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60Hz hum/vibration from Sherline 4000 motor. Normal??

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robmack

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#1
Hi,

First post here at Hobby-machinist. Thanks for indulging.

I joined because I recently bought a Sherline 4000 lathe from a local private seller. It is a DRO model with the "B" package and numerous additional accessories, including 21 QCTP holders. It's completely unused; even has the protective coating on some parts and original unopened packaging on others.

In any case, my real question is about the motor on this mini-lathe. I turn it on and the motor works fine, including speed control. However, there is a 60Hz hum coming from the motor at all speeds and this translates to a 60Hz buzz through the motor mounts. I know the motor is DC and my expectation is that the motor would be completely silent when running.

Is this normal behaviour with other people's Sherlines or do I have to contact Sherline for service?

- Robert.
 

mikey

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#2
Robert, you might call Sherline and ask them. I own a long bed lathe and I don't hear any buzzing from the motor. The motor does hum but you would expect that from any motor. My mill doesn't buzz, either.

It just occurred to me that the belt or pulley may be touching the belt guard; that can cause a buzz. Have you check for contact?
 

chips&more

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#3
Welcome, how do you know it’s at 60Hz? Does it have the same level and pitch of sound at any speed setting? Is the motor running at your selected speed setting correctly or with an erratic speed/rpm? DC motors are not typically silent when running, only when they are turned off. I have witnessed many Sherlines that will have a motor growling sound more so at the very slow settings of the speed dial. I have never witnessed a silent running Sherline motor at any speed setting. It’s a motor, and would expect some kind of noise from it.
 

markba633csi

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#4
Your speed controller is making rectified AC not pure DC so there will be hum at 120 cycles.
You could try some rubber mounts on the motor.
Mark S.
 

robmack

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The hum does not vary as the motor speed varies so it can't be related to the motor, spindle or driveline. The motor maintains speed when set and the intensity of the hum is constant at all speed settings. I called Sherline and spoke with them about this. Their recommendation was to chuck some material and test the lathe with my work to see if it's being affected. If I'm still concerned after doing this, then I could return the motor/headstock to the factory for examination.

I visited the local Sherline dealer here in town and did some testing on their showroom model. It's doing the same thing so blame lies with me. I guess I'm just overly sensitive. This humming is not a problem after all. Thanks to those who answered.
 

markba633csi

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#6
Not to get too technical, but the power to the motor is a fixed frequency but a variable "duty cycle", therefore you have the same frequency hum at all speeds. Might vary in intensity somewhat from fast to slow.
Mark S.
 
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