Copying an eccentric bushing

I'm trying to repair a partly stripped spare headstock for a South Bend Heavy 10, as shown on page 2 of this:

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I haven't figured out how to make the back gear lever K+J, which moves the eccentrically-located quill shaft in or out of engagement with the spindle gears. My lathe is 30 years older than that manual and the spare probably older still, and they don't appear to have a separate bushing J, the lever and the eccentric bushing look like a single casting. The shaft is taper-pinned to the eccentric bushings at both ends so the shaft and bushings rotate together.

I got as far as drilling oversized round stock to fit on the shaft but now I don't see how to attach the blank for K to O to turn the outer bearing surface concentric and then move it to the far end of the shaft without losing rotational alignment. To complicate the problem the OD at J is 1.250" while O's is 1.625".

It would be easy if I cut key slots in the shaft, K and O, locking them together while turning J and preserving the angular alignment when I move K+J to the far end. Can you think of a method that uses the original hard-to-find SB shaft and part O without damaging them? jsw

Reply to
Jim Wilkins
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The exploded drawing seems to be showing only the right-hand end of the shaft is raised to disengage the small gear. The left-hand end is always engaged. And the lever and left-hand bushing are a single casting, as you wrote.

I wonder if someone else has repaired the machine and pinned an eccentric bushing at both ends, so both gears are disengaged?


Reply to
Paul Drahn

The drawing on page 2 doesn't show the shape of the parts accurately. Both end bushings are eccentrically bored to the same offset and pinned to the shaft with #2 taper pins, parts 91 and 102 on page 15, which shows the eccentricity more clearly. Shaft 94 is 0.748" diameter its full length except for grease grooves. The *** for 92 and 93 on page 16 indicates that the 10" model doesn't use them.

On my working lathe the backgear shaft remains parallel to the spindle as the lever K swings it in or out of engagement. I'd loan K+J from the good lathe to the spare as needed if the taper pin holes aligned, but they are shifted by almost the pin's diameter on the spare headstock.

I bought the spare headstock to make a large diameter wheel and pulley lathe, with the tool bit on an X-Y table that's manually aligned parallel to the faceplate so it won't require precision ways, just a rigid frame. It will definitely need working back gears.


Reply to
Jim Wilkins

Greetings Jim, If it was me I would first turn the O.D. of each eccentric. I would then drill an undersized hole at the taper pin location. I would then put a pin in this hole and use it to locate one axis of the eccentric hole. Then I would bore the eccentric holes. Finally I would ream the holes for the proper fit for the taper pin. I would the inspect the original shaft the bushings go on and make sure that both taper pins line up with each other and with the same axis as the eccentric. I would then correct any holes that were in the wrong place. In fact, the shaft should be done first so that you know on which axis of the eccentric bushings the pin should go. Also, do you have the proper taper pin reamer(s)? Eric

Reply to

I have larger and smaller taper pin reamers but not #2. There isn't much stress between the handle and shaft since its engaged and disengaged stops are in a slot cut into the handle's bearing surface and the friction shoe that keeps the gears engaged while cutting rides against the other bushing O. I was planning to clamp part K onto the shaft with a brass-tipped setscrew, possibly the handle itself, to avoid butchering an original SB part. People collect and restore these things.

Keeping both bushings on the same rotational axis both when turning part K while it's somehow clamped to O and then when attaching it to the end of the shaft is what I haven't figured out, but I got an idea using vee blocks and 3/16" shims while writing this. jsw

Reply to
Jim Wilkins

If you measure the distance "off center" for the eccentric, maybe you can machine the bushing in a 4 jaw chuck with the bushing fastened to a stub that is set with the same eccentricity. You could make two eccentric bushings with different diameters. Assuming that the pins in the shaft are in the same plane, the new eccentric bushings should be aligned too.

Reply to
Denis G.

Why not make it all as new parts instead of trying to work on the old ones?

Turn THREE eccentrics, then align drill/ream the pin holes. Now mill your slot in one of those. Remove the slotted bushing and stack it on a suitable section of shafting with the third eccentric and line them up. Make witness marks and pull them apart, now bore holes foe a pair of dowel pins on the adjoining faces. Turn a suitable handle and mill a flat on the outer bushing and weld the handle on. Drill and tap for a set screw to hold the piece to the shaft with the dowels fully seated.

Reply to
Steve W.

That is essentially my fallback position if I don't find a way to angularly align the new handle bushing on the existing shaft.

The small end of the #2 taper pin in "O" is 0.160" diameter so I can use a 1/8" or 5/32" roll pin to attach the new handle and maybe ream for a taper pin later.

I do have broaches to cut keyways to connect and align a new non-SB replacement shaft and bushings, and the eccentricity is low enough to drill offset center holes in the ends of the new shaft and turn it and the keyed-on bushings as a unit, like a built-up crankshaft. The main problem there is drilling both end's centers at the same angular position. jsw

Reply to
Jim Wilkins

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