Runout problem

I bought a used VMC and I'm getting a lot of runout on tooling, sometimes as much as .013 TIR at 4" from the gauge line. I've installed new bearings and when I check the spindle bore there is minor runout from end to end, I've traced the 7/24 taper over the length of the taper and there's never more than .0005 radial TIR and about .001 from the small end to the gauge line. I will, if I can figure out why I get the excessive runout, get the spindle reground anyway but why so much runout, where is it coming from, any suggestions?

Have you blued the taper, and have you checked the tool retention?

I have blued the taper and as the indicator shows, it's very slightly larger than it should be at small end but nowhere near where enough to permit the wild runout I'm getting, just for a better idea where the issues are I stuck four pieces of plastigage on a tool and clamped it and the results basically confirmed the indicator readings. And no, I haven't checked the drawbar pull strength but what I was considering is if the drawbar could be pulling unevenly.
Part of mot checking how much pull on the drawbar is that the spindle is a BT35 taper so finding the load tester will be a challenge in itself.

Samo a-game with the toolholder installed in both the thisaway and thataway positions in the spindle?

Also worth checking the flanges and keys / keyways on both the spindle and toolholder.

I'm getting a lot of runout on tooling, sometimes as much as .013 TIR at 4" from the gauge line

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Is the runout consistent? If you take the tool in and out and in and out, does the runout stay the same?

If you flip it around 180, does it flip to the other side (minus or plus a small amount due to taper wear).

Are your tool holders garbage?

I had this on a fadal, it had about same runout as yours same type loose on the small end. Blue wasn’t that bad. I used a bridgeport jig grinder attachment and programed the taper cleaned up the taper and only lost about .0120 on the gauge. Now the runout on a test bar is less than a half thou at 8 inches big improvement. Found out to make sure you always make the same movement of your axis or it can effect the taper.
Read about this on another post on here that it can be done ,so out of desperation i gave it a try and it worked.
Used a cbn jig grinder pin and set the angle of the grinder spindle as close to the 7/24 taper i could get. Cuts great now and tools last much longer.
If it didn’t work was just going to buy a new spindle as fadals are not to bad.


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I've tried flipping the toolholders and several different ones with the same results including checking the runout on the ID of collet holders with basically the same issue. As you can imagine, being BT35 holders none are new but I have some that show no discernable wear and still have the problem.

Turbowerks said:

I used a bridgeport jig grinder attachment and programed the taper cleaned up the taper and only lost about .0120 on the gauge.

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I have considered that, I have a toolpost grinder I could set up, but am concerned about getting the taper exactly right, a little off and I'd be in a worse position and still have to pay someone $1200 to grind it anyway.