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Variable TIR on Super Chuck

I recently bought a Super Chuck model 14N for a floor drill press. This chuck has a capacity of 0" to 1/2 ". I have been checking the TIR using jobber length drill bits in the 1/8" to 1/4" diameter range. I noticed the TIR seems to depend on how hard I tighten a drill bit in the chuck. For example, if I tighten it just using my hands without the key, the TIR is under 0.001, but if I fully tighten it using the chuck key the TIR climbs up to 0.004 or so. If use a #1 drill+countersink bit instead of a jobber drill bit, the TIR change is even more dramatic with a shift from under 0.001" to about 0.008". These measurements are all at the top end of the bit, just under the chuck jaws. Is this normal behavior for these chucks, or perhaps I got a lemon?

Reply to
Tidrix
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Does a "Super Chuck" have a key? I tighten my keyed chucks progressivly in all three holes twic around. This seems to help me.

Reply to
Tom Gardner

I went through some of this too on the same chuck. Some of my problem was how I seated the chuck on the arbor adaptor. I reseated on the jt33 (?) a couple of times until runout was I recently bought a Super Chuck model 14N for a floor drill press. This

Reply to
larry g

It is a Jacobs ball bearing Super Chuck and it has a key. When tightening with the key I have tried using a single hole as well as all three holes with similar results.

Reply to
Tidrix

Now that I think about it, I have one of those chucks too, in a lathe. I don't know where I got it but it was used and always had run-out. I Just thought it was worn, maybe accuracy is not it's inherent strength. I only use it when I really, really don't want a bit to spin in it 'cuz I can tighten the shi* out of it.

Reply to
Tom Gardner

I don't have a Super model, but I've noticed on a couple of my larger chucks that when small diameters are chucked, the jaws can distort outward. The grip pressure is near the tips of the jaws, instead of back inside the chuck body. You could try chucking a drill blank (or a straight locating punch) fully seated in the chuck, for another check. I think that when the small drills (particularly short ones) are only partially inserted into a big chuck, the jaws don't hold true.

When I need to use small drills without changing to a smaller chuck, I use arbors to hold them (the arbor is seated more deeply in the chuck). A setscrew in the arbor holds the drills securely, although the drill needs to have a small flat spot ground in it.

WB .............

Reply to
Wild Bill

I've drilled tens of thousands of holes with drill chucks, and rebuilt 20 or so chucks at work. Other than a few lucky ones, I don't think it's in their nature to be all that accurate. Albrecht keyless chucks have a fairly precise guide system for the jaws and seem to run pretty true most of the time. If I have an occasion to reduce the runout on a drill, I usually use a collet if the drill diameter matches it, or I select a pilot drill that does. Collets already match the diameters of center/combined drill/countersinks.

RJ

Reply to
Backlash

The point of the ball-bearing chucks is higher gripping capacity on account of reduced friction in the tightening works. The jaws fit looser than in precision keyless chucks so there's bound to be more slop. Also the high gripping capacity makes it easy to spring and permanently damage the jaws by over-tightening the jaws on a bit that doesn't reach all the way to the back of the jaws. If your chuck is not new it has probably suffered that abuse.

I'm sure happy with them though and would not use anything else for heavy drilling.

It should not be a problem with a #1 center drill but the larger double-ended ones are a problem, as the smooth part of the body doesn't reach the back of the jaws.

Bob

Reply to
Toolbert

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