Funny;
My lathe never had a back gear shifter. Gone. I blew this thing down nearly a year ago now. I'm putting everything together now, and it takes a lot of jiggering and fiddling to get all the spacings correct. Set and reset the gears and such to get it all clearanced. I've been fiddling with the back gear shifter for a while, on and off, but not really intending to lock it down just yet. That's more toward the end. Something about it didn't quite figure, but I wasn't sweating it.
Painted the bed last night, and the headstock cover tonight. I was fiddling with that shifter again tonight, and it still was not making sense to me. I note the locking tab would slip into the case. Hmmm... The end is rounded off. Won't catch. No problem. Pushed the pin out, ground the end of the tab flat, and slid it back together. Still slipped through. OK... tab doesn't stick out far enough. Simple. Slid the tab back out and ground the other end where it bottomed in the slot at rest. Perfect. Sticks out and locks solid. Still this thing doesn't make sense.
I slip the shifter in and engage the back gears. Works. Slide it out to disengage the back gears. OK. Wait... this doesn't make sense. The tab locks it out of back gears? It sticks that far out most of the time? The shifter slides out so far that the back tip of the shaft doesn't stick out far enough to put the locking collar on the end?
Good fortune came in the form of the complete spare headstock I bought for parts sitting there on the bench. Shifter and back gear shaft still in place. No locking tab on this one, but shifting it back and forth, smooth as silk. Wait... isn't this working opposite? Push it in to disengage, pull it out to engage. YES! Now the lock tab makes sense. It locks the shifter OUT to hold back gears IN. I've got the rebuilt one backwards! Who knew? You've got to hold the eccentric back gear shaft up with gears engaged before you slip the shifter in. Works like a charm.
Hey.... I got this!