Hurco KMB-IS CNC update

Somewhat off topic, but maybe somebody has some useful suggestions.

The Hurco has always exhibited noticeable spindle runout. Assumed it was the bearings. I've also learned its risky to "ass"ume things.

Took the head apart and extracted the spindle. It appears that most of the wobble is due to some sort of angular displacement of the taper off the spindle centerline. Not sure how this could happen?? Crashing the spindle into the table maybe?

There is a new spindle with the matching part number on Ebay. $1800. Midwest CNC has reconditioned spindles for about $2000. Its a bit difficult to spend that kind of money on the old beast.

I've heard that tapers can be reground. Don't know how that works.
Perhaps somebody has an old Hurco rusting away in their boneyard and willing to donate its spindle to a good cause image missing /media/kunena/emoticons/smile.png.
Anyways, just tossing this out there.

It's possible to regrind a spindle in-situ. The danger is that if you remove too much material then the tools will sink too far, and either bottom out, or not be properly clamped by the drawbar.

The amount removed may be small, but it is mutliplied axially because of the taper angle.
It's not as bad with a 7/24 taper like SK/BT/CAT as it is with a lower angle taper like Morse.

Here is one way to do it, using a Dremel.



It's critically important that the point where the grinder touches the spindle is exactly on the XZ plane, or the taper angle will be wrong.

Taper angle is atan((7/2)/24) = 8.29714 not atan(7/24)/2 = 8.130
I mention this as I made a few tool holders to the wrong angle by getting this wrong and you will find the same mistake made in various places on the internet.

Taper regrinding works well, sometimes better than a new spindle. You are using the bearings for that spindle and eliminating that run out also.