Gallery, Projects and General > Project Logs
Electronic Leadscrew for the New Lathe
vtsteam:
--- Quote from: awemawson on April 01, 2015, 12:38:27 PM ---
--- Quote from: vtsteam on April 01, 2015, 08:50:50 AM ---I was thinking about something like this:
http://www.ebay.com/itm/Encoder-600P-R-Incremental-Rotary-Encoder-AB-2-phase-6mm-Shaft-5V-24V-coupling-/321160456974
--- End quote ---
Amazing encoder that Steve, according to the description it has an 'output triode' - now valves, that's my vintage of electronics :lol:
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Andrew, which wire is the grid? :lol:
awemawson:
Joking apart - that is an amazing price for what looks to be a good encoder.
RussellT:
Hi Steve
I agree with your revised spreadsheet. The error isn't zero but the cumulative error is zero and the periodic errors are similar to the errors produced by the saw tooth profile of the stepper controlled cut.
My inclination would be to retain the 3:1 leadscrew gearing for smaller steps and more torque, and to increase the number of pulses, either with a different encoder or using the rising and falling edge method of frequency doubling as mentioned by Pekka and the ebay description you linked to.
I would do that because it would give more flexibility for cutting other threads - such as metric.
It would make the software more complicated, but if you built the hardware with more pulses then you could always upgrade the software and user interface when you needed an odd thread.
Russell
vtsteam:
--- Quote from: RussellT on April 01, 2015, 03:48:53 PM ---Hi Steve
I agree with your revised spreadsheet. The error isn't zero but the cumulative error is zero and the periodic errors are similar to the errors produced by the saw tooth profile of the stepper controlled cut.
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For Integer inch pitch threads, there is no error in the ability to send steps on time in relation to the spindle position. which is what counts as far as the thread is concerned. There is no periodic error in those threads.
It has nothing to do with the stepper's steps per inch. Only the spindle and step timing matters.
re. increasing encoder fineness -- I don't want to do rising and falling edges for the reason Pekka mentioned, and for practical purposes a 1.5 to 1 reduction to the leadscrew will fit the lathe better. This is a small lathe, and I think a 400 oz.In stepper will handle it.
If for any reason that doesn't work well, it would be easy to change, so I think that's the way I'll go.
vtsteam:
--- Quote from: awemawson on April 01, 2015, 02:55:40 PM ---Joking apart - that is an amazing price for what looks to be a good encoder.
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Sent for one. :beer:
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