Yeah, that does have a "ring" to it. We tend to forget that metal does distort when we're using it. Got a great lesson in that last night with a 1/8" endmill.
Yeah, that does have a "ring" to it. We tend to forget that metal does distort when we're using it. Got a great lesson in that last night with a 1/8" endmill.
No room, and we need a multitude of sizes. Each hole is 1/2" deep in hard Beech at 20,000 rpm in
That's how I've always done it. I often wiggle the drill after hand-tightening, to make sure that it is properly centred, before using the chuck key.
Leon
Yes, a Jacobs chuck was the subject in the OP. But I would have been surprised if the thread didn't drift at all*. That's partly why I copied the question to this newsgroup: to see where the conversation would lead.
(* It occurs to me that in a metalworking group, "thread" and "drift" are easily misconstrued. I was referring to the tendency of a conversation to wander away from the original subject. )
I bought a new import 3 jaw lathe chuck a couple of years ago and it came with a final inspection chart.
I noticed that in the section of that chart where the runout of a test rod clamped in the chuck was recorded, there was one data line for "master pinion" and another for "any pinion".
The runout written on the line for "master pinion" was less than the one for "any pinions".
Looking at the chuck, one of the three pinion tightening holes had an "M" stamped on the chuck body next to it.
I checked it myself after the chuck was mounted, and the inspection chart was correct. Tightening the "M" pinion gave less runout than tightening either of the other two pinions.
I checked another 3 jaw of mine and found a similar runout difference when tightening different pinions, so I stamped an "M" next to the one which gave the lowest runout.
Course now that I just finished writing this, it occurs to me that might only hold for tightening the jaws on a piece with a specific diameter, and that tolerances and wear on the chuck scroll may well make one of the other pinions become the "master pinion" when smaller or larger diameter test rods are grabbed.
Oh well, it was a nice theory anyway...and I still paint a witness mark on the chuck and what's in it if I have to remove and replace the workpiece.
Jeff
Right you are. Some how I got off track and was thinking about a lathe chuck.
On the day of Thu, 02 Mar 2006 04:02:06 GMT... snipped-for-privacy@yahoo.com (Devonshire) typed these letters:
I forgot to mention... the chuck on this delta drill was a "ball bearing Jacobs chuck"
Devonshire
Simple. Due to inherent clearances of components, the outer member is skewed by the tightening force, so you benefit by tightening each of the positions, offsetting the deflection, with a result of a tighter grip. You usually gain better concentricity in the bargain. If the device was perfect, with no slop, and no friction, that likely wouldn't be true
Harold
Right. Makes perfect sense. I tested it last night on my drillpress and a fairly tight Jacobs chuck, seemed to behave as expected. If I was going to engineer something to check the torque at which it spins, well, then I wouldn't be making stuff. I'm sure someone has done that already.
Those of us that work with soft jaws are well acquainted with that. Using anything but the same socket when tightening the chuck will generally cost you the .0005" concentricity that is almost guaranteed with soft jaws that are properly machined. Truth is, with soft jaws, it makes no difference which socket is selected, so long as the same one is used at all times with the particular setup.
Some three jaws have a single line next to the "best" socket. Others have nothing, and some have but one socket.
Harold
That's not necessarily true. You'll find that any scroll type chuck will benefit from tightening each of the holes, but with a three jaw with which you are seeking concentricity, the socket selected will have a profound affect on how the chuck grips. The scroll has clearance on the bushing upon which it mounts, so it moves side to side with each socket. You can see that for yourself if you work with soft jaws, or you can chuck a ground piece of material that is straight and round. Each socket will provide different results almost without fail.
Harold
Yep! That's the voice of experience.
Harold
Different chucks, same problems, however.
Harold
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