South Bend Cross Slide

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.

My SB 14 1/2 X 72, mfg. 11-24-48, has direct read collars. They appear to be the originals. Was it an option perhaps?

Bill

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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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

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Thanks everyone for your suggestions. I am going to see if I can buy a collar and if not I'll make one. Thanks again, Rick