The Shop > CNC
Electricuting the lead screw
eskoilola:
--- Quote from: sparky961 on April 17, 2018, 10:19:52 PM ---If you're dreaming of rigid tapping in the future, a spindle encoder with a few thousand counts per revolution would be in order.
--- End quote ---
If the spindle is running at 1500 RPM there will be around 100.000 interrupts for the uC to be served each second. I know from experience that a PIC18F runniing at 64MhZ will be capable of serving around 30.000 intererupts per second if those interrupts are fast executing, simple things like advancing a counter. I know for sure that 100.000 is way too much.
awemawson:
If this lathe is to have an electrocuted lead screw, will you have to wear thick rubber gloves using it :lol:
https://en.wikipedia.org/wiki/Electrocution
(sorry I couldn't resist, your English is infinitely better than my Finnish )
AdeV:
You could maybe use a 2nd hand servomotor off a Bridgeport CNC mill, they pop up on eBay from time to time. I've no idea what the torque is, but you'd probably multiply it by running it via a drive belt anyway. And they have the encoder built in. You can avoid the need for a linear encoder on the saddle by using limit switches; at switch on, motor drives to one of the limit switches & that gives it a known physical position to start from. A decent industrial microswitch should have the repeatability you need. Re controllers - again, the Bridgeport controllers for those motors appear on eBay fairly frequently. I'm not sure what you'd need electrically & electronically to drive them though, I've not looked into it in great depth.
tom osselton:
--- Quote from: awemawson on April 18, 2018, 02:20:27 PM ---If this lathe is to have an electrocuted lead screw, will you have to wear thick rubber gloves using it :lol:
https://en.wikipedia.org/wiki/Electrocution
(sorry I couldn't resist, your English is infinitely better than my Finnish )
--- End quote ---
Igor throw the switch!!
PekkaNF:
Leadscrew electrocity :lol:
I have been reading some of the ELS projects and there are some. In principle it works like on any CNC lathe. Cascaded spindele servo and other servo for ballscrew. Enenough pulses per rev. and stiff servo loop = no problem.
Hobbyist tries to cope with rubberstring AC motor spindle drive, that will produce cyclic spindle speed that will slow down when punny threading tool hits the work.
And at the each start you must syncronize spindle and lead screw (ball screw) servo (stepper?) some distance from the start of threading. You need a lot of pulses and a controller when spindle speed will fluctuate during cutting.
Or much brute force the keep the system stiff.
I actually know one guy who bought servo drive for spindle and lead screw. This all is done in CNC controller and it seems to work well.
Pekka
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