Thread: Jacobs chuck / Sawtooth bit adventure: Tool or technique?

Put it back together with a little persuasion when inserting the JT taper at the chuck base. You should be able to retract the bit from the piece of wood by turning the piece in reverse by hand while holding the drill chuck steady. After the chuck is removed from the wood piece, make sure the JT taper end is inserted snug into the drill chuck, use a good solid mallet or a hammer and hit the Morse taper end to fully seat the JT end into the drill chuck. That will help tremendously. ................. Jerry (in Tucson)USA

Originally Posted by Nubsnstubs

Put it back together with a little persuasion when inserting the JT taper at the chuck base. You should be able to retract the bit from the piece of wood by turning the piece in reverse by hand while holding the drill chuck steady. After the chuck is removed from the wood piece, make sure the JT taper end is inserted snug into the drill chuck, use a good solid mallet or a hammer and hit the Morse taper end to fully seat the JT end into the drill chuck. That will help tremendously. ................. Jerry (in Tucson)USA

Thanks Jerry

I managed to remove the bit, as you suggested but my MT / Jacobs problems compounded, and the arbor locked-in to the tailstock and could not be removed.

Being new to this equipment I was reticent to apply a lot of force either via the wheel or a knock-out bar, fearful of messing with the bearings or other components of the tail stock. Luckily we have a freindly 'machinery specialist' engineer professional in the area who helps hobbyists gratis or for a pack of beer. He visited, showed me how to stabilise and lock everything up so that higher force levels could be applied without risk of damage, and hit the knock-out rod a lot harder than I was willing to. The arbor is removed, and he showed me the fine damage to its surface.

So now, upon his advice, I am applying 1200 grit to the surface to remove the fine gnarling.

Once that is done I will, as you suggest, apply a little more force to join the arbor and the chuck head. Thank you very much. Fingers crossed

I have a chuck that would often do this. The last time it did it I sat the chuck on top of my gas patio heater for 10 minutes prior to giving it a solid tap in, it's never come off again.
It's important that both surfaces are dry and clean before assembly and do retract the jaws prior to a solid tap together.

The issue you are having is very common. Morse tapers are designed to hold firmly under compression and not under tension, which is happening when you are retracting that 2.5" bit.

What you are using is a standard arrangement, but at that drill size (I presume a Forstner bit) you need an adaptation... the addition of a draw bar to hold the MT in place while withdrawing the bit.

Jacobs chuck with drawbar.jpg

If the end of the MT is not already tapped, it needs to be drilled and tapped. That is not difficult, even I have managed to add an 8mm threaded rod to some of mine.

The above photo is for use in headstock where it can safely hold unsupported small pieces. Note: smaller locking nuts are needed for use in the tailstock.

Go lightly with driving the MT home. A firm thrust by hand is usually sufficient. Regrinding and reaming can clean up any light scoring, but if overdone can reduce holding capacity.

Good advise Neil but in this case it can't help as it's the Jacobs taper that's releasing, leaving the Morse taper in the spindle.

Brilliant, thanks.

Yes, I am using sawtooth style 'forstner' bits p to 3.5".

What you explain makes a lot of sense.

The end of my chuck arbor has a tang. It is not tapped, only having a small (3mm diameter) central hole about 1mm deep. I don't have the ability to change that but my woodworking club has a metal working arm, with such expertise and equipment. Once we're thru Christmas, and open again, I will ask one of them to tap that end for me.

That approach will help retain the chuck arbour in the tailstock quill during withdrawal, but the arbor can still separate from the chuck head can't it? I don't know that drilling the full length of the arbor, and into the base of the chuck head itself, is viable. I wonder if (shudder) loktite might be useful on that end of the arbor.

Originally Posted by Picko

Good advise Neil but in this case it can't help as it's the Jacobs taper that's releasing, leaving the Morse taper in the spindle.

Snap. Yeah, I just posted much the same.

Neil's advice does seem to cover one aspect of the problem though, and helps me appreciate that this is not an isolated problem ... which is always good to learn

Let me try paraphrase so I understand clearly.

You're talking about expanding the chuck head aperture a little with heating and thereby allowing the arbor to seat home a fraction of a mm further. Then when the chuck head cools the arbor is much more tightly gripped and less likely to separate.

Is that right? If so, that sounds like an awesome suggestion ... and something I can do myself.

That's it, exacary.

Originally Posted by DXW

...the arbor can still separate from the chuck head can't it? I don't know that drilling the full length of the arbor, and into the base of the chuck head itself, is viable. I wonder if (shudder) loktite might be useful on that end of the arbor.

OK, was in a bit of a rush.... should have read your original post more carefully. So, Jacobs chuck end is the problem.

No, drilling and tapping all the way through to Jacobs chuck is overkill.

Loctite or similar is what is used with press fittings, so should help keep Jacobs chuck and arbor together. Clean the mating surfaces as specified by product and after application keep under compression by winding tailstock with with MT/arbor/chuck up against a piece of wood in headstock for required time for CA glue to set.

And, of course, avoid getting any CA on the MT end....

Edit: Try Picko's method first and if that doesn't work for you then have a go with the CA.

I've had two chucks that used a small screw from INSIDE the chuck to "bolt" it onto the MT.

Retract the fingers right back and look inside. It wasnt much of a screw, just a little M3 with an Allen key head. Did up in reverse as well, I think

Didnt really think about it until now, but its obviously there to stop the withdrawing problem and having the chuck pop off!

My standard technique for fitting a taper arbor to a taper chuck is to freeze the arbor in a freezer for at least a couple of hours if in physical contact with the freezer liner, or somewhat longer if on a rack or shelf, gently heat the chuck body with a heat gun or similar (not direct heat with a torch or similar), bring them together with leather gloved hands and give one end of the setup a moderate tap with a rubber or leather mallet. Of course you want the chuck jaws fully retracted for this so the mallet impact does not transfer from the jaws to the feed mechanism of the chuck.

Freezing the arbor shrinks it, just as heating the chuck body expands it. The moderate tap sets the arbor deeper into the chuck recess, and the whole lot normalises to room temperature over a couple of minutes to form a very secure attachment.

Originally Posted by woodPixel

I've had two chucks that used a small screw from INSIDE the chuck to "bolt" it onto the MT.

Retract the fingers right back and look inside. It wasnt much of a screw, just a little M3 with an Allen key head. Did up in reverse as well, I think

Didnt really think about it until now, but its obviously there to stop the withdrawing problem and having the chuck pop off!

Portable electric drills typically have a male threaded output shaft with an opposite handed female thread through the centre and a chuck with a female thread matching the male thread on the shaft, and use a reverse thread screw to sandwich the chuck body between shaft and screw as a secondary method to secure the chuck, so chuck cannot unscrew from shaft regardless of direction of rotation.

I haven't seen this done much for arbor mounted chucks, but I'm sure that arbors set up for this would be around to accommodate that style of chuck.

Malb, I'm certain you are correct on this.

I looked through my purchase history and even tried to find one in Google images, but could not.

I must have been remembering my drills.

I'm getting fuzzy!