[ecope]

Hello. I have a 1/2" Jacobs Drill Chuck that I have had for nearly ten years sitting on my tool box and decided to make a arbor for it and use it on my taig CNC mill. The first thing I noticed was the drill bit was out of round when the chuck was spinning. I think the reason was one of the jaws when closed together was a little longer than the other two therefore causing the drill bit to wobble. It being an old chuck (although never been used) I thought I would buy another one, so I found another 1/2" Jacobs Drill Chuck at my local Harbor Freight. So I purchased it for about $10.00 and one of its jaws are a little longer than the other two.

So it there anyway to correct this problem or should I buy a different brand at a higher price?

Thanks,

Eric

[Jigantor]

Are you sure it is not the arbor?

Ji

[victorofga]

how did you check taper angles? did you check with indicator , or simply tried as long as it was fit?

on net you can find exact angles for morse taper and for JT jacobs taper..
of these angles you can figure for a given length how much they are descending..

making out them this way you have a good chance that first try successful..

also question, how did you made tapers? between centers both, or after morsetaper was ready simply put into lathe spindle?


in worst scenario, you can turn a ""shaft"" and tie onto the chuck with a blank.. and after cnterdrilling you can turn the morsetaper..

[ecope]

I should have also said that the mount for the chuck is for a 1/2"-20 thread. The arbor I made was from a 1/2"-20 all-thread rod and I just turned down one side to 3/8" to fit my ER collet on the machine. So I don't think it would be the arbor out of round but I will check with a indicator to make sure what the runout is.

Also, the way that I checked the jaws was just screwed the chuck until the 3 jaws was touching and that is how I noticed that the one was longer than the other two. I pushed on the longer one to see if it had some play in it but it was just as tight as the other two.

So I am thinking that the longer jaw is causing the drill bit to be pushed out some to cause the wobble.

Thanks for any more solutions.

[victorofga]

well... you can try many way..
for threaded chucks beyond thread need a shoulder..
a rolled thread i think will not work..
at least very little chance for runout..

your only way to tigth a piece of that threaded rod into chuck back, tie a 1/2-20 nut onto, to lock the threaded shaft and put the chuck onto a 1/2 inches diameter in the lathe.. and carefully make out the 3/8 or any diameter to fit into your taig mill..

however any time the nut loosing up youll loose the runout again with the chuck..

certain way you can ignore it.. and try any other way...

also, if that chuck is bad, you can buy another one..

1/2" MT2 Mini-Lathe Drill Chuck

this chuck has jacobs taper in the chuck.. i have this for my lathe and mine is run nicely..

[Mrdrillchuck]

Jacobs us made in China, specially those cheap chucks like at Harbors tools.. You get what you paid for more less.. The jaws on the chuck must form a even point when closed completely, if not the drill chuck will not be held straight.. Purchase a chuck made in France or Germany.. LFA or Rohm are now leading brands for quality in the USA..