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 -
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?
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.
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.
Or do my precision boring jobs on the lathe, now that I know the mill
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.
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.
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.
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