Considering a Full Rewire on a Working Schaublin 125 CNC

The trick to freeze the VFD PID when not on the limits might be to set maxerror to a very small number (actually = 0 means "no limit") using a mux component.

I think I don’t fully understand how that would work. The variator is controlled by two contactors. The shortest time that has to be on to actually change the variator state is relatively long. And how would you turn the float from a PID into the contactor signals?

Did I understand you wrong?

Today I tried threading with G76. It did not go very well (see picture). It looks more like a very rough turning pass. I am not sure if I understand the parameters of the cycle. It is supposed to be M32x1.5.

The code I ran was:
With this, the material was not touched at all, so I started at X32.5 instead of X34 (that is where the picture comes from).

Are the parameters I and K relative (and in radius)? I thought starting at X34 is, in radius, 1 mm away from the nominal 32 mm I want, so I = 1, and the pitch is 1.5, so the final depth should be 0.75 mm lower.

The lines in the GUI looked just like “Figure 4. G76 Example” from:
linuxcnc.org/docs/html/gcode/g-code.html#gcode:g76

Can anyone give me the G76 line for an M32x1.5?

1) To operate the contactors from a PID you could use a WCOMP HAL component. Use the "over" and "under" pins to drive the contactors and set up the max and min some small distance above and below zero to prevent hunting.
linuxcnc.org/docs/stable/html/man/man9/wcomp.9.html

2) Before looking at the G76 G-code, make sure that spindle.0.revs increases by exactly 1.0 for every rotation of the spindle.

The main errors:
K0.75 is radius mode while in diameter mode.
I1 is radius mode (X34-X32) while in diameter mode
G96 D2500 ? 2500 m/min surface speed? Cutting steel with carbide  is typically only 1/10 that or less.
Maybe consider G97 S500 just to remove a variable while you are getting used it it?

Assuming a thread major diameter (stock OD) of 32, with you drive line at  X34, I-2. In practice, the major diameter is probably more like P/8 smaller. Somewhere around 31.8mm. Andy has programmed all that into his lathe macros, so you just give it major diameter (32mm) and it takes a first turning path at P/8 smaller before starting threading.
Since this is G7 diameter mode, the final depth K is also in diameter, so that will be 32-30.5 K1.5. Actually it is more likely to be about 30.38, so you will tweak this number to get your thread to fit, if you don't have perfect full profile inserts. Dont be surprised that you need around K1.62 to get the nut to fit.
J0.3 is reasonable. You will need lots of passes. See if you can get the insert to survive at J0.5
The R 1.6 means your cut will get heavier at each pass. I tend to set that at R2 for constant area, of course leading o increased number of passes.
The rest looks good.

G7 G18 G21 G90 G94
G0 X34 Z10
G97 S500 M3 M8
G76 Z-15 P1.5 I-2 K1.5 J0.5 Q29 H2 E0.75 L2

RotarySMP wrote:

G96 D2500 ? 2500 m/min surface speed? Cutting steel with carbide  is typically only 1/10 that or less.
Maybe consider G97 S500 just to remove a variable while you are getting used it it?


 

"D" is max spindle speed, not desired surface speed.

Thanks for the replies. The spindle.0.revs seems to be right when turning by hand, and when driving with the VFD active it is hard to tell exactly, but it seems to be correct as well.

Trying in constant speed instead of surface speed is a good idea, I will try that next.

And regarding diameter and radius, the man page I even linked says:

Note: When G7 Lathe Diameter Mode is in force, the values for I, J, and K are diameter measurements. When G8 Lathe Radius Mode is in force, the values for I, J, and K are radius measurements.

I don’t know how I overlooked that, it is really obvious now.