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View Full Version : Atlas 6 inch 4 jaw independent 1 1/2 x 8tpi chuck problem



JMJM
03-09-2015, 09:35 AM
When I bought my used 9 inch South Bend around 1980, it came with a Cushman 5" 3 jaw and an Atlas 6 inch independent 4 jaw. The Atlas doesn't seat up to the shoulder on the spindle but acts more like snugging up a pipe thread and get within about 1/4 inch of the the shoulder.
No problems truing up the work in the chuck or during turning but seems it ought to seat fully. The Atlas model is 10-864B. The internal threads on the chuck are clean with no visible nicks or damage.
Any thoughts?
JMJM

George Seal
03-09-2015, 11:05 AM
If it were me I would turn a spacer that fit between chuck & spindle

JCHannum
03-09-2015, 12:44 PM
There are three possible causes for this. To diagnose, remove the backing plate from the four jaw and install it on the lathe spindle to see how it threads on.

One is that the register in the four jaw is different than that of the Southbend. This is the recessed area at the rear of the mounting area of the chuck where the threads are relieved. Check diameter and depth compared to the three jaw and modify the four jaw mount to match.

The second is the ID of the mount is undersize compared to the Southbend. The solution is to chase the threads deeper.

The third possibility is that the backplate is too shallow and the spindle is bottoming on the chuck body. In this case, a spacer is the solution.

The first two are more than likely the cause as spindle and thread dimensions did differ slightly among the various manufacturers and the fitup can be tight or loose as a result.

lynnl
03-09-2015, 12:47 PM
......and an Atlas 6 inch independent 4 jaw. The Atlas doesn't seat up to the shoulder on the spindle but acts more like snugging up a pipe thread and get within about 1/4 inch of the the shoulder.
No problems truing up the work in the chuck or during turning but seems it ought to seat fully. ..........
JMJM

What is your experience in removing that chuck after a job is complete? Is it hard to remove?

If it's not seating against some hard surface I'd think it would screw on tighter until becoming almost impossible to loosen.
What I'm hinting at, is maybe it's actually seating against the end of the spindle itself. ...just guessing.

(added) I see JCH's 3rd possibility already covered that.

Rich Carlstedt
03-09-2015, 01:47 PM
There are three possible causes for this. To diagnose, remove the backing plate from the four jaw and install it on the lathe spindle to see how it threads on.

One is that the register in the four jaw is different than that of the Southbend. This is the recessed area at the rear of the mounting area of the chuck where the threads are relieved. Check diameter and depth compared to the three jaw and modify the four jaw mount to match.

The second is the ID of the mount is undersize compared to the Southbend. The solution is to chase the threads deeper.

The third possibility is that the backplate is too shallow and the spindle is bottoming on the chuck body. In this case, a spacer is the solution.

The first two are more than likely the cause as spindle and thread dimensions did differ slightly among the various manufacturers and the fitup can be tight or loose as a result.

A big +1 for Jim

Most likely the bore in the plate is smaller than the shoulder...door number 1
Rich

lakeside53
03-09-2015, 01:47 PM
It needs to screw onto until it his the vertical register (after the shoulder). Don't just bind it into the threads.

Follow JC post above...

Andrew S. Quinn
03-09-2015, 08:24 PM
I have a 9" South Bend,and an Atlas 4 jaw,and it does the same thing...

J Tiers
03-09-2015, 10:05 PM
What you could be running into is the difference between sharp threads and standard ones with the truncation at major and minor diameter.

South bend stuff uses the standard thread, and does not fit Logan (or maybe Atlas) without the threads being scraped-out a bit to clear the area where the full-V thread goes. Same may be true of the chuck thread on the spindle, in which case grinding a bit off the points of the chuck internal threads is in order.

The two can screw together farther than it would seem they should before they bind up. Maybe that's from wear, I don't know. My S-B dog driver plate stopped about 0.25" from the shoulder of the Logan spindle.... a bit of scraping out of the thread tip area in the drive plate fixed it.

JMJM
03-10-2015, 11:48 AM
It needs to screw onto until it his the vertical register (after the shoulder). Don't just bind it into the threads.

Follow JC post above...

Good to know I'm not the only one ....

JMJM
03-10-2015, 11:53 AM
What you could be running into is the difference between sharp threads and standard ones with the truncation at major and minor diameter.

South bend stuff uses the standard thread, and does not fit Logan (or maybe Atlas) without the threads being scraped-out a bit to clear the area where the full-V thread goes. Same may be true of the chuck thread on the spindle, in which case grinding a bit off the points of the chuck internal threads is in order.

The two can screw together farther than it would seem they should before they bind up. Maybe that's from wear, I don't know. My S-B dog driver plate stopped about 0.25" from the shoulder of the Logan spindle.... a bit of scraping out of the thread tip area in the drive plate fixed it.

Interesting observation, I'll have to check that out. Should be able to mike that difference. May decide to take George Seal's suggestion re a spacer ring. Never had any more trouble removing the 4 jaw than my 3 jaw Cushman but never had the 4 jaw on for long periods of time or heavy turning operations. Thanks to all.
JMJM

Ironwoodsmith
03-10-2015, 03:09 PM
I bought a nice 10" faceplate on Ebay for my 11x36 Logan and had the same problem. Mine is 8 tpi by 2.25". I ended up chucking it up and rethreading until it would snug up to the collar. Then I faced it true. It was a good exercise for me with my new lathe.