Another daft idea, electronic lead screw.

Gallery, Projects and General > How do I??

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BaronJ:

--- Quote from: John Hill on March 15, 2014, 08:26:30 PM ---First off, I know a lot of people have done this and I know there is much debate as to it being a worthwhile project but I would like to at least dip my toe in the water with regard to the subject of CNC.

I have a nice stepper which might be big enough for the job and I have been looking under the cover of my generic Chinese 12x36 lathe.

The idea is to mount a stepper with a pinion to engage with the 120/127 compound gear when the banjo is swung away from the spindle pinion (no issues then of having electronic and mechanical drive engaged at the same time!). That bit looks simple enough.

Then I need a spindle encoder but fixing anything to the spindle might be a challenge due to the big hole that has to be kept clear right through the middle! There is the pinion that turns at spindle speed and normally engages the 120/127 compound gear but fixing anything to that would be a nuisance when using the normal mechanical drive scheme.

There is another option and that is to attach an encoder to the drive pulley which is geared to the spindle. It turns at a more or less constant speed of about 700rpm. If I used that to mount my encoder the encoder would be turning faster for most (all?) threading operation and slower than spindle speed when high speeds are selected. Obviously my software would have to be told what drive gear was engaged.

There is so much to think about! : :scratch:

--- End quote ---

Hi John,
Grab your self an old computer mouse, the type that has a ball in it. Inside are two slotted wheels and the optics that sense them. There is also the circuitry to detect rotation and feed out the signal. They require a 5 volt supply and output a 3.5 volt square wave.

tom osselton:
Nevermind just a brainfart!

JohnHaine:
Stick a one pulse per rev encoder on the spindle, drive the leadscrew through a 2:1 toothed belt from your stepper, control it with mach3. You'll never look back...

JohnHaine:
By the way the simplest way to make the encoder is to stick a small rare earth magnet on the spindle and use a Hall effect sensor. See Tony Jeffree's website for details.

velocette:
Hi
Not a "Daft Idea" at all. But unfortunately it's been done before. Click on the link it may help

http://www.homemetalshopclub.org/projects/electronic_lead_screw/els.html

Bit over my head I'm afraid

Eric

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