Problems with power tapping head

Someone gave me a power tapping head for free, but I'm having a problem with the taps running out a lot (+/-0.025) in the chuck. I thought it was just a simple chuck... put the tap in and use wrench to tighten the nut and off you go.

The taps are held in a 3-jaw arrangement with locking collar to tighten. I cleaned these jaws and stoned to make sure no burrs were interfering and fixed one of the springs that had popped out of its hole in between the three jaws. In addition there is also a square drive screw above that when turned opens and closes an additional pair of round opposing 'jaws'. These 'jaws' have a half round cutout in the lower side that hits right on the square end of the taps. I tried tightening this down on the taps as well, but it didn't help at all.

I couldn't find a copy of a manual for this specific chucking setup so I could figure it out. Is anyone familiar with this particular unit and what I'm missing?

I have a couple those Ettco tapping heads. The jaws that adjust to hold on the flats of the tap shouldn't have the half moon cutout, that's wear from not having them adjusted right and the tap spun. I couldn't get a clear picture of mine but I think you can tell what they should look like.


The round parts are soft so you can either weld up and reface them or cut new keyways 90 or 180 degrees away from the originals to rotate them.

The other thing to check is to make sure the spindle coming out of the head isn't bent and running out.

I cropped your picture with the mirror. It looks like the jaws are worn uneven. (like the other member indicated.)

OldMachinist said:

I have a couple those Ettco tapping heads. The jaws that adjust to hold on the flats of the tap shouldn't have the half moon cutout, that's wear from not having them adjusted right and the tap spun. I couldn't get a clear picture of mine but I think you can tell what they should look like.
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I can't quite make out from your picture 'oldmachinist', so the two opposing jaws that grip the tap flat shouldn't have ANY cut out at all? If that's the case I'll probably just rotate and cut new keyway at 90 degrees. I'll have to mill those this weekend and see if it helps.

To 'DAN_IN_MN': I see what you're saying from the picture. It doesn't look as bad in person as it appears in the picture. I think it's the angle of the mirror. When I tighten the nut down to bring the three jaws together they really look more uniform. That said, the runout is bad enough that the jaws may very well be worse than I thought.

Yes, the face should be flat. Cutting new keyways will work.