# help: the gears in my 3900 failed



## garobers@yahoo.com (Oct 27, 2013)

Hi everyone, i have a LMS 3900 High Torque mill and the other day i was cutting some steel when the end mill stopped. Most of the time just raze the end-mill and restart the motor...this time the end-mill would not respond. the motor runs but the spindle's shaft leans and the spindle does not move. Any one ever rebuilt one of these? Another question is the new belt drive better than the metal gears? George


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## wrmiller (Oct 28, 2013)

I've not rebuild a gear driven head, mine never got to the condition you describe.

But I can say that the 3960 I have now benefits significantly from the belt drive: quieter, smoother, etc..

Your head is the gear-driven one with the hi-lo range on the side?

Bill


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## pdentrem (Oct 28, 2013)

Is there a shear pin or did the key fail, fall out, set screws back off? Might be that simple.
Pierre


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## DMS (Oct 28, 2013)

My 3900 had a belt drive stock. I wasn't aware that they offered a version without. I would recommend pulling the top of the head apart (it's straghtforward to do, just watch the cables on the motor, don't let the motor hang by them) and see what's going on. You might have broken or slipped a belt, could be the motor slipped in it's mounting and the belt is just not engaged anymore.


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## garobers@yahoo.com (Oct 29, 2013)

thanks everyone!!

i have not dove into the actual gears yet. I was trying to collect some intel before disassembling the unit. _s the belt drive as good (positive) as the gear drive? i would think that a belt drive would slip.

George_ )


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## wrmiller (Oct 30, 2013)

It's a toothed belt. It won't slip.


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## garobers@yahoo.com (Dec 15, 2013)

*Re: help: the gears in my 3900 failed and the belt/gear modification pulleys dont fit...never ends*

Hi everyone,
    i purchased one of the new belt/gear modification for my 3900 and none of the pulleys fit the shafts. I am contacting LMS tomorrow. I'll keep everyone informed.  
Thanks
George


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## garobers@yahoo.com (Dec 15, 2013)

wrmiller19 said:


> I've not rebuild a gear driven head, mine never got to the condition you describe.
> 
> But I can say that the 3960 I have now benefits significantly from the belt drive: quieter, smoother, etc..
> 
> ...



my 3900 is belt driven (single drive) "metal gear" model.


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