Member postings for sam sokolik

Constant surface speed and feed per rev example with linuxcnc.. (about half way through the video - I ramble)

I enjoyed this one.. (but he is using linuxcnc..) He is up to 25 episodes

I guess I don't know how it is pronounced... Hard of soft G? Because of the e - it should be soft... But no clue.

Edited By sam sokolik on 08/10/2020 19:55:24

The down feed wasn't working and finally dug into it. The pawl was sticking and the key was missing from the downfeed lead screw/drive gear. Back in business!

Edited By sam sokolik on 08/10/2020 14:40:58

I have been thinking about a few ways to send the component a shape to cut. certainly possible. Time - where is all my time!?

This is actually how linuxcnc works with external interface hardware. (not a motion controller as the motion controller is in software - linuxcnc) The external hardware just does the stuff computers don't do well (fast encoder counting, High speed step generation, Pwm generation and such) Linuxcnc is running a realtime thread that polls the external hardware every 1ms (or 500us or whatever the system can handle) It gets the encoder counts, sets pwm levels, sets step rate and so on. This works very well. (as a cnc controller and hobber as others have shown)

The other thing you get with with a computer running linuxcnc - floating point calculations. (this is the stuff the computer does well)

sam

I have been playing with linuxcnc on the RPI 4. Linuxcnc requires a realtime kernel. (in this situation - rt_preempt)

The thing with linuxcnc is you get a whole bunch of realtime building blocks. Like step generators with vel and acc limits, pwm generators, logic and tons of other pre-built realtime components. (plus you can make your own)

All of these components have been tested and are done

This was done on a RPI 4 With a custom realtime component - slaving the axis to spindle rotation. (well - most all the latest videos about the green machine are done with the rpi)

Just a thought. Sir John did a bit of work on gear hobbing and ended up using Linuxcnc... You could even start with the printer port... It is a cool platform/framework that allows for a ton of easy development.

That was all by hand gcode. The actual polygon turning is currently done by sending info to hal layer from gcode.. I hope to do a remap but I am not there yet. So something like (this is on the mill - polygon boring)

(polygon radius)
m68e0q.30625
(number of sides)
m68e1q6
(Cutter diameter - probably get from the tool table in the future)
m68e2q.375
(rotate poly 0deg)
m68e3q0

(enable polygon component)
m64p0

(disable polygon component)

m65p0

more close up action...

Agreed - I was unprepared for the first run of the program.

Getting there

some machining required...

A bit of an update

Yes - some Pitmann servos that came with 500 line encoders. I am using Mesa interface hardware that does the high speed pwm and encoder counting. (5i25) which acts like 2 super high speed printer ports. (expandable - you can get daughter boards that do all kinds of cool stuff - analog servos, steppers and such)

I am using it in kinda unconventional way (think cheap a$$) (mesa + cheap bob)

addendum... There was a setting in the ini file that was capping the acceleration at 6in/sec^2.. No wonder why it looked so good. So - upping the acceleration to 50in/s^2 I get a peak following error of .0002" (10 encoder counts - which is exactly what I would expect) Now it feels as expected - accelerating to 150ipm is pretty instant.

sam

I finally got back to the Emco project after a few years. Squirrel! I had thrown it together trying out some pwm drives I had - which seem to work great. When I started pllaying with the spindle I started getting noise. (sporadic estop pulses). (mainly because in my excitement of the servos working well - I didn't pay much attention to grounds..)

So - Taking the time to do it right.. (I want a little lathe to test the polygon turning..)

Currently the servos are tuned with a max following error of .00007", acceleration of 40in/sec^2 and top speed of 150ipm. Very happy with this - and it looks like I could up the acceleration.