Screwcutting

That is a lot different than my scope trace. Yours seems to be random bumps where mine is real steady. You might have some electrical noise on your encoder lines. Do you have the shield grounded on one end only?

John

welderfabrod wrote:

Also I'm still getting what I feel is the odd motion of the rapids outside the drive line. Now the point is, is this how the G76 in EMC2 has been implemented or is it just me having this problem.

I don't know if you are still watching this thread, but it is not just you. I have exactly the same issues and have been wrestling with them for some days now.

1) The spurious +X jump disappears with an M1 optional pause before the G76. Perhaps a G4 pause would also do away with it?

2) Jerkiness. This looks like a badly tuned controller in the internal conrol loop in spindle coordinated motion. The job of G33 and G76 is to look at the encoder position and to make sure that the axis is in the right place. This requires a controller, possibly a full PID one, inside the software. This looks to be badly tuned (or to be well tuned for a different machine, as it seems to work for others) .
It seems that the axis is overshooting, pausing to let the spindle catch up, overshooting again. You can elimibate this by cranking the spindle speed up so far that overshoot is impossible, but then you get an arbitrary and wrong thread pitch, so it isn't any help.
Firstly, you can feed this controller with a much smoother encoder signal by making the following change to your HAL file:

setp encoder.0.position-scale 100
setp encoder.0.counter-mode 1
net spindle-position encoder.0.position-interpolated => motion.spindle-revs
net spindle-velocity encoder.0.velocity => motion.spindle-speed-in
net spindle-index-enable encoder.0.index-enable <=> motion.spindle-index-enable
net spindle-phase-a encoder.0.phase-A
net spindle-phase-b encoder.0.phase-B
net spindle-phase-index encoder.0.phase-Z

This didn't actually work for me, so I am going to try some more experiments.

1) Try different control modes, (G61, G61.1, G64) perhaps the version with a programmable error is better, or maybe exact stop mode even.
2) Try working in imperial. I have noticed that the only people complaining (Me, yourself and Archivist on IRC) are using metric. Perhaps the controller is tuned for much smaller numbers?

G61.1 Does help, but not enough in my case.
G61 is also an inprovement.
G64 P (silly big number) is definitely worse.
I created an imperial config for the same lathe, and it seemed fractionally better, but that could have been luck. Having an imperial lathe might be useful anyway at some point.

There has been an awful lot of debate on this on the mailing list and the IRC channel.
One thing that is clear is that there is more that one way that screwcutting can go wrong.
There is a suggestion that my problem (regular osciallations of the carriage)m starts with a bad initial velocity estimate, and never recovers. There is a software patch being evaluated that should improve things if that is the case.
However, somebody else has demonstrated a problem with noisy encoder signals, and that causes a similar but different problem. If halscope shows a similar problem for you then the quick-and-dirty solution is debouncing in the HAL file.

Add lines like these (with the correct pins referenced, and a B-channel added if you have one) to your custom.hal (or in the main machine .hal file if you want, then you can ignore the unlinkp statements.


loadrt debounce cfg="2"
addf debounce.0 base-thread
setp debounce.0.delay 2

unlinkp encoder.0.phase-A
unlinkp encoder.0.phase-Z
unlinkp parport.0.pin-13-in
unlinkp parport.0.pin-15-in

net indexunfilt <= parport.0.pin-13-in
net indexunfilt => debounce.0.0.in
net indexfilt <= debounce.0.0.out
net indexfilt => encoder.0.phase-Z

net spindleunfilt <= parport.0.pin-15-in
net spindleunfilt => debounce.0.1.in
net spindlefilt <= debounce.0.1.out
net spindleunfilt => encoder.0.phase-A

It sounds like it is unlinking the pins, but not relinking correctly.
Did you just paste in my HAL instructions, or edit them to suit your setup?

Which pins are your encoder wired to, and how many channels does your encoder have?

You should be able to get back to where you were by just deleting the new stuff.