Spindle regrinding limit

brian.pallas · May 24, 2018

This isn't for anything I actually need at the moment, just curious. When you regrind a milling machine spindle taper you lose drawbar force. Is it just once you lose to much drawbar force you need to then replace the spindle, or is there anything else that can be done to get drawbar force back?

johansen · May 24, 2018

add another washer to the bellevile washer stack.

Vancbiker · May 24, 2018

Some drawbars pre-load the bellevilles with a threaded retainer so one can adjust if needed.

DMF_TomB · May 24, 2018

add washers to adjust retention force. as springs get old and weaker quite common to add shim or washer

DavidScott · May 24, 2018

You can also chrome plate the taper to build it back up, but that is after some pretty extreme grinding. If you are just cleaning up normal wear then a regrind or three won't matter, you should only lose half a thou or two Z axis movement at most when cleaning up a taper. I would never add to old belville washers, just replace them all. Perhaps overkill but after working with a Fadal I am stuck with that mindset.

brian.pallas · May 25, 2018

Thanks, makes sense. I had assumed there was a way to get drawbar force back.

Rockyr49 · May 29, 2018

From what we see, unless the drawbar is weak before hand, grinding the taper will have little effect on the pressure. If we take .001" off of the taper, the Z difference is .0034". That's why we check drawbar pressure before grind if possible. It could cause a problem, but I ground LOTS of tapers multiple times with no adverse problems. I'm not so sure about adding a spring or shim. Seems to me that would create a problem during unclamp. Quite possibly could break the washers.

Rocky
Spindle Grinding Service (retired).

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Spindle regrinding limit

brian.pallas

Hot Rolled

johansen

Stainless

Vancbiker

Diamond

DMF_TomB

Diamond

DavidScott

Diamond

brian.pallas

Hot Rolled

Rockyr49

Aluminum

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