SB 9A lathe chuck size

I am going to replace the 3 jaw chuck on my SB 9A and I am considering a 5" verses a 6". It seems that a 6" chuck would allow greater flexibility in terms of holding larger diameters. However the 6" also weighs more and has greater swing weight and start up momentum. What other arguments exist against the 6" size? I know that the Jaw protrusion is limited to about 1.5" from the chuck body on the 6" before it might contact the carriage. The 5" chuck would theoretically hold a larger piece (4")than the 6" (3") without reversing the jaws.

Also does anyone know of problems with the fit of a prethreaded 1 1/2 X 8 backplate (Bison) on the 9A lathe? I read that the best way to mount a new chuck is to buy a blank plate and custom thread it to my lathe spindle. Seems reasonable and a lot more work.

Any thoughts on these topics are appreciated.

Thanks,

Dan

I have an 8" Atlas four jaw chuck on mine and it has alowed me to do some things that a 5" or 6" would never have. The 8" has not been a handicap in any way. Gary P. Hansen

I also have an Atlas 8" 4 jaw on my 10K and it comes in handy. I have 5 chucks and its hard to pick a favorite because i use them all. I have bought 2 prethreaded back plates and they are fine...Bob

I had bad luck with a prethreaded backplate, and it was a Bison. Probably just an anomaly, as others have had good luck -

Blob

Thanks for the input...is an Atlas chuck in current production and if so who sells them? Does anyone have a 6" or larger 3 jaw scroll chuck on a 9A?

i just put a six jaw chuck that i got from tools for cheap on my 9A tonight. it came with the back plate. first thing i chucked up was a cut off peace of a crank shaft and only had .0015 runout

DO read Paula's thread on fitting a threaded back plate for minimum overhanging weight.

A current 6" chuck is actually 6-1/4" and is really, really heavy compared to the older true 6" chucks.

I used Paula's technique when adapting a chuck to a Gulledge dividing head, and I was very pleased with the result.

The head's spindle projects about 3/16" into the chuck's pinion retainer.

Here is the Atlas link...Bob
http://www.prattburnerd.com/products2004/products_self-cent_frame.htm

Paula's method for minimizing overhanging weight is found Here.

Excellent work Paula, I'm going to do the same process in mounting the new 6" chuck. Thanks to all for the prompt response to my questions...this forum is great! It saves so much time and wasted effort in getting things right.

Gary, I now have an 8" 4 jaw chuck and was reviewing Paula's procedure for minimum overhang. The problem is that it looks like I'll have to machine a 45 degree chamfer on 1/2 the thickness of the adapter plate edge (on the headstock side) in order to clear the "toe" of the headstock. Has anyone else done this?

chippindan: I do not know. My Atlas chuck does not have a back plate. The chuck it self is threaded. Gary P. Hansen

Dan,

What is this "toe" you are referring to? Most of the 9A headstocks I've seen are clear in the corner between the headstock and ways, as shown in this cross-section:



I once fitted an 8" 3-jaw chuck to my 10K. I have to say, in retrospect, that it was mostly a waste of time. It was more spindle weight than the drive could adequately handle. I would have to engage the belt slowly, with the motor running. Otherwise, the flat belt would just slip off the spindle cone pulley when the motor was started. Then it took a looong time to coast to a stop once the motor was shut off. Plus, it was a PITA to install and remove the thing, due to its weight. You also need to remember that a larger chuck also has larger jaws, particularly in the lathe swing direction, so you can't really use the chuck to anywhere near its capacity on a 9 or 10" lathe.

Now, a faceplate is a different matter -- get the largest that will fit on the lathe.

Paula

FYI,

The later model 9Á's did indeed have a toe at the front of the headstock.

See picture.

Regards,

Piet

Piet, your pic is not very well lighted but I can see a toe as you call it under the chuck. I have seen a lot of SB 9s and a few 10Ks over the last 60 years, but have never seen one with a toe. The Heavy Tens I have seen and mine do have toes. I made a mistake buying a 10"dia. -2-1/4" -8 Thd. face for my Heavy Ten and found the toe would not let me screw it on fully.
My main chuck on my 9A is a very heavy 6-1/2" that I was able to partly bury the thread nose into to keep the overhang low.
I have a new 8" chuck with 2 piece jaws I am fitting with minium overhang to my Heavy Ten.
Walt

Hmmm, interesting... That's a new one on me too.



Paula

Walter / Paula,


did some scrolling thu 'the' lathes.co.uk pages in the SB Section and the 'toe' seems to be common on all the underdrive types. Maybe it has to do with improving the ridgity of the headstock because of the underdrive design requiring rather large openings in the bottom of the casting.

Regards,

Piet

The picture with the toe is an underdrive machine. As far as I know all under drive 9's and 10k's used that style of headstock casting.


Joel

Piet,

That seems like a reasonable explanation. I wonder why I never noticed the "toe" before. It looks as though SB re-designed the underdrive headstock by the time the 10K appeared, such that the toe was no longer needed, as it appears to be "toeless".

Paula

CORRECTION: Looking into this further, it seems that some of the 10Ks (the earlier ones?) had the toe, and some did not. I know that the late-model 10K I owned was toeless.

Paula,

the 10K had one inch more 'beef' at the underdside, believe the slot is still the same.

But the 1" extra probably did it.

Walter,

sorry fo the poor photo quality it was taken with a video cam.

The lathe is sold though, as it was just too much to tool here up for a decent amount of money.

Shouln't probably mention this in this forum but I've bought a loaded Myford ML-7 with all the usefull accessories such a swivelling mill slide & vice, original dividing head, saw table??, 4 jaw, face plate, drive plate et. Althoug the QCB and power X-feed are sadly missed. I, would have liked to held on to the SB but the addtional cost required to have it fuly equipped was just too much. It also got me a bit nervous from time to time with the clackin belt and resonating motor cabinet.

Big plus for all the rear drive owners is that U can fit a seemles serpentine belts on your machine that probably makes it run whispering quiet.


The pleasant surprise of the Myford was the noise, or lack of it. And a good second one was the luxury of a spindle clutch.

The ML-7 and acc. are all stripped to the very bare bone for cleaning, inspection and painting plus it will be my first project in grinding scraping as I want this lathe to be as square as new.

So far I hav had lot's of help, tips & tricks from very experienced people so I am confident about the end result.

So even though I'm no longer a SB owner I take the occaisional stroll thru this forum.


Hope you 'guys' don't mind. And aopologies for going way off topic here.

I wish there was such a good forum within PM on Myford lathes.

Just noticed there is a rear drive 9A on one of the Dutch ad pages. You'll never know...


regards,

Piet