Waterline machining proposals

[user1234]

Yes, i have this seen also. Our old CAM program also made G02 and G03. But our new CAM program makes only lines. But the programmer and the machineoperator say that this (or the paths?) is faster ..... . But the memory space, especially for older machines, is a valid point.
Greetings
user

[chrisb]

But the programmer and the machineoperator say that this (or the paths?) is faster

What exactly is it that would be faster, the milling? I guess not, that should in both cases be controlled by feed and distance. The execution of the code? That is probably of no interest nowadays, the limitating factor is the physical milling not the exectuion of the code. Transfer to the machine? Again I guess not, because a tesselated circle with a precision of 1/1000 mm transfers much more data than a single G2/G3 command.

Another argument is reverse engineerig. It is very easy to extract an exact circle or arc from a G2/G3 command compared to doing so from a tesselated path.

[user1234]

Hello!

What exactly is it that would be faster, the milling?

Yes. I have spoken with the programmer today. He said, that all newer programms made short lines. The reason is simple.
First, all new CNC machines have no problem with the memory. Second, when you have a curve, that contains only lines, than you can set for each line a feedrate. So you can build a curve set with G01 + feedrate(X,Y,Z). So machine is much faster, because you can optimize the feedrate. And we do not make serial production and armotized. But we also have no circles in our parts.

Greetings
user

[nahshon]

You may find these links a as useful replacement for slicing a mesh.

• https://www.freecadweb.org/wiki/Part_SectionCross
• https://www.freecadweb.org/wiki/Part_Section

I do not know how to use them internally (from python). I believe there is a way.

* I once used PyCAM that splits a circle (or arc) to multiple line segments. I did not like it from the sound of the steppers...

[chrisb]

I have spoken with the programmer today. He said, that all newer programms made short lines. The reason is simple.
First, all new CNC machines have no problem with the memory. Second, when you have a curve, that contains only lines, than you can set for each line a feedrate. So you can build a curve set with G01 + feedrate(X,Y,Z). So machine is much faster, because you can optimize the feedrate. And we do not make serial production and armotized. But we also have no circles in our parts.

I'm sure there is no significant change in the micrometer range. So why not divide a circle in a far less number of arcs?

[herbk]

Hi,

Second, when you have a curve, that contains only lines, than you can set for each line a feedrate.

I thing that depends strongly from the controller which runs at the machine, and the machine itself.
At a simple "stepper driven" machine (like mine) smal lines would make the process slower in my mind. The reason is: for each direction change (also if it's a very little) the machine slows up and down at each end of a line.

That, may be, is different at newer, usual "linear motor driven" machines. At school we have a five axis homag, i can "feed" it with gcode to, but i don't know to what type of code it gets changed internal...
I have some code snippeds from an other 5 axis machine (don't remember which), there are no G command at it, - just N commands:

Code: Select all

N2 ;Werkzeugtabelle
;T20  103 HM Schlicht D15.25 NL55D1 F2500
;T11  130 HM D20 NL93 (Kugelkopf)D1 F5000
N4 $P_UIFR[1]=CTRANS(X,500,Y,500,Z,500):CFINE(X,0,Y,0,Z,0)
N6 ;Beginn des Hauptprogrammes
N8 G54 M51
N10 G64 G451 CFIN CUT2DF SOFT ;Verschleifen
N12 G153 G90 G0 D0 X600 Z910
N14 G153 B0 C0
N16 ROT X0 Y0 Z0 ;Koordinatensystem zuruecksetzen
N18 ;Block 1 - Schruppen 3D - Z-konstant T103
N20 TRAFAUS ;Orientierung AUS
N22 WECHSEL(20,3,18000,0,0) ;103 HM Schlicht D15.25 NL55
N24 TRAFAN ;Orientierung EIN
N26 F2500
N28 COMPCAD
N30 G0 X202.07 Y115.504
N32 Z142 D1
N34 G3 X205.162 Y124.9 Z135 I2.242 J4.469 TURN=2
N36 G1 X213.938 Y125.7
N38 X214.838 Y125.9
N40 X222.637 Y128.025
N42 X223.588 Y128.4
N44 X231.162 Y131.825
N46 X231.963 Y132.25
N48 X233.825 Y133.438
N50 X240.825 Y138.888
N52 X243.938 Y141.95
N54 X244.463 Y142.55
N56 X249.488 Y148.975
N58 X250.137 Y149.925
N60 X250.937 Y151.2
N62 X251.413 Y152.15
N64 X254.937 Y159.9
N66 X255.237 Y160.8
N68 X257.388 Y168.7
N70 X257.513 Y169.35
N72 X258.288 Y177.75
N74 X258.3 Y178.488
N76 X257.55 Y186.813
N78 X257.325 Y187.988
N80 X255.15 Y195.913
N82 X254.85 Y196.713
N84 X251.15 Y204.813
N86 X250.625 Y205.713
N88 X249.575 Y207.313
N90 X244.438 Y213.875
N92 X243.938 Y214.45
N94 X240.75 Y217.613

I think it's possible to crate a "semi circle" with very short edges with FC. If i have this, Path should create gcode with only G1 commads also... I'l try next time i have to cut out some discs with which code ny machine works faster

[herbk]

I think it's possible to crate a "semi circle" with very short edges with FC. If

It's not...: If i create a regular poligon with 200mm diameter and 300 corners, i get a path with only G1 commands, but if i increase the corners to 600, i get a path with G3 commands.

[GeneFC]

I think we need to keep in mind that FreeCAD is completely standalone with respect to machine tools.

Lots of optimizations are possible for high-end machines with tightly integrated control and CAM functions.

For us little guys using linuxcnc or grbl, or . . ., losing G02/G03 would lead to an explosion of code with zero benefit. Actually, there would likely be a large negative impact, since the optimizations in the controller trajectory planner would be lost.

It could be a feature request to optionally output only G01-type codes, or perhaps a custom postprocessor could be written. (There may already be a postprocessor that outputs only G01, but I don't know which one.)

Gene

[nahshon]

I think it's possible to crate a "semi circle" with very short edges with FC. If

It's not...: If i create a regular poligon with 200mm diameter and 300 corners, i get a path with only G1 commands, but if i increase the corners to 600, i get a path with G3 commands.

Could anyone direct me to the code that's doing it, please?
And I would also like to know where curves get converted to lines/arcs...

Thanks!
-- Itai

[chrisb]

If it is really of benefit to someone a G01 postprocessor is not difficult. I do already some conversion regarding the center of circles.