Crossfeed backlash question, SB 9A

Hi All,

I'm in the process of cleaning up my "new" 1950 model 9A. Pulled the crossfeed screw and after cleaning and re-insertion, I notice that there's some axial play between the screw and the saddle. The collar that threads into the saddle casting is all the way in.

Is there an adjustment hiding here somewhere? I didn't remove the crank from the end of the screw - appears to be a drive fit with axial pin to prevent rotation. Do I just need to drive the crank a bit farther onto the screw?

Thanks for you help,
Jeff Greenblatt

Hi Jeff,

When you say axial play, I take it you mean in-and-out play of the screw shaft in the collar?

Working of this assumption, the ball crank handle butts a shoulder on the screw shaft. So, it will only tighten up to a certain point. Generally what happens is the thrust surfaces on the screw and/or the collar and dial wear and the "play" develops. Some people shim under the graduated dial to minimize this but the proper way to repair this is to re-fit the shaft to the collar. This entails removing the cross feed screw assembly and disassembling it. Measure the in-and-out movement of the assembly first. Then chuck the screw up in the lathe and machine off the same amount (leaving .001" for free working clearance) from the shoulder the ball crank butts. This is the procedure used when screws were first fitted to the lathe.

I think I remember that you have (had) an Atlas lathe. You can use that for making repairs. You can also use the South Bend Lathe by locking the cross slide (by tightening the gib screws up) on its slide ways and positioning the compound at zero degrees. This way, you can use the compound screw as the cross feed. Unfortunately, you won't have a power feed but the shoulder is very narrow and doesn't really present a problem.

Sometime I should stop by an see your setup. I travel frequently over the Wm. Preston Lane Memorial Bridge (The Bay Bridge) and have in-laws in Annapolis.

I hope this helps. Good Luck!
-Blue Chips-
Webb

What Webb said.

Over time one will see a gap develop between
the graduated dial and the 'bushing' that threads
into the front of the carriage.

South bend calls this a 'bushing' but it is
nothing more than the front part of the mount
for the crossfeed screw.

Most times the wear leaves circular grooves
on the outer face of the bushing, and the inner
face of the graduated dial.

Also there is comparable wear on the *other*
end of the system, which is between the flange
on the inside of the crossfeed screw, and the
underside of the bushing.

I like to remove the entire setup by unthreading
it from the carriage, and dismantle it so that
I can inspect all the wear surfaces.

There is only one way to tighten this system
back up again, and that is to reduce the
length of the shaft that the handle butts up
against. Basically the clearance is set by
the lengths of the bushing and graduated dial,
compared against the distance between the
inside of the lowermost flange surface measured
up to the underside of the knob.

One thou or so is a nice number. The graduated
dial 'floats' on the shaft under the handle
so it needs some axial room.

The trouble happens if there has been a great
deal of wear, and one wants to take a skim
cut off of:

The top and bottom of the bushing,
The underside of the graduated dial,
The inside of the screw flange.

All this adds up after a while and then
when one goes and faces off the top of the
screw so the knob goes on farther, one runs
out of thread to attach the handle to the
shaft. The threaded portion is quite short,
only one or two threads. Because SB undercuts
the end of the thread into a groove, one
can wind up without enough meat to put the
funny slotted nut on.

So inspect what you have carefully and if
you are going to clean anything up (aside
from just adjusting the clearance) then go
real easy.

If you reduce the clearances *too* much
you will find that the graduated dial wants
to 'stick' to the bushing when you are turning
the handle clockwise.

Also be sure that the brass shoe is under the
clamp screw for the dial.

Jim