Cutting a non-circular arc ?

[greybeard]

If I want to cut a parabolic path, or any non-circular arc, do I need to be able to programme ?
The alternative to writing hundreds of lines of code for small incremental moves would be to either write my own program, , or to be able to tell the machine to run some sort of iterative code that stops after a given number of cycles, then moves on the the next instruction.
Any help, please ?
John

[vlmarshall]

Well, there's no canned cycle that will cut a parabolic arc, but if you can define the arc mathematically, I don't see why you couldn't get EMC to move from point to point along the arc.

Running for a set number of cycles and them moving on, or cutting each cycle with a slightly different path (such as stepping down, or over, or along a radius) is the REASON I switched from Mach3 to EMC. I use conditional loops and program variables constantly at work, and just HAD to have them at home, too.

http://www.linuxcnc.org/docview/html/gcode_main.html

[ger21]

The end result is always a series of short, straight moves. The easiest way to get there is to find a CAD program that'll let you do what you want, and export a .dxf of line segments and convert that to g-code.

Another easy way is to use Excel to output the G-code.

[Pandinus]

Programming the part's surface path isn't so hard... figuring out how to compensate for the shape of your cutter can be fun though
I.E. calculate the path of a vertical circular arc...
x^2+Z^2=R^2
Z=(R^2-X^2)^.5

If your cutter is a sphere, it would come out fine if you just subtract its radius from the final radius, but if your cutter is a cylinder, flat end, like an end mill.... then you need some Trig. to find your cutter compensation... same for a parabola and a round cutter.

[epineh]

Hi John, I had a small program a couple of years ago that created code for mirrors, lenses and I think it would do parabola's as well, I cannot think of its name but if I can dig it up I will let you know.

Cheers.

Russell.

[beege]

If an ellipse is oriented in one of the axes, it would be a one axis scaling thing, which I don't know if EMC has.

[greybeard]

Morning all, and hi Russell.
Welcome to another room in Greybeard's Home for the Bewildered.

My request for this bit of info comes from my other thread on working out a centre line Roman letter plot.
To generate a decent looking serif, the 60 degree v-cutter needs to follow a short parabolic helix, and given the emc doesn't have a gcode for that, it's going to be a series of short cuts, ramping down to the final depth of the main stroke of the letter.

I have no problem with producing the function of the curve, but only have a vague idea on how to write the gcode such that the interpreter will calculate a series of steps for me.
For example, if I needed to cut a sine curve -
X [#1], y[ sin^-1#1] (where #1 goes from 0 to 1 in steps of 0.05 )(Not sure if ^ is the correct symbol for "to the power of")
Then when #1 reaches 1, the plot moves on to the next line of code.
I have some idea that this uses an IF -, THEN -, structure, but I don't know how to set it out.
Regards
John

[epineh]

Hmmm... V-Carve would do this pretty easily

Russell.

[greybeard]

If I had a dog, I wouldn't have to bark
John

[vlmarshall]

Morning all, and hi Russell.
Welcome to another room in Greybeard's Home for the Bewildered.

My request for this bit of info comes from my other thread on working out a centre line Roman letter plot.
To generate a decent looking serif, the 60 degree v-cutter needs to follow a short parabolic helix, and given the emc doesn't have a gcode for that, it's going to be a series of short cuts, ramping down to the final depth of the main stroke of the letter.

I have no problem with producing the function of the curve, but only have a vague idea on how to write the gcode such that the interpreter will calculate a series of steps for me.
For example, if I needed to cut a sine curve -
X [#1], y[ sin^-1#1] (where #1 goes from 0 to 1 in steps of 0.05 )(Not sure if ^ is the correct symbol for "to the power of")
Then when #1 reaches 1, the plot moves on to the next line of code.
I have some idea that this uses an IF -, THEN -, structure, but I don't know how to set it out.
Regards
John

Something like:

O100 While [#1 LE 1]
G1 X [#1], Y[ SIN^-1#1]
#1=[#1+.05]
O100 ENDWHILE

...but the [sin^-1] doesn't work.

[greybeard]

Something like:

O100 While [#1 LE 1]
G1 X [#1], Y[ SIN^-1#1]
#1=[#1+.05]
O100 ENDWHILE

...but the [sin^-1] doesn't work.

Thanks for your help vlmarshal.
My [sin^-1 *#1] was a complete guess as to how to express
"that number which was the sine of n degrees, where n went from 0 degrees to 90 degrees in 20 steps".
I think it should have read Y[SIN[**-1]#1], but I see it wouldn't have worked anyway.

I'll see what I can learn about the WHILE/ENDWHILE command, but I may come back for more help.

Regards
John

[greybeard]

Is there a list of O-codes showing specific meaning associated with particular numbers, or does the operator define their own meaning ?