100Hz hum: Motor noise?

[discosdecorte]

Caused in all probability by few thousandths of an inch/mm undersize of the Motor Drive Capstan (Being all it needs to cause this) would be my Best Guess [...]

Some cheap DIY solutions for slightly increasing the capstan width: https://www.quora.com/How-do-you-increase-a-shaft-diameter-by-a-small-fraction-of-an-inch-like-1-8

Best regards,
Fer

[EposLab]

The motor is a sync 10V and is directly connected (through a switch) to the main transformer. Using a speedcontroller (vfd) i run the lathe at 50hz , then the speed is abit faster than 33rpm. When i run the lathe at 60hz then the speed is lower than 45rpm . Capstan looks ok , little dirt but not worn to my eyes. The lathe is already packed and soon will be on way to Jesus! I know he will treat it well!

[markrob]

Are you sure the motor is a true synchronous type? On many lower end lathes, they used a simple AC induction motor. It will still respond to a VFD, but due to the way that type of moto works, it does not have a flat torque/speed curve.

How far off is the speed from 33.333 RPM at 50 Hz line frequency?

Given that you have a VDF, I'm not sure why this is an issue. Just dial in the speed and you are done.

Mark

[EposLab]

Im not really sure but i i i did locked it to 33rpm when it was running @48Hz.
This mini lathe ment to be portable and thats the main reason i bought it. I'm planning to use it in places without the worry of carrying/missing an vfd.

[markrob]

I see. That looks to be about 4% off. That's almost a semitone. Probably a bit more than is reasonable. The fact that its fast, indicates that its not the motor as it would typically slow down with age as bearings gum up with dirt and age, increasing load. You would have to reduce the motor shaft capstan diameter by 4% to slow the speed down. That's not much. For example, if the diameter is .250", you you need to reduce it to.240". Probably more than would be gained by a good cleaning and polishing of the shaft.

[EposLab]

The fact that its fast, indicates that its not the motor as it would typically slow down with age as bearings gum up with dirt and age, increasing load.

This lathe originally runs @45rpm so when i run it at 60Hz , speed is lower than 45rpm.

[discosdecorte]

The fact that its fast, indicates that its not the motor as it would typically slow down with age as bearings gum up with dirt and age, increasing load.

This lathe originally runs @45rpm so when i run it at 60Hz , speed is lower than 45rpm.

It happens the same with mine. I went the cheap way using some aluminium tape and a piece of heatshrink tube to achieve the right speed. But I'd love to find a more stable solution, of course.

Best regards,
Fer

[Jccc]

Hello,

i am having this same problem with my recordings using my Presto 6N lathe with Neumann cutting head.

Has anyone found a way to dampen the moto sound / vibrations coming from the Presto motor?

Its really audible in the recordings when i turn the volume up. its sort of like a low frequency tone.

i was thinking maybe a thick rubber mat on the platter? Or maybe use some sort of rubber to put where the motor is hanging from?

[Soulbear]

Hello,

i am having this same problem with my recordings using my Presto 6N lathe with Neumann cutting head.
Has anyone found a way to dampen the moto sound / vibrations coming from the Presto motor?
Its really audible in the recordings when i turn the volume up. its sort of like a low frequency tone.
i was thinking maybe a thick rubber mat on the platter? Or maybe use some sort of rubber to put where the motor is hanging from?

BSR DR33C Restoration9.jpg

Maybe by using Longer Anti Vibration Mounts as used here on the Motor of my BSR DR33C Lathe Restoration?? They have great shear properties and will be under "Compression" so the longer the mount the greater the "Damping" Any height variation caused by increasing the length of the mounts can be compensated for by utillising simple "Z Type" Metal brackets made to the correct length. I could not be bothered to make new "Z" brackets, instead, I simply cheated and used the original brackets, but added a "Spacer" (My Bad!!")This would save changes having to be made to the Capstan on the Presto. A possibly very simple remedy and as "Cheap as Chips" so maybe worth a shot to rid you of this problem??
Best Regards Soulbear

[Jccc]

that looks like it will work!
Where did you find the parts for that?

Did you have to find new dampen material for it?
I can probably go to the local hardware store to get the longer bolts and stuff.

Thanks for the help