K&T Motor Running Backward Causes Damage?

Don Kinzer · Feb 16, 2018

In another post (http://www.practicalmachinist.com/v...ker-serial-number-registry-173409/index2.html) someone suggested that running the motor backward even briefly can cause damage. The installation manual for the 2CHL et al says "Check the rotation of the motor before installing V-belts." but it doesn't warn of possible damage from backward rotation.

So what is the consensus as to the possibility of damage if the motor is run briefly (without engaging the spindle clutch) in order to determine its direction?

thermite · Feb 16, 2018

Don Kinzer said:
In another post (http://www.practicalmachinist.com/v...ker-serial-number-registry-173409/index2.html) someone suggested that running the motor backward even briefly can cause damage. The installation manual for the 2CHL et al says "Check the rotation of the motor before installing V-belts." but it doesn't warn of possible damage from backward rotation.

So what is the consensus as to the possibility of damage if the motor is run briefly (without engaging the spindle clutch) in order to determine its direction?

De-clutched and "run briefly" actually meaning it needs only the least and shortest JOG you can create as far as determining direction goes. Tape or sharpie mark and a move of 40 thou or even less will tell you that in less time than full RPM/coast-down, too.

EG: No foul.

Ohio Mike · Feb 16, 2018

Don Kinzer said:
So what is the consensus as to the possibility of damage if the motor is run briefly (without engaging the spindle clutch) in order to determine its direction?

It depends on the model. All K&T mills need to turning the correct direction for the lube pumps to work. However *some* later models include a mechanism which is damaged or destroyed if the machine is turned backwards. I think its pretty easy, if you aren't sure just slack the belts before turning the machine on. Its free insurance.

alskdjfhg · Feb 16, 2018

If they have a clutch, don't think your damage it too terribly if your just checking motor rotation. But if it doesn't have a clutch, then it's got the little mechanism that can get damaged by incorrect rotations.

That's atleast how I understand it.

Miguels244 · Feb 16, 2018

alskdjfhg said:
If they have a clutch, don't think your damage it too terribly if your just checking motor rotation. But if it doesn't have a clutch, then it's got the little mechanism that can get damaged by incorrect rotations.

That's atleast how I understand it.

Ohio Mike said:
It depends on the model. All K&T mills need to turning the correct direction for the lube pumps to work. However *some* later models include a mechanism which is damaged or destroyed if the machine is turned backwards. I think its pretty easy, if you aren't sure just slack the belts before turning the machine on. Its free insurance.

These are the details.
Some machines with some mechanism.

thermite · Feb 16, 2018

Ohio Mike said:
It depends on the model. All K&T mills need to turning the correct direction for the lube pumps to work. However *some* later models include a mechanism which is damaged or destroyed if the machine is turned backwards.

IF... it really, really is that serious?

The motor doesn't HAVE to be allowed to move significantly AT ALL to determine what its direction of rotation wants to be.

Lock the rotor. Pulse it. See which way the "lock" was stressed. Normal running will follow the same direction.

If.. you have time on your hands? Do the re-engineering to fix K&T's f**k ups.

No fear. It won't become a career. These two represent only a few they ever made and they are well beyond being able to ever add any more.

Paolo_MD · Feb 17, 2018

This post from Archie describes well what this issue.

Paolo

USNmechanic · Feb 17, 2018

Don Kinzer said:
"Check the rotation of the motor before installing V-belts." but it doesn't warn of possible damage from backward rotation.

The motor won’t be damaged by running in either direction, but the components that it drives could be. By testing rotation before installing the v-belts, you eliminate the risk of engaging the clutch while allowing you to test the rotation of the motor.

Sent from my iPhone using Tapatalk

Ohio Mike · Feb 17, 2018

thermite said:
IF... it really, really is that serious?

The motor doesn't HAVE to be allowed to move significantly AT ALL to determine what its direction of rotation wants to be.

Lock the rotor. Pulse it. See which way the "lock" was stressed. Normal running will follow the same direction.

If.. you have time on your hands? Do the re-engineering to fix K&T's f**k ups.

No fear. It won't become a career. These two represent only a few they ever made and they are well beyond being able to ever add any more.

So you're betting an unobtanium part on you being able to bump the motor just the right amount? No thanks I'll slack the belts. Besides if its like most of the machines I've bought it probably needs belts anyway.

alskdjfhg · Feb 17, 2018

I've never seen the inside of the little "mystery" box that gets damaged. But it's not very large, I have one on my 5CK.

But looking at it hooked up to the 25hp that drives that mill, there is no way that I would try to start that motor with any belts no matter how slacked. The thing has a 5 (IIRC) vee belt pulley, any belt friction would probably be enough to mess up that little switch.

ramsay1 · Feb 18, 2018

Phase Rotation

Hello everyone.. I can't see why this is such a big issue if you have belts driving pulleys, just take the belts off and start the motor.. If the motor is running in the correct direction, re install the belts...If the motor is running in the wrong direction, change the rotation in the line...

We use to check 200 hp hollowshaft motors by bumping them.. Remove the drive key in the shaft, remove the ratchet balls in case the rotation was wrong and bump it..... If rotation correct just re install everything. If rotation is wrong, change two legs on the line...

Ramsay 1

gustafson · Feb 18, 2018

I know Bridgeport gearbox power feeds grenade if run backwards. Guess how I know......

When the German tech installed my DMG he had some widget with lights on it that enabled him set it up correctly. I imagine they know new from the factory how it is wired

ramsay1 · Feb 18, 2018

Phase Rotation

gustafson said:
I know Bridgeport gearbox power feeds grenade if run backwards. Guess how I know......

When the German tech installed my DMG he had some widget with lights on it that enabled him set it up correctly. I imagine they know new from the factory how it is wired

That "widget" was probably a phase indicator..They also made them with a wheel that rotated either right of left depending upon the rotation coming in from the line...

In a situation like yours, there is no way to disconnect the load from the motor so you have a 50/50 chance of wiping everything out unless you can know for sure which way to connect rotation .. We use to just take the drive loose and bump the motor to see which way it turned.. Some of our motors had ratchets on them that prevented wrong rotation.. We would take the balls out to prevent a possible "locked rotor" condition which is not good on a 200 hp motor.. Ramsay 1

jljim · Mar 11, 2018

All the K&T mills I've been around had an arrow on the drive pulley to indicate proper rotation. Just take the belts off and test run the motor. If your machine has the electric clutch like my 3ch, you can't turn the drive pulley backwards by hand, just as explained in Archie's post. Reverse rotation under power would certainly destroy the switch.

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K&T Motor Running Backward Causes Damage?

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