regrind spindle

I have a runnout problem in the spindle on my CNC mill. means small tooling, like endmills under 1/8" diameter break constantly. Driving
me nuts again this week.
Last year, I took the spindle apart and installed all new bearings - no help.
I had read that the entire spindle cartridge could be sent in and have the 40 taper reground to be exactly true. Not sure where a place like this might be.
Any suggestions on my next step here?
Karl
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Karl, how do you know, how did you prove to yourself that you have a runout problem, and not, say, a following error problem.
i

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On Fri, 13 Feb 2015 18:34:20 -0600, Ignoramus4453

I'm an engineer and a machinist, so I measured it <VBG> More runnout at end of long tool holder, average about 1.4 thousanths. Best tool was my hole centering guage, that way all you have to do is hold the unit while rotating the quill by hand.
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I'd measure the runout at the endmill shank, also that of the 40 taper ID, and their deflection under a side load from a spring scale, as I did this morning for Robobass.
The quill shaft on my mill is worn and deflects when extended, meaning I have to bore precision holes to final size by raising the knee. -jsw
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wrote:

Or do my precision boring jobs on the lathe, now that I know the mill bores tapered.
It was only a few tenths, which mattered because I was rebushing a hydraulic gear pump. If I rebore my air compressor I'll have to use the knee anyway since the quill travel is only 3".
It's an early model Clausing 8525 with a poorly designed quill clamp which they changed later. -jsw
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On Fri, 13 Feb 2015 18:09:02 -0600, Karl Townsend

Greetings Karl, Some of the tool holders I have run out too much for small cutters. Really, a 1/8 cutter should run true within a tenth, and a few of my holders for small tools run out about 3 tenths. I made an eccentric bushing for a small cutter but I don't like holding cutters in bushings that slip in. So I am considering putting the tool holders in the machine and boring them large enough to take a pressed in bushing. Then boring to bushing in the holder in the spindle. Since all my holders ALWAYS go in the same way the holder should always run true. Eric
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Karl Townsend wrote:

If you can spin a holder in the taper (maybe by removing the drive dogs temporarily) you can get a good idea of what is going on.
Two ways to do it. One is to smear a VERY thin film of spotting dye inside the spindle, and then work the holder in and give it a small twist when gently seated. Turn it less than 1/8th turn, then pull out and look for a streak of dye on the holder. Then, you have to figure out where in the spindle the high spot is. The clear indication will be one side of the holder has a wide print of dye, the other side has just one small mark.
The other way is to coat the holder fairly lightly, and wring it into the spindle. Then, you need a REALLY good light to see up in the spindle. You may need a mirror to keep from twisting you neck into a knot trying to see into the spindle. This should point out any bumps in the spindle taper. Any big dings will produce a "crater rim" around the ding. So, a bull's eye pattern is for sure what you are looking for. You may be able to remove these with a Swiss file or a curved piece of steel working it like a scraping blade on the ding. Don't worry about leaving a tiny low spot in the spindle taper, it will not affect the accuracy at all, but a high spot will cause the tool holder to rock in the spindle, that's even WORSE that a little eccentricity. Although, it sounds like you have MORE than a "little" eccentricity going on there.
Jon
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