adapting a tumble reverse from a 10k to a 9" south bend lathe

I saw a post on the practical machinist forum (this one) about switching out the 9" style tumble reverse for the more sophisticated version that was used on the 10k and much later 9" machines. Of course that meant I had to do it. After the usual ebay hunt I managed to find a reverse mechanism for less then a million dollars. Apparently I am not the only one who read that post.

The adapatation involves adding a steel plate that had drilled holes for the detent pin. This is NOT my drawing, but I am putting it here for thse who might find it useful.

I set about cleaning and putting in new oil felts.


The hardest part of reassembly was presing the "stud" gear back on.


Then it was time to make the adapter plate. I stared with a piece of cold rolled 1018 scrap I had around which had a few holes in it.

At first I thought I had gotten lucky and that it would work as found. However, after measuring it more carefully, it turned out to be too thick.  At the time I only had my little horizontal mill which did not really provide enough travel to do a good job. So into the 4-jaw it went for a facing to reduce the plate to an acceptable thickness.

Then I bored out the center hole for the tumble reverse, and put in a countersink for a bronze thrust washer. Total overkill, but I was excited to be making things!

Next I cut a groove in the tumble reverse shaft for a big circlip to retain it in the adapter plate (my one real modification to the original concept). You may well ask why I did it in reverse with that boring bar on the "wrong" side. I don't remember, but I assume it had something to do with clearing the spinning arm of death.


It fit! (never a forgone conclusion)

Here it is mounted up showing the washer and the shcs I had to cut down to clear the tumble mechanism.

At this point I had to locate and drill the holes to retain the detent pin. I followed a suggestion on the original Practical Machinist thread and made 2 brass drill bushings to fit in the handle.

Then I clamped the arm to the adapter plate and drilled the three holes in succession. No pictures of this part I am afraid. I got them close enough although there was some final hand fitting required to get the gears to mesh well in both top and bottom positions (center is neutral).

tumble reverse with pull knob from a 10k adapted to fit a 9" south bend model A lathe

It all turned out pretty well I think.