Hi All,
The cross slide on my 9 inch south bend advances .002" per mark and I would
like to have it so that it advances .001" per mark. Anyone have one like that
that wants to trade screw, nut, and collar?!
Rick
Are you getting this from measuring the cross-slide travel
directly, or from measuring the change in diameter of the workpiece?
If the cross-slide moves 0.001", the diameter should change
0.002", because that amount of metal is taken from both sides of the
workpiece.
You can get collars (for some lathes) which read out directly in
diameter change, instead of radius change -- in which case for 0.001" on
the dial, you would actually *move* 0.0005", not 0.002".
I suspect that all you need to do is to get a replacement
*collar* (or to *make* one). I don't know whether South Bend ever made
direct diameter reading collars. I'm quite sure that the leadscrew and
nut are no different on the machines so fitted.
But the easiest way to do this is to get a DRO for the lathe,
Shooting Star is one of many, and fairly inexpensive as they go. Most
have a button which will change the Y-axis readout to give either
radius or diameter readings, depending on what you need.
Or -- do what I do, and keep a calculator near the lathe, in a
ziploc baggie, with the buttons and readout facing the clear side, so
you can use it without oil, cutting fluids, and swarf getting into the
calculator or jamming the buttons.
Good Luck,
DoN.
P.S. You'll even find some compounds set up for direct diameter
reading -- which really does not make any sense, given that for
normal threading the compound is *not* parallel to the
cross-slide, but at an angle -- usually around 29.5 degrees, and
when you turn the compound parallel to the ways to crank off
known step lengths, you will want it direct reading or you will
have to keep a calculator handy.
Quite right, the leadscrews are idenetical.
The "direct read" (0.0005 slide movement per division) dials
from southbend are simply larger diameter than the ones that
give 0.002 stock reduction per division.
At one time SB only sold the new, larger dials as an
entire replacement unit with nut and leadscrew attached.
Big money.
However the larger dials and the larger "bushing" (here
bushing is the part of the dial that threads into the
carriage casting, and upon which the dial itself rides
on) can be retrofitted to a good-condition lead screw
by doing a bit of fiddling.
'
Basically the SB system has a round collar that the dial
rides on. The dial is locked to the collar under normal
operation via a setscrew and small brass pusher pin.
The collar itself is locked to the leadscrew with a sort
of dutchman pin - a small, soft steel, cylindrical pin
that is inserted into a hole that is half in the leadscrew,
and half in the collar. Said hole is drilled in final
assembly and will *not* be right if the collar is changed
out with a new dial setup. But there is plenty of room
on the other side to drill another hole and put a new
dutchman in there.
When this retrofit is done it is important to get the
axial clearance in the stack to be correct. The leadscrew
has a shoulder on the inboard end, which constrains one
end of the stack. The small strange slotted nut bottoms
on the outboard shoulder end of the leadscrew and defines
the total available clearance for parts that are spinning
on the screw. This includes the bushing, the collar, the
dial (collar and dial are typically nested so they both
have to be considered). The collar has to be taller than
the dial so that the dial can spin freely when the setscrew
is loose.
As an aside, if the dial clearance is too small, the dial
will tend to creep on the screw even if the setscrew is
tight.
Basically the entire stack wants to see a thou or so of
clearance to allow it to spin freely. Too much will
cause needless backlash in the crossfeed.
The clearance is adjusted by either shortening the bushing
or facing the innermost leadscrew step deeper (increases
clearance) or by cutting the outermost step on the
leadscrew - the step that the nut bottoms against - deeper.
This decreases the clearance in the stack.
Jim
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please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
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They did make them. Not quite so simple, the bushing that the screw
goes into in the carriage will have to be remade, larger, of course.
This carries the index mark. Threads in, 3/4"-16 on my model A. What
I don't know is if it was ever made to fit the Model A, as the lathe
was made for for a home shop type environment. I have a complete
setup here, cross slide only, from a larger, (I think) machine,
exactly nothing is compatible from that one to the A. The only
similarity is the 10 TPI.
The absolutely did make them for the nine inch machines.
When I had my 9" model A, that was one thing I did, I
purchased a new replacement crossfeed screw assembly
from them with the large dials. I left the compound
alone though, with the smaller dial.
That was actually some of the best money I spend on that
machine, as far as upgrades go. The older leadscrew
looked like it was sharp-V threads, it was so badly
worn.
Jim
==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================
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