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Electronic Leadscrew for the New Lathe

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Arbalist:
When you think about it, it's surprising someone hasn't come up with some kind of swappable lead screw system. Not as elegant as change wheels but could be much quicker to set up?

sparky961:

--- Quote from: vtsteam on March 28, 2015, 01:19:49 PM ---... I do have an old Win95 NEC 486 DX66 laptop, that will run DOS on startup, actually in quite good condition stuffed away somewhere "in case I ever found a use for it"...

--- End quote ---

Old laptops that are too slow to use modern software find a perfect place in hobby CNC if you use old software or something of your own creation.  They are compact and more powerful than most people give them credit for.

The only issue I've come across in my own experience is that the processor speed can limit your maximum stepping rate.  There may be a way to get around this, but just another factor to keep in mind while you're exploring options.  It was definitely better when using "good old" DOS and TurboCNC rather than Mach3 and Windows 98.  The multitasking (task switching) nature of Windoze is the core of the problem when you're trying to do something that requires real time operation.

I never had much luck getting EMC running well on any computer.  Unfortunately my experience with other open source linux-based software seems to follow the same pattern.

vtsteam:
Arbalist, I was thinking similar to those lines, but  a normal leadscrew with half-nut and a second parallel pushrod to the apron -- attached there with a clamping block.

Pushrod goes back through the lower front headstock area (similar to the leadscrew) to the thread pickup arm, which rides on the spindle master screw -- similar to above pics. All the connections on the pushrod are adjustable, also similar to pic above.

You can still use the conventional leadscrew, but for threading you open the half nut and clamp the pushrod to the apron. It then controls the carriage.

In other news:

The NEC lappy is a Pent 1 it turns out, but the HD seems to be missing (did I do that?) It boots to BIOS, but the floppy drive is defunct. The HD socket connector seems to be proprietary, so I can't just drop in one of my old lappy HDs. Probably a lost cause. Too bad.

Mechanical solution is looking kinda attractive at this point unless someone comes up with a cheap simple electronic leadscrew controller board. Still open to ideas there.....

PekkaNF:
I was about to play with velocity-tracking AC-inverter, but lost momenum...I have few 100/200W and 400W AC drives that do all sort of tricks and I think I guestimated that chucking even unmached pair of AC motors and invertters together would produce me near perfect feeds.

But there is a guy 20km away that could not stop there but used servocontroller to drive lead screw in velovity mode. If I remmber correctly he had to use eventtualy some sort of panel for user controller, but no PC, no progam licences, no mouse, no keyboard......all the smarts were on servo drive. This might or might not fit to your budget.

I like that tread follower idea too, it's all mechanical, simple, easy to understand and there will be no cheap caps to blow up their tops. I would design it at the back of the machine and normally the threads would be made away from the spindle....at great speed.

This should give you a push:
http://www.lathes.co.uk/carstens/
http://www.lathes.co.uk/stedall/
http://www.lathes.co.uk/accuratool/

just look her curves:
http://www.lathes.co.uk/accuratool/img2.jpg
That is one interesting design, but it has the horrors. But it brings your arm out of harms way.

Pekka

Fergus OMore:
Not wishing to wander too far off but others have mentioned simplified screwcutting gear boxes.  I had one!
I made it up to the design of Martin Cleeve which appeared in ME in the 1950's

Somewhere are the drawings but it is shown in his Screwcutting in the Lathe book. It covered what he needed to cut Imperial threads and whilst I have a full Myford box and a metric conversion, I recall his comments about 'tieing up' gears. I recall him saying that Prof Chaddock had calculated that 20 change gears could be arranged to cut 750 thousand pitches- if they were not locked in a box.

Not for me to try- counting the odd sheep is enough for me.

Good night

Norman

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