Refreshing a drill chuck.

[Highpower]

What to do...... what to do?   

It looks like my old Jacobs 14N drill chuck had spun on its arbor about 180° at some point, and scarred up the very top of the taper inside the chuck. Getting another arbor is easy. But how do you go about cleaning up the taper in the chuck body? Counter bore the end slightly? Try grinding off the high spots along the damage line? 

   


   

And the offending MT3 - JT3 arbor with the rolled up lump.


   

[f350ca]

I'd try grinding the offending spot with a small stone in the Dremel.
Opportune time to post this.
My keyless chuck loves to come loose on the low cost R8 arbour I bought, no scars YET. Why couldn't I warm the chuck in the oven to say 2 or 300 F and instal the spindle. I know you shouldn't have to BUT.

[dallen]

freeze the arbor then use a hunk of 2X4 to drive them together

[f350ca]

(04-29-2015, 08:56 PM)dallen Wrote: freeze the arbor then use a hunk of 2X4 to drive them together

Should have asked in January.

[Vinny]

Is there a JT3 reamer available anywhere?

[Highpower]

Yes, but they are a rare bird and priced accordingly.... 

[TomG]

I've chucked those up and stoned the tapered bore before. If you use a round stone and a little care, you can remove the galling without screwing up the taper.

Tom

[dallen]

(04-29-2015, 09:17 PM)f350ca Wrote:

(04-29-2015, 08:56 PM)dallen Wrote: freeze the arbor then use a hunk of 2X4 to drive them together

Should have asked in January.

August around here you put the chuck body outside and give it a couple hours then knock in the arbor with a rawhide mallet.



da

[Dr Stan]

I'd consider using Loctite at assembly. Just remember you'll probably never ever get it apart again. Epoxy would also be a possibility. At least one can soften it by heating with a hot air gun or low temp oven.

[Roadracer_Al]

I'd avoid any chemical adhesive. I'd definitely avoid the dremmel as it will remove too much material quickly.

Consider that when they were new, the surfaces were close to the geometric ideal cone. However... there was a little bit of grit that got between the male & female sides of the taper, preventing it's ability to wring together, reducing it's torque capacity, so it spun. That little bit of grit then acted like a plough in a field.

Basically, a dent, ding, burr or other deformation has two components -- a low spot and a high spot, just like a furrow in a field. We can easily remove the high spot so it comes back down close to the geometric ideal cone. We don't need to remove the remaining low spot, it just doesn't matter.

Clean both halves with acetone and a lint-free rag, then use a sharpie -- or prussian blue, if you have it -- to determine the fit. Cover the entire male side of the taper with sharpie and wring the taper together. If, after you separate them, you see shiny spots on the male side, they're high. If you see dark spots where the sharpie has transferred to the female side, they're high. High spots get taken down with a stone.

Tom's right -- use a fine round stone to tidy up the female side of the taper, and a fine flat stone to tidy up the male side. I'd do it by hand and not under power, it's easy to make it out-of-round.

When you are rubbing the high spot with the stone, you will notice that the shiny bit "spreads" as the high spot is removed. It's becoming closer to the ideal cone. Don't remove too much or you'll make a low spot. Low spots do not contribute to carrying torque. You really want to sneak up on the good fit with lots of testing iterations.

Clean both halves with acetone and a lint-free rag and re-apply the sharpie to test again. When it looks mottled uniformly, it's a good fit.

Then, clean both halves with acetone and a lint-free rag again (noticing a theme?) and assemble. Retract the chuck jaws and seat the taper with a single sharp blow with a rubber mallet.