eccentric turning

Thanks Andy, I still have the 2 axis config backup . I'll redo it tomorrow morning and let you know how it works out.

I have something working, I cleaned up the HAL file and changed the line to link the encoder position to the offset angle but it seems I need to scale the encoder position to degrees. I find that the raw position is giving x axis motion that is too slow to produce the desired
pattern.

My encoder is a 4000 count device (1000LPR) so the encoder scale is set to this value. The position value is derived from encoder counts divided by scale so this is proportional to angular position . How do I create a signal in HAL to scale the position x 360 (degrees) and limit it in the range of 0 to 360?

I'm wondering if the eoffset-per-angle component does a modulo 360 internally . I think it might and that would solve one problem.

As an experiment I changed the encoder scale to 11.111 which (4000/360) which suggests the correct amount of movement per rev of the spindle but I'm no expert at HAL. I need to preserve the encoder scale at 4000 to ensure my spindle sync moves work.

I realize spindle needs to turn slowly <100 rpm for this to work, back gear would be nice.

Yes, the eoffset_per_ angle wants to work in degrees:
github.com/LinuxCNC/linuxcnc/blob/master..._per_angle.comp#L313

Easy thing to try, ask for a 360 * N polygon, it might work.

Alternatively, pass the angle through a scale comp

Peter_Cassar wrote: I realize spindle needs to turn slowly <100 rpm for this to work, back gear would be nice.

I have been considering a sub-spindle:

second-from bottom 2 pictures here: www.lathes.co.uk/holbrook/page4.html
And a home-made one: www.practicalmachinist.com/vb/bridgeport...experimental-207139/

An important point from that second link is that you don't need a set of spindle bearings, you can use a live-centre in the driven spindle, and arrange for a drive-dog plate to simply rotate relatively slowly around it while the live-centre body spins at full spindle speed.

Andy, That's done the trick. Just for reference below is what I added to my main hal. The signal spindle-degs is referenced in oap.hal because for some reason the system couldn't find xo from the main hal. The motion appears correct now that the encoder position is scaled to degrees. Thanks for your help and I'll try turning a hex nut today.

<--hm2_stepper.hal-->
loadrt scale
addf scale.0 servo-thread
net spindle-revs scale.0.in
net spindle-degs=> scale.0.out
setp scale.0.gain 360

<--opa.hal-->
net spindle-degs => xo.angle


About the slow spindles. I was thinking of an auxiliary worm drive off the rear of the headstock spindle that I could engage/disengage and driven by an ac motor or even a servo would provide plenty of torque . The current spindle arrangement on the lathe has not much torque below 100rpm.

I have a 16inch lathe like the one you linked to in your last message. It's got a reduction gearbox before the spindle drive and the lowest backgear speed is 15RPM . The planetary drive is a great idea although I would have to add an encoder to the output shaft which wouldn't be too much of a challenge.

Peter_Cassar wrote: I have a 16inch lathe like the one you linked to in your last message. It's got a reduction gearbox before the spindle drive and the lowest backgear speed is 15RPM .

That might be slow enough.

The planetary drive is a great idea although I would have to add an encoder to the output shaft which wouldn't be too much of a challenge.

If it is geared then the ratio is exact, and just scaling the normal spindle encoder differently will do the trick.