OT kind of - Can you bypass a servo shift lathe mechanism?

Hello,
I've heard both good & bad about the LEblond servo shift, Cincinnati hydra-shift, etc. Is there a way to lock this set-up in a higher gear and use a VFD to get the rpm range you need? I have never been around one of these types of lathes. Are they really that tempermental? After searching on here, there were a lot of pros & cons , but no "Mcgyver" emergency fixes or conversions.
It seems that the machinery dealers, when they have 2 similar machines , the servo shift is is a little bit cheaper than the manual shift. Maybe it is due to other reasons not shown clearly in the pics.

Let me know the good, bad, and the ugly about the servo/hydro shift types. Also any quick fixes, adaptations, etc. that you have come up with.

Thanks,
JAckal

Just on general principles alone, the lathe has automated gear-shifting. A good analogy is a Monarch CK lathe where you have 4 gear shifter levers on the exterior of the headstock, and various combinations of the 4 levers at different positions give the discrete spindle speeds, except pulling those handles are automated.

It would have probably been simpler had they used independent directional "solenoid" valves attached to hydraulic cylinders internal to the headstock. A PLC would probably simplify things as well.

However, I believe it is built something like the controls of an automatic transmission* where the functions are integrated and some are mechanical fluid logic (ala air-logic).


* it does not "shift" like one however...instead there are likely dog-clutches which are completely independent and cannot be engaged simultaneously instead of friction clutches which have to be synchronized to "transfer load" as in an automotive automatic transmission

Having just completed a complete rebuild of a Cincinnati Hydra shift the answer to your question is:

"yes, the shifting forks could be fixed in one position"

But...... oh what joy to simply reach over and spin the dial

Very simple explanation of how it works is: the speed dial directs oil flow to the three shafts each which holds a shift fork. Depending on the gear selected the three shafts slide back-fwds to "select' the speed range.One, two or all three shafts may move at the same time depending on the gear selected.The shift forks slide gears into each other, hence the reason you must have a stopped spindle to shift.
A little oil pump in the headstock applies pressure to prevent shifting at the wrong time.

To me it's a very simple system.

To bypass you would need to make collars to fit over the exposed shift rods to prevent any movement.
Then disconnect the hyd feed line to the shifter block and probably disconnect the governor feed line also.

If there's a problem in the hydraulic part it's probably crud clogging the pump intake or an oil passage. Esp. as the gear oil in the headstock serves as the hydraulic oil. All the grit from gear wear goes through it...

The electrical side is more likely to fail but it's pretty simple. The zero-speed-detector that must trigger to enable shifting varies by generation, & may be flakey. The electric brake must function for shifting, and it can wear or the wiring can break where it flexes. The microswitches actuated by the fwd/neutral/brake/reverse selector can get out of adjustment.

If you were going to bypass the gear selection & VFD it, it'd be good to lock it in one of the belt-coupled speeds - I believe the upper 4 speeds are coupled to the spindle through the external timing belt for better surface finish. In the rest of the speeds, gears drives the spindle directly. The fork that switches between belt & "back gear" would be good to preserve as a manual range selector, since the VFD isn't going to cover the full useful range.

Bob

I have a 15 x 54 Cincy Hydrashift. If I wanted to convert it as you suggest. I would just shift it into highest gear and remove the shift dial from the front.
Mine would not shift properly when I got it and I removed the shift mechinism (kinda simple to do) and cleaned a lot of varnish off of the spools. And now it shifts perfectly. I had to ajust the clutch for proper detent too.
It is really nice to - shift speeds, take out of gear, brake the spindle to a stop. You hear a click-click and then you ease it back up to the new speed.

Thanks for the info , all.

So, they aren't that scary really. (If you try to understand them) & do a little bit of preventative maintenance.

That might make for me getting a better price if a dealer can't sell it because a few people are avoiding it like the plague.


Can you tell me what to look for and check ? Besides the obvious grinding & won't shift gears.

Are there some noises it should make? Can you tell me some of the common symptoms that are easy fixes/adjustments?


Thanks again to all,

JAckal