MACH4 makes an arc in a corner

[dune1982]

Hello Forum,
i guess there must be an on/off switch for this in MACH4 but I don't know where.

This code should generate a rectangle:
(60.3, 65.3)
G90
G91.1
G00 X37.5 Y42.2
M3
G01 X37.5 Y44.7 F1500
G03 X35.0 Y47.2 I-2.5 J0.0
G01 X22.8 Y47.2
G01 X22.8 Y22.8
G01 X47.2 Y22.8
G01 X47.2 Y47.2
G01 X35.0 Y47.2
G03 X32.5 Y44.7 I0.0 J-2.5
M5
G00 X32.5 Y65.3
M3
G01 X32.5 Y62.8
G03 X35.0 Y60.3 I2.5 J0.0
G01 X60.3 Y60.3
G01 X60.3 Y9.7
G01 X9.7 Y9.7
G01 X9.7 Y60.3
G01 X35.0 Y60.3
G03 X37.5 Y62.8 I0.0 J2.5
M5
M30

MACH4 shows the correct preview, but when i start the programm in every one of the four corners the laser travels on an arc that is not in the NC-Code.

So I have a rectangle with rounded corners.

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[Formantjim]

Just tried your code in UCCNC and it works perfectly must be some setting in Mach 4 that is either not set or corrupted.

[Jim Dawson]

It would seem that the arcs are in your G code, with a 2.5 radius.


.....
M3
G01 X37.5 Y44.7 F1500
G03 X35.0 Y47.2 I-2.5 J0.0
G01 X22.8 Y47.2
G01 X22.8 Y22.8
G01 X47.2 Y22.8
G01 X47.2 Y47.2
G01 X35.0 Y47.2
G03 X32.5 Y44.7 I0.0 J-2.5
M5
.....

[dune1982]

those 2.5 radius arcs are lead in and lead outs.
This is how the NC-Code looks in the preview:


And while machining MACH4 adds these arcs (in Blue):

[dazp1976]

Looks like it's doing something to do with "smoothing around corners".
Could be something selected/checked in cam/post script that doesn't show up in simulation.

[dune1982]

There must be a setting in MACH4 or an M / G code that I do not know, that will activade/deactivade this behaviour.

[Shadyoak]

It is most likely Your constant velocity setting, Mach creates round corners to keep speed constant. You can turn off in control and check Exact Stop but your machine my run slow or make a lot of jerking motions.

[joeavaerage]

Hi,
Try using Exact Stop mode to see if the behaviour changes, in the Mach/Control/Defaults plugin.

If Exact Stop improves the corner rounding then you must either continue using Exact Stop OR improve your Constant Velocity settings.

The most overlooked problem is that you have a machine acceleration which is too low. Most people have the max velocity wound up as high as they can without
losing steps but then have to limit the machine acceleration....mistake. High acceleration = best toolpath following, and incidentally often the best overall machine
speed and minimum cycle time.

Try halving the machine velocity but increase the acceleration until you start losing steps, then back off by 10%.

Craig