD, or you can spend $30 on capacitors and be done with it.

 

[markba633csi]

Try replacing the run cap (the smaller microfarad value of the two) and see if there is any improvement in the slip
Doesn't cost much to try it anyhow- match the value and voltage of the original
-M

 

[pdentrem]

There is a difference between motors. Just because it uses the same number of watts as another, the power output can be very different. Horsepower vs ponypower. Usually imported motors are ponypower in my opinion.
Pierre

 

[pontiac428]

True, but I used to push my RF 2 hp hard. The motor can take more chip load than the column can, even with upgraded head bolts. The power complaint means the motor isn't running as it should.

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[silence dogood]

If the problem is a bad capacitor, it's a cheap and easy fix. Even if you decide to go with a three-phase motor, which is a good idea. Why throw away what may be a good motor? Surely, you could in the future find some use for it.