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NEED HELP- MAZAK QT15 sloppy indexing


Apr 30, 2019
I'm having a recurring issue with my QT-15 , 12 position turret working loose and not locating properly.
I can temporarily solve the problem by tightening the tension nut on the center spindle, but after a few weeks it's loose again.
I do tighten the pinch screws, but maybe not enough to keep the nut from backing off ?
Or is something working loose at the other end ?
Watching the turret as it indexes, I can see there is rotational play between the turret and spindle as if there's a key or keys that are worn allowing for the slop.
Even though less than a 1/8 of a turn fixes it, I don't want to keep tightening and tightening for fear of stripping something at the other end or God knows what.

So It would be very helpful for someone who's gone where this man hasn't to advise what perils will I get into by removing the turret to inspect the internals.
Does the turret just slip off once the center nut is removed?
How heavy are these turrets to begin with ?
What should I look for or expect to find once the turret is removed ?
Besides the slop issue, I need to figure out how to stop the coolant from squirting out where it shouldn't be. That can't be good for any internal bearings etc.
TIA for any and all replies.
I've had mine off but it's been a while. I made the thread linked below at the time.
The main large turret nut is all that holds the turret on the shaft, so if you remove the nut, you can wiggle the turret off.

Make sure your machine is powered down when you remove the nut, else the clamp tension will make removal difficult.

The nut does not clamp directly on the turret; it actually clamps on a twin-tapered-ring coupling. This coupling may have slipped inside the turret, or is slipping. There are about 10 or 12 small bolts that squeeze the two coupling rings together to lock them, just around the large main nut. Check these bolts and the coupling itself. You can remove it to clean and inspect easily if you remove the turret.

If the twin-cone coupling has slipped inside of the turret plate, the turret will turn a bit when clamping. If the main curvic-coupling has slipped inside the turret plate, the turret will turn slightly when clamping as well.

After a crash if your turret is off-center in "Y" direction, most likely it's because the turret plate has slipped on it's curvic-coupling. You have to loosen the 8/10/12 curvic bolts (~10" BC) in the turret and pull/beat it back on center. Make sure the counterbores and holes are clean for the curvic bolts, as the only slack you have to move the turret in "Y" is the clearance in the holes around the bolts.

The turret shaft itself rotates inside the hydraulic clamp piston, and over time the piston and/or shaft can wear, causing the turret to drop noticeably when unclamped. This may cause abnormal wear on your curvic-coupling teeth, otherwise it don't hurt too bad as long as the turret clamps back true, but eventually you may have to replace the shaft and/or piston.

I machined a turret-clamp cylinder, lid, and piston for a QT15 one time, as Mazak was just outrageous on the part prices!

The shaft would have to be purchased though, too complex with splines and precision ground diameters. The hardened shaft is usually good though, so if you needed a new piston and/or cylinder, they are fairly easy parts to reverse engineer and make.

The turret weighs 75 lbs. maybe? Take all your tools and bushings out to make lighter. I use a 4-5 foot 2x8 wedged under the turret, using the long end of the 2x to lift and wiggle to remove/install the turret on the shaft. You can also slide the turret down this board to the front of the machine, so you can carefully lift it and set on the workbench.

A mod I highly recommend for any hydraulically rotated-and-clamped turret is to install a flow control valve in the pressure circuit feeding the turret. This way you can slow the clamp/unclamp and rotational speed by adjusting the valve.

I slow all my Mazak turrets down to about half-speed rotate and C/UC, much easier on the hydraulic motor, the piston and turret shaft, and the curvic coupling!

Another couple of highly recommended "ToolCat Mazak Mods" is to slow the spindle accel/decel rate, and lower the max rapid parameters.

Reliability is what you're after in these old classics....

Good luck with it, the QT 15's are workhorses!

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