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VFD alternatives for mill or lathe

MeanMachine1980

Aluminum
Joined
Dec 30, 2017
Hello
I have a lathe with an older 2hp ac motor. I also have a 3 phase 2hp motor for the lathe. I would like to follow what 98% of others do and install a VFD to the 3 phase motor to get "fine tune" spindle speed. I could also take advantage of the programmable starting and stopping rates within the VFD.
The only problem is that every VFD driven motor I've seen online in videos has that common nasty whine. I know that increasing the carrier freq somewhat decreases it but not totally and at a high cost to the motor and vfd.

Has anyone used a VARIAC? It changes the speed with voltage instead of frequency. They are used a lot on smaller applications but I've never heard one using it in a high torque application like a lathe.

Any info is appreciated.
 
Hello
I have a lathe with an older 2hp ac motor. I also have a 3 phase 2hp motor for the lathe. I would like to follow what 98% of others do and install a VFD to the 3 phase motor to get "fine tune" spindle speed. I could also take advantage of the programmable starting and stopping rates within the VFD.
The only problem is that every VFD driven motor I've seen online in videos has that common nasty whine. I know that increasing the carrier freq somewhat decreases it but not totally and at a high cost to the motor and vfd.

Has anyone used a VARIAC? It changes the speed with voltage instead of frequency. They are used a lot on smaller applications but I've never heard one using it in a high torque application like a lathe.

Any info is appreciated.

"98%" of those making a public fuss about it may use a VFD. Far more who just make chips do not.

Use of a Variac wants a different type of motor. One that is Voltage sensitive, rather than frequency locked. Series or "universal" wound. Even DC.

For more than a hundred years it has been easier to "fine tune" depth of cut and selection of feed within the most appropriate band of mechanically selected ratios.

Continuously variable spindle speed was costlier, more complex, hence less common.

Damndest thing, though.

Chips got made anyway. Sometimes in amounts that needed narrow-gage railcars to carry away.

Who ever wudda think it?

Might be better-off to run what yah got, and spend the VFD money on music of choice, "whine" optional if not into "Country" music.
 
The only problem is that every VFD driven motor I've seen online in videos has that common nasty whine. I know that increasing the carrier freq somewhat decreases it but not totally and at a high cost to the motor and vfd.

Most on-line videos are of the nature "gee wiz, look what I have here".

Raising the carrier frequency up to some point may reduce the singing at the expense of increased semiconductor switching heat. It's better to reduce the carrier first and see if that is acceptable.
 
Increasing the carrier frequency is actually BETTER for the motor, it just increases the heat in the DRIVE. It can also exacerbate any standing / reflected wave issue, but in general with machine tools, the cable distances make that irrelevant. So it means de-rating the drive, usually no more than one size. If you have already de-rated a drive to use single phase input, you need not worry about it at all.

The whine is annoying to humans and dogs, then if you increase the CF, it's only dogs. But honestly, MOST of the time the noise of the machine itself drowns it out, you will only notice it when the machine is not actually doing anything. If you wait until you are over 50 like me, you don't hear it any more.
 
Increasing the carrier frequency stresses the motor windings. A increase from say 5k to 20K just to get any switching sounds out of my audible range is something I would not do. I prefer to float around 5k to 8k and leave it there. Probably depends on the drive too. Since I don't own any cheap drives I can't compare with any.
 
Fans on my ABB ACS800 make more noise than the motor "whine"
(and its not same kind of constant pitch whine as most vfd's, its more random spread spectrum style than constant whine)
 








 
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