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ESM-59 with DC motor (noisy)

jkycia

Plastic
Joined
Oct 30, 2020
Hello All,
So I have replaced the spindle bearings of my ESM-59. That worked out very well.
I have had a problem with my DC motor that is originally came with (Eaton WC 1002 G640
1 HP 1750 RPM 90V DC motor).
I had replaced the bearings on that, and it did improve things but in the end, it always had a vibration, resonance at 50% speed and more above that. Then when running, connected to the lathe it made the whole table and lathe shake. I measured the runout on the motor shaft and it seemed too large.

I decided to get a new DC motor with what I thought were the same specs, and thought that this would resolve all the trouble.
Rookie mistake? So I ordered a Leeson model 108022.00, 1HP, 1750RPM, 90V DC motor. This motor now spins
without resonances but it seems much louder. There is always a very loud transformer hum.

Is that the fault of floppy windings in the new motor? I did not measure how loud the Eaton was, but this one, I set my cellphone 6 ft away and measured 55dB when it just starts spinning and then it quickly goes to 60 dB and stays there for the rest of the RPM range. Looking at the noise peaks they are all harmonics of 120 Hz.

Is it a problem of my motor speed controller? It is a Dayton 2M171E SCR controller.

Is that just the way it is?

What are solutions?
Wear ear protection?
Put a box around the motor?
somehow decoupling the motor from the table (it is rigidly mounted to the bottom of the wooden tabletop)?
change the supply?
Adjust something in the supply?
other?

How loud are your small lathes? 60dB at 6ft?


Thanks
 
Three phase motors are very quiet, even if run from a VFD. Hardinge was particular about balancing their motors and other rotating parts. Once the OEM parts are gone, you are on your own to design a drive system that works well.

I only use DC motors on my watch lathes and accept that they make noise, mostly from the brushes rubbing the commutator.

Larry
 
This has been puzzling. The new motor is so much louder. I took the motor off the frame and ran it sitting on the floor. It was then quieter.
Then I lifted the motor off the floor and the transformer noise went completely away. Maybe just brushes noise.
In replacing the motor, I made a very rigid bracket for it to screw into and the table top is wood. I think it is just amplifying the vibrations. I will see if I can put some sort of vibration damping on the mount. maybe sandwich some rubber pad between the bracket and the wood table.
 
I had one light duty lathe that the single phase motor pulses caused vibration and surface finish issues, we changed to a DC motor to solve the problems. I remember it as very quiet.
That said we have a AHC that was always noisy with the motor that Omniturn installed. We added sound absorbing foam panels to the flat surfaces inside the cabinet and that helped a little. Later we replaced the motor with one with a cast iron frame that helped a little more. We thought the aluminum fins on the motor were ringing because of the VFD.
The biggest decibel drop came from replacing the lower belt.
Original Hardinge lathes have so many vibration dampers between the cabinet and motor it is not even funny.
 
update: I hung the motor off of 4 small rubber mounts with 1/4-20 studs on each end.
these were rated for 35 lb pounds (vertically). I think these are too weak in the lateral direction. The motor is wagging around (at about 2Hz) more than I would like when spinning. Also, I put dynamat on the motor, that quieted it down a little.
Together they lowered the sound from initially (55dB low RPM and 60dB at high RPM) to now (48 dB low rpm and 53 dB at high RPM).

I don't think anyone would comment how quiet it is right now, but it is not stupidly loud like it was as before.
I need to get better damper. Maybe stiffer. Maybe I should somehow position two rubber mounts horizontally to limit vibrations in the lateral directions.
 
I looked at the voltage coming out of the Dayton motor speed controller. It uses an scr. It has spikes either every 1/60 or 1/120 of a second. Looking it over with a friend we determined that the controller was ok but that my new motor had less inductance than my old one and that is why it makes a louder hum. ...maybe that is what people were saying here.. In any case, We solved the problem by putting a large iron core inductor in series with the DC motor. That significantly reduced the hum.
 








 
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