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Electronic Leadscrew for the New Lathe

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RussellT:
I made an electronic taper turning device which used a geartooth position sensor to detect the spindle speed and then stepped the top slide motor every x pulses for each tooth.  The software was very simple and runs on an old laptop but would easily fit on a Pic or similar.

The difficult bit in extending that idea is picking up the thread on subsequent cuts.  You could use a gear with a wide tooth to detect spindle position as used on some engines for crankshaft position sensing but the software would be more complicated.

My initial thought would be to use a stop to set a consistent start point and then start the cut on the wide tooth.

From a software point of view it would be easier to make it work with two sensors.

Russell

vtsteam:
Wow, I thought I'd wake up to maybe 2 replies.

Answers to various posts:

I don't mind a simple threading function. I don't plan to add an X stepper, and I don't lathe thread often.

A straightforward lathe (the one I'm building) with conventional acme screws. Anti-backlash nuts or spring or weight per ancient TurboCNC practice.

Reasonable practical thread accuracy for model engineering, not commercial/NASA/theoretical micron air bearing
ultimate spare no expense, etc. hooha.

Under $100 for a functional board so a 175 UK pound board, plus accessories doesn't fit spec.

I don't want to design and code something. I want to finish my lathe and build engines. Building the lathe is fun and rewarding, but it is in the way of building engines. I don't want now start also learning enough to design a circuit and program a microprocessor and have that get in the way of finishing the lathe so I can build engines. Hope that makes sense....

I don't mind soldering/populating a simple board kit if absolutely necessary, and if $100 or less. Or connecting up existing components (ie. an arduino, RPi, breakout board, stepper driver, steppers, power supply -- and I already have all of those components, or an encoder, which I don't have yet)

What I mean is the thread controller board -- whatever that is.

I have no prejudice against what is called a "Full CNC" solution vs an "Electronic Leadscrew" solution other than the size and comlpexity of an old honkin computer and monitor and cables all over the place in a tiny overcrowded shop on a small lathe. Actually, some of the electronic leadscrews actually look as big and messy as a full CNC rig so this may not even make sense.

The closest parallel to what I want is the ancient TurboCNC lathe at DAK, and if it worked well enough for reasonable threads and could run on a small Arduino sized board and interface with a couple line LCD would completely do it for me. I've used TurboCNC otherwise, and I speak DOS, so no problems at all and no prejudices about lack of bells and whistles.

John, I trust you know all of this, have been through it and probably do have a solution or the reasons to stop wishful thinking and get on with it.

Also, one more thing. I don't mind a mechanical rather than electronic leadscrew.

I just don't want to have to read a chart in tiny numbers in dim light on the left hand side of the lathe inside a cover with my head turned sideways, memorize those numbers on a particular line, find a wrench to fit gear retaining bolts, grab ahold of blackened oily gears remove them, loosen a greasy cast iron banjo and have it flop onto my thumb, put keyed spacers into the right hubs for doubled up gears, figure out which way they face -- behind or in front of each other, figure out which of three slots they go in, get that all wrong, remove the gears, wipe safety glasses with grease, apply to forhead, try gears again in a different slot, put a piece of paper in between gears to set correct spacing try to hold it in place while adjusting banjo, sliding gear in place, and holding a wrench to tighten simultaneously with only two hands, etc.

Then when finished threading, repeating the process to return to fine feed.

Is there an easier way -- and I don't want to make a conventional QC gearbox -- which project would seem to delay building the lathe to build engines even further.

Maybe something with timing belts to at least get rid of the grease?

Or what about a master thread deal, like Unimats had?

vtsteam:
Somebody needs to come out with a 5 volt single board computer the size of a credit card that runs DOS natively and has a CNC compatible parallel port and a B/W LCD display capability. Doesn't even have to be more than 100 Mhz  and look like a 486.

Or better yet, we need a DOS tablet, with a parallel port!  :lol:

John Rudd:
Rasberry pie......small board computer.....Doable?
I'd have thought so.... :zap:

vtsteam:
John, I've got one but the available CNC package, a GRBL interpreter which sends instructions to an Arduino board running GRBL itself, does not do threading.

The (or a) problem probably lies in the fact that communication is via USB, and so realtime monitoring and adjustment would be slower than some kind of parallel interface with lots of data in and out lines.

One other reason (said a GRBL developer) that threading is also a low priority, honest, I read this online, is because "lathes are more dangerous than milling machines," and the code would need to be more robust. These guys are 3D printer oriented.

Apparently this hasn't stopped other CNC programmers, and I'd hate to be locked inside the cabinet with a running Fanuc machining center.

Heading out now to cut some firewood wth the chainsaw......truly....


 

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