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Picking it up.

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DavidA:
With the (apparent) growing popularity of electronic lead screw drives I got around to wondering...

If for some reason you have to change the tool,  can you 'pick up' the thread in a similar manner to the way you can with a conventional leadscrew ?

Dave.

Note .. Edited to correct typo in heading.

vtsteam:
In my case I was planning on having a threading dial, and of course a half nut, since I see my particular lathe as a manual lathe, and the "electronic leadscrew" is actually only a replacement for the change gears. In fact, I'm not really comfortable with the term. To me an electronic leadscrew would basically be a single axis CNC lathe.

If you want to back up the threads, you could either switch off the encoder manually, or back it automatically by switching the direction input on the drive. That could be the same switch as reverse on the spindle drive. You'd have to make sure the spindle was completely stopped before switching direction electrically. But you should anyway.

You could also cut the thread manually with a handle on the spindle, because my particular design does not sample spindle rate, but spindle position, so is accurate at any speed, including big variations from hand cranking.

In fact I tested my new encoder without a motor drive against a stepper by twisting the encoder shaft. The stepper position and speed followed at whatever reduction rate was set.

If I set pitch to 1 it was just like a selsyn motor, mimicking the speed and position of the encoder shaft (other than direction). It was fun!

EDIT: well now I see it says "change the tool" re. picking up the thread. In that case, once you change the tool (and I assume you mean the position of the tip in the Z axis) you have to basically re-position the tip in the thread either manually (if you can rotate the leadscrew by hand -- and on my semi-manual lathe I will be able to) or by jogging only the leadscrew electronically. Spindle stationary. In either case you need to take up any backlash by making the move in the cutting direction.

This is the electronic geartrain equivalent of releasing the gears from the leadscrew, and positioning the cutting tip in the thread in a conventional change gear lathe.

awemawson:
Would you not be able to pick up the thread by manipulating the top slide? Let the electronics drive the tool half way (say) down the length of the thread, but displaced in X so not engaged, and then using an eyeglass adjust the said top slide so that the tool is in the correct Z position. (Top slide set parallel to Z axis) Obviously you have to do a few iterations advancing X as you get closer.

I cheat of course and use indexable inserts, so no resetting  :lol:

RussellT:
I wondered about having a stop to reset the tool to the start position,  setting the spindle to an index mark and then starting the lathe with the lead screw "engaged".

Russell

vtsteam:
I guess the answer to the original question is "yes" you can!

Hitting the inhibit signal (limit switch, emergency stop button, or a drive engage switch, etc. ) would be the simplest and fastest way of disconnecting the spindle and leadscrew and make for easiest repositioning by hand on my lathe, since it will have a leadscrew handle.

Also, the assumption of the question was how to handle a non-indexed tool replacement, out of position. The situation can arise with an indexable tool as well if you goof up and move the carriage disengaged, or the part needs to be moved, or moves, or for other dumb reasons yet to be mentioned!  :lol:  :lol:

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