Anchoring a chuck on a threaded spindle.

sicero · Sep 4, 2009

I have a South Bend 14.5 with a threaded spindle and I want to be able to operate it in reverse without a danger of coming unthreaded. I will have one dedicated chuck for this machine. It's a four jaw scroll with individual jaw adjustments also. I have no reason to change it that I can think of. I was thinking of screwing the back plate on the spindle and then screwing a lock nut tight against it and then mounting the chuck. I could run a set screw thru the lock nut into the spindle or the back plate but I doubt it would be needed. What do you think? Kenny

Ferrous Antiquos · Sep 4, 2009

With only 8-tpi it wont take long for the chuck to come off the spindle should things go awry. But, at least it will roll away and not into your lap.

I guess you'll have to make a custom spindle adapter that allows room for the locknut idea.
If you secure it with one or two setscrews and make little brass inserts, I have a 2.25-8 tap that I could chase them out for you.

Peter from Holland · Sep 4, 2009

Make a split ring with a bolt through the split part and put itover the smaller OD of the backplate and bolt it tight

That way you shrinkfit the backplate on the cilindrical part behind the thread on the spindle
That is the way Schaublin does it

Peter from Holland

Jackmo · Sep 4, 2009

What I did was to drill & tap 2 or 3 holes perpendicular to the threads & insert set screws with either brass or nylon tips. You don't have to really crank on the set screw just snug is all it will take.

Jackmo

Mark Rand · Sep 4, 2009

Just spin the chuck firmly onto the mandrel and the use it. Be gentle when working in reverse and the chuck will stay on. It has worked for several generations of South Bend, Boxford and Myford owners

Removal can take a bit of effort.

moonlight machine · Sep 4, 2009

put it in back gear to lock the spindle. Screw it on to 1/4 turn from tight give it a quick firm spin to tighten it up. It will stay on if you don't get too crazy. I'v run mine in reverse lots of times with no problem.

sicero · Sep 4, 2009

I have run my 10 L in reverse many times also. I have also had it come loose at the most inoportune time. It's a little like wearing the seat belt in my truck. I don't know why I put it on, I have never needed it. I think I will just bore the back plate enough to get a lock nut on it. Ferrous Antiquos, Thanks for the offer of the tap. These threads are 2&1/4" X 6tpi. I don't have any problem cutting threads. Kenny

Peter from Holland · Sep 5, 2009

The solution I offered is the only one IMHO which prevends the chuck from getting more runout
It is also easy to make and clamps real tight
Tighter as a setscrew
I made some pics from an old backplate I had lying around to clearify it

Peter from Holland

Willy · Sep 5, 2009

This approach works well too if you have the room to implement it.

Screwmachine · Sep 5, 2009

The Schaublin ring Peter shows does work surprisingly well. I've seen it abused on lathes equipped with brake/clutches and never a launch.

Charles_nl · Sep 5, 2009

Maybe for a Schaublin, where everything is measured in 0.01 of millimeters, but a South Bend ain't no Schaublin. If the fitting of the chuck is not very precise with the cylindrical part of the spindle, the method may be unsafe.

I did a quick measurement on my Logan (a better South Bend:-): the cylindrical part of the spindle is (with calipers) between 37.98 and 38.01, while the internal diameter of the mating part of the chuck is about 38.83 on one, and 38.43 on the other chuck. The rim on the chuck is ~11mm thick and I don't think you would be able to squeeze that rim 0.8mm to get the tight fit. And how would you check?

Regards, Charles

bytewise · Sep 5, 2009

clamp ring

In order for the squeeze clamp to work I think you would need to slit the hub in 3 or 4 places like a collet.
Hugh

Charles_nl · Sep 5, 2009

Yes, that might be a solution, did not think about that. But the picture of Peterve did not show such slits and it still works, he says: the fit must be much better than on my Logan (and SB).

Charles

Peter from Holland · Sep 5, 2009

Charles_nl said:
Maybe for a Schaublin, where everything is measured in 0.01 of millimeters, but a South Bend ain't no Schaublin. If the fitting of the chuck is not very precise with the cylindrical part of the spindle, the method may be unsafe.

I did a quick measurement on my Logan (a better South Bend:-): the cylindrical part of the spindle is (with calipers) between 37.98 and 38.01, while the internal diameter of the mating part of the chuck is about 38.83 on one, and 38.43 on the other chuck. The rim on the chuck is ~11mm thick and I don't think you would be able to squeeze that rim 0.8mm to get the tight fit. And how would you check?

Regards, Charles

If it needs to rim 0.8m you first worry would be to make a new backplate :nutter:

That is the part were it needs to fit, not on the tread That can be a rather loose fit
If south bend did provide these parts with that fit you better look for a chinese machine Much better probably

That 11mm OD rim is easy to reduce to 7 or 8 mm or so
And even with a 11mm rim I don`t think it is a problem squeezing that 0,02 to 0,04 mm and that presents a very loose fit on your shaft/backplate . 0,01 would be right I think Perhaps tighter on a Schaublin
Also no need to sleeve it IMHO

This is not something I have invented
It is a general design seen on other lathes too beside Schaublin
Can you also say that for the lock screw in the side on the threads??

Peter from Holland

Troup · Sep 6, 2009

moonlight machine said:
.... I'v run mine in reverse lots of times with no problem.

Me too - in fact in 35 years I never had a chuck unscrew on my Myford.

Then I had it happen twice in two months: Reason: I'd fitted a larger motor pulley, and the direct-on-line starting in reverse was suddenly too aggressive

It's no fun catching a spinning chuck, although admittedly hands heal quicker than lathe bedways ...

Thanks a LOT peterve for the Schaublin approach. My backplate registers fit so closely I had one jam the other day with a piece of airborne grit (also first time in memory - I'm usually pretty fussy about cleaning the register, but I recently downgraded one of my Myfords for toolpost grinding, getting through skin on small castings etc... and I got a bit slapdash)

So I'm going to give this method a try: it's the first I've seen which I feel is a really good bet.

I would agree that a backplate which doesn't fit well enough for this idea to work should be replaced, unless it's a 'utility grade' lathe

Charles_nl · Sep 6, 2009

OK, I don't expect my Logan to be a Schaublin, so I will keep it.

Unfortunately, I did also a quick check on my old Kärger "precision plain-turning and screwcutting lathes" (Tony's description), and I have to throw that lathe away! The register measures 26.74, and all but one of the accessories that came with the lathe (3-jaw, 4-jaw, 2 2-jaws, 2 face plates, the internal and external step chuck holders, and a couple more) measure around 27.30. Gone is the precision, a pity! But maybe an excuse to buy a Schaublin, finally:-)

But I think Peterve's method is very nice, when it works: no damage is done.

Charles

Peter from Holland · Sep 6, 2009

Charles_nl said:
But I think Peterve's method is very nice, when it works: no damage is done.

Charles

It works no doubt about that if the fit on the register is within specs
In your case perhaps you can sleeve the backplates
It would surely improve repeatability

So we can learn from all this to check the fit of the register from the backplate on a threaded spindle if we have runout on the chuck

Peter from Holland

Jim S. · Sep 6, 2009

I can confirm that Peterve's suggestion works. I recently made up and threaded a backplate to fit my Schaublin 102. Even though I did not get a precise fit between the inside bore of the backplate and the unthreaded portion of the spindle, I build a clamp ring along the lines of the original Schaublin design. I was a bit skeptical that the ring would clamp the backplate sufficiently to prevent turning but I tried it and am pleased. I have no way to really measure the force it would take to overcome the clamp but the few times I have forgotten to loosen the clamp I certainly could not get the chuck off......

Overall, it works fine......prevents the chuck from unscrewing and the chuck mounting is repeatable to within my capacity to measure.

Jim

Anchoring a chuck on a threaded spindle.

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