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New Chuck Backing Plate runout.

Denny Graham

Aluminum
Joined
Sep 1, 2004
Location
Sandwich, IL
So I've been working with my old Logan 825 10" lathe with the
6" 3-jaw chuck that it had on it when I picket it up 30 years ago.
I broke down this week and bought a new 3-jaw and 4-jaw for it.
I was getting ready to fit the "Fully Machined Threaded Backing Plates"
up to the plane back chucks and when I checked the plates for run out
and found they both, (one for each chuck) run out .009"-.010".
The nose of the Logan lathe spindle is on size i.e., 1.4985" but
the boss in the back of he adapter plates is already bored out
to 1.515"-1.516"
I'm kind of stuck as to what to do. I can mount up the backing
plate and turn it to fit it's new chuck but I'm afraid it's not
going to repeat when I change chucks if it's locating on the
thread only.
Any ideas????
Shars Chuck Backing Plate Runout photo - dennygraham photos at pbase.com
Shars Chuck Backing Plate Runout photo - dennygraham photos at pbase.com
Thanks,
Denny Graham
Sandwich,IL
 
So I've been working with my old Logan 825 10" lathe with the
6" 3-jaw chuck that it had on it when I picket it up 30 years ago.
I broke down this week and bought a new 3-jaw and 4-jaw for it.
I was getting ready to fit the "Fully Machined Threaded Backing Plates"
up to the plane back chucks and when I checked the plates for run out
and found they both, (one for each chuck) run out .009"-.010".
The nose of the Logan lathe spindle is on size i.e., 1.4985" but
the boss in the back of he adapter plates is already bored out
to 1.515"-1.516"
I'm kind of stuck as to what to do. I can mount up the backing
plate and turn it to fit it's new chuck but I'm afraid it's not
going to repeat when I change chucks if it's locating on the
thread only.
Any ideas????
Shars Chuck Backing Plate Runout photo - dennygraham photos at pbase.com
Shars Chuck Backing Plate Runout photo - dennygraham photos at pbase.com
Thanks,
Denny Graham
Sandwich,IL

They are nearly always like that for threaded mounts. A2, D1(X), L(X) tapers, not so much.

First several I fitted 1959-60 to a brand-new Logan and a brand-new SB 10" "toolroom" next to it included, so not a new thing or a Chinese-source era thing.

Watcha do is take a light cut first to true-up to near-as-dammit zero TIR.

THEN you can take 'em on and off several times to make sure the threads and register shoulder are repeating on THAT one spindle.

Once that works, or needed corrections are made, THEN you are safe to turn final fits for a given chuck.

I did have to chase the ID threads & register on two of the four our school had purchased. That was a Logan vs SB thing, IIRC. The shop instructor wanted full interchangeability due to budgets being tighter than training-project tolerances.
 
Threaded chucks center on the threads...the pocket doesn't matter so much...if it were too tight a small chip could be a real problem, your plates radial clearance sounds about right.

it the interaction of the threads and the spindle face that provide repeatability.
 
Ok then. I was thinking the same thing, that is, that the thread would pull the plate up
in the same place each time. Still, I worry about the clearance in the thread being a
problem.
I watched Tubalcane turning a new backing plate for, I believe it was an Atlas.
He turned a boss in the back of the plate that piloted on to the unthreaded shoulder
right behind the threads on the spindal. As I said, the boss in those cast backing
plates is already over size by about .015".
So....I guess I'll give it a try. Worst case is I'll be out $89 if I have to buy a
a new plate. Then again, I could turn a reducer and press it into the existing boss
and bore it to fit the shoulder on the spindle behind the thread.
Thanks for posting.
Denny G.
 
Ok then. I was thinking the same thing, that is, that the thread would pull the plate up
in the same place each time. Still, I worry about the clearance in the thread being a
problem.
I watched Tubalcane turning a new backing plate for, I believe it was an Atlas.
He turned a boss in the back of the plate that piloted on to the unthreaded shoulder
right behind the threads on the spindal. As I said, the boss in those cast backing
plates is already over size by about .015".
So....I guess I'll give it a try. Worst case is I'll be out $89 if I have to buy a
a new plate. Then again, I could turn a reducer and press it into the existing boss
and bore it to fit the shoulder on the spindle behind the thread.
Thanks for posting.
Denny G.

It isn't just the 89 bucks.

Take your time, doublecheck, look for vids, still photos, narrative explanation from those who have the EXACT same lathe and spindle as you have.

The "details" of that register area differ from one maker to another, even on same TPI and diameter, and you don't REALLY want to have to fit a bushing.

Hopefully that part goes well.

The other challenge you should give thought to is that smallholders are often challenged as to measuring tools and skill suited to accurately measuring the OD of the backplate (easier) AND the ID of what can be a rather shallow back recess (harder) that is meant to match to a superb fit with it.

Whatever you have planned for that operation, best to confirm that it - and you - are up to that challenge well ahead of time.
 
I was looking at this on my South Bend. Two chucks(3 jaw and 4 jaw listed below) that were factory supplied (based on the invoice from 1979, and the markings on the chucks) have significantly "oversized" registers. The register area doesn't center the chuck; the threads center the chuck as the chuck tightens on the spindle and it develops a force against the spindle shoulder.

One thing I've never seen discussed is the relationship between the face on the back of the chuck adapter that sits on the shoulder of the spindle and the axis of the threads in the backplate. If these are not truly perpendicular, I could see it causing real problems with chuck mounting accuracy. I've seen instructions that suggest that you can thread the adapter on backwards against a spacer to trim this surface, but if the face of the adapter and the back of the adapter are not parallel I think that could get you in trouble.

I think tomorrow I'm going to try bluing up the spindle shoulder and see what the prints look like on my chucks.

I've been thinking about this in the context of my collet chuck, which has only about 3 threads holding it to the spindle, and the work I'd have to do to improve this situation.

Readings on several chucks:
attachment.php
 
I've seen instructions that suggest that you can thread the adapter on backwards against a spacer to trim this surface, but if the face of the adapter and the back of the adapter are not parallel I think that could get you in trouble.
One DOES so reverse them if/as/when need be. Part of your JOB if they are found wanting is to make the surfaces parallel to each other and dead-nuts ON the plane of rotation. Not hard with SB straight threads. Some other lathes are tapered a tad.

The planar and parallel stuff? It isn't a milling machine with a nodding or tilting head. Lathes JF do that if not unduly interfered with. They don't inherently know how to do anything else!

:)
 
Thanks Monarchist? I haven’t been round here long enough to know your real name.
I realize it’s hard to know how much experience one has or his skill level when
they post to a forum like this. So…a little background. I’m not a complete novice,
not a die maker by any means, but we, the family, have had a mill and lathe in the
basement or work shop ever since I was a wee toddler. And we had a welding
fabrication/machine shop business for many years before I got out of the rat race.
I’ve worked in machine shops a large portion of my adult life and I’ll be a 76 year
old adult in a few months.
I’ve had the Logan 825 for many decades, it’s a good little lathe for a home shop,
certainly not the caliber of a Monarch or Hardinge but for the type of work I do here
at home, it fills the bill.
I just finished a limited restoration of a 1916 16” Lodge & Shipley lathe for turning
some of my larger projects. Have had my round ram Bridgeport in the home shop
for about 30 years and am in the process of refurbishing a 48” table 2HP Bridgeport
variable speed I picked up a few years back. I have a pretty good selection of tooling
and measuring tools and worked for the last 15 years of my productive life at the
national accelerator outside of Batavia, IL as an inspector in the clean room doing
incoming inspection of parts for the accelerator. Most of my work was programing and
running CMM’s for inspection of parts that build a particle accelerator.
I done said all that just so you can feel confident that you’re not wasting your breath on
some guy in a suit and tie who spends his day in the office and got the bright idea he
was gonna pick up a hobby lathe off Crag’s list and become an overnight a machinist.
So…back to the subject. I’ve been on the net for a couple of months trying to find any
information on the way Logan intended for their Chucks to register. I’ve been reading on
several other forums, about the low end, threaded chuck attachments and since I’ve
removed the plate and reinstalled it several times and it seems to be repeating, I’m
going to go ahead and fit it up this morning.
But, I’m not 100% confident since this isn’t a backing plate from the manufacturer, who
by the way was still in business a few years back as Logan Actuator. I’m looking for that
definitive answer, which apparently doesn’t exist. But….that’s why I’m here and at a few
other forums asking for opinions, and believe me….there are a lot of them when you
talk chuck mounting.
These back plates I have are, as the catalog says, "Fully Machined Threaded Backing Plates",
which I take to mean, they have the thread tuned concentric with the OD’s and the chuck mounting holes
matched up to the intended chucks and that the faces are parallel to the thread axis.
The only thing that they should need is to match the step on the face to the back of the chuck. When I spin
the plate on it locks on very tightly which tells me that its in full contact with the nose of the spindle. When I
beck it off a few degrees there is about .006” to-.008”slop in the thread measured by the indicator.
One thing that concerns me is the face of the spindle has a step machined in it so that the back of the plate
only locates on this ¼” shoulder. This enlarged picture shows it quite clearly. The larger face on the spindle
is recessed slightly behind the cast bearing retainer. I have to check with the old chuck and see if
that is the plane of contact, If so, I may have to bore a shallow step to clear that shoulder.
Shars Chuck Backing Plate Runout photo - dennygraham photos at pbase.com
Din’t get much sleep last night because I really don’t feel confident in the way the new plate is going on.
Thanks for all the ideas.
Denny Graham
Sandwich, IL
 
.. still in business a few years back as Logan Actuator. I’m looking for that definitive answer, which apparently doesn’t exist.
No idea, personally, if he is still answering phone or emails, but Scott - at Logan Actuator - would be the first person I'd suggest contacting.

Logan Home Page

There may even be a factory-published single-page "how to" on fitup. If so, it will be every bit as valid today as it was fifty or more years ago.

"To soon, we assume.." that ALL Old Iron is 100% orphaned.

2CW
 
Ain’t that the truth. I’ve had a little old Wells horizontal band saw in the shop since the early 70’s
and one of the blade guides had been repaired by brazing many years ago before I got the machine.
Well, it snapped a couple of months back and I called Wells and low and behold, she was able to tell
me the year it was made back in the 40’s and they are still supplying OEM replacement castings for it.
Same thing with Scott at Logan. I ran up there a few years back and got a couple of new gears. I was
surprised that they still had some inventory for the lathes.
So…..my new Shars Chinese chuck. Mounted up the three jaw scroll chuck this morning and it runs out
about .0005” on a .75” dowel pin chucked up and the body indicates within .0006” to .0007”. Not bad for a
middle of the line engine lather that was made in 1946. And it repeats after uninstalling and reinstalling it
several times. Pretty happy with that since almost any chuck manufacturer will not guarantee a three jaw
scroll chuck to any better than .005”.
TIR .001 on chuck body photo - dennygraham photos at pbase.com
Come on John, my Large & Shapley isn’t that old……1916 not 1910. This is the one that a few years back
I was asking about on the L&S forum. It’s a 16” Selective Head but I’ve never seen another one with a head
stock exactly like this one and you said at the time that you never had either. The manuals that are available,
which are damn few show the Selective head lathes that are similar but not exactly like this one. And the
manual isn’t much more than a sales brochure for the lathes of that period. I still haven’t seen a clutch like the
one that is on this head either, which I would like to service but am leery about opening it up without a
manual or at least a picture of what’s inside for fear of damaging something.
Now…on to the 4-jaw mount up this afternoon.
tks once again guys.
dg
 
Don't quite understand the question?? There have been many times I've wanted to grip a large diameter item but had the jaws of my 6" chuck extended all the way. And at those times, the jaws were at their maximum extension. So, I was limited to how large of a diameter I could grip. Most everything I do now a days
is one of a kind for my self, so taking light slow cuts is the name of the game for any very large diameter
part. Time is not money anymore. At my age,it's not the time, nor the money, just simply the task at hand
and how well the result is.
dg
 








 
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