Chuck precision problems

[panofish]

I am having a tough time finding a way to get good accuracy for my hollow chisel mortiser.
It has a B16 plain bearing chuck... which is showing inconsistency when I chuck the drill bit for the hollow mortise chisel. Sometimes it chucks the bit ok... other times the bit is chuck way off center and the bit wobbles badly. I would like to avoid the trial and error approach to getting the bit well centered into the chuck.

I have looked and it is very difficult to find a B16 ball bearing keyed chuck in the USA. They are somewhat common in Europe, but difficult or very expensive to purchase.

Any suggestions? I have even contemplated the crazy idea of seeing if there is a way to mount a collet fixture onto the B16 tapered shaft from the motor, since my bits are the same size shaft.
I realize that a hollow chisel mortiser is not a milling machine, but I need better accuracy for this chuck.

What do you guys recommend I try, so that I can get consistent centering of my drill bits in the mortiser?

 

[panofish]

Ok... I did a test and here are my results.
I tightened the chuck in each key hole in succession after opening the chuck several spins, removing the rod...then replacing it and tightening again.

keyhole# runout
1 .006
1 .004
1 .013
2 .014
2 .013
2 .011
3 .004
3 .016
3 .007

I then tried the same test on my drill press which has a keyless precision chuck (craftsman) and it repeatedly got the exact same .007 runout.

I then tried the same test on my milling machine with keyed chuck (Harbor Freight Mini Mill) and it repeatedly got the exact same .005 runout.

I used the same rod from a center punch kit (Harbor Freight), so the rod may actually account for .005 runout or so.

The conclusion... the cheap chuck that came with my mortiser provides inconsistent results, with about 1 in 3 chance of accidently chucking the bit on center. This might not be so bad if not for the fact that chucking a hollow chisel mortiser takes a bit more time than just chucking a bit.

Any more ideas are welcome.

 

[Wizard69]

Well drill chucks aren't perfect but that appears to be pretty bad. It might help to have a test arbor you have more confidence in. A dowel pin, a piece of drill rod or something similar would reduce the amount of wonder about your test arbor.

Considering it varies so much between runs I'm leaning towards the chuck as the issue. However have you checked the bearings in the spindle and more so the run out on the taper the chuck sits on! I could see where really bad bearings could cause some of your issues or just loose bearings.

Also on some drill presses the quits can be very loose impacting reading if you aren't measuring relative to the quil. I know this is a mortising machine but the concept is similar.

I'm not familiar with the B16 so I don't know if it is possible but you could consider pulling the spindle and having a new taper cut on it for a Jacobs style chuck. That is if the taper is any different than the common Jacobs tapers. I just looked up tapers in my Machinery's Handbook and there is no mention of B16. At least I couldn't find anything and they have a lot of tapers mentioned.

Here is a reference to some information on the "B" tapers: http://www.tools-n-gizmos.com/specs/Tapers.html. If correct you could switch to a Jacobs #2 or maybe a Jacobs #33 by machining the taper. The 33 only if there is a bit of extra meat there.

You could try ordering a B16 supporting chuck from across the pond.