Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: TerryS on January 30, 2022, 09:08:52 AM

Title: Can't cut internal circles
Post by: TerryS on January 30, 2022, 09:08:52 AM

I have just upgraded to a Chinese router after using a Sherline mill that I converted to cnc 20 odd years ago with a Compucut controller. I only used it to cut flat plate ally or pcb board so nothing special was needed. All of my G-code was very simple with only G0, G1, G2 and G3 used. No tool offsets were used as I added in the offset when drawing the part in AutoCad.
Now I find none of the code is usable as it shows all jumbled up on the Mach3 screen although it shows up correctly in BackPlot Editor.
I decided to move forward by upgrading my G-code to be compatible with Mach3 but I have fallen on the first hurdle as I can't even cut a 6mm hole with a 4mm tool. For some reason it wants to cut to the outside all the time so the holes are far too big. I tried using G41 and G42 but one cuts the same and the other crashes the program and it stops in the middle.
Can anyone help with the code to cut a 6mm hole with a 4mm tool?

Thanks for reading

Title: Re: Can't cut internal circles
Post by: JohnHaine on January 30, 2022, 12:23:17 PM

Please post the code which didn't work

Title: Re: Can't cut internal circles
Post by: Graham Waterworth on January 30, 2022, 12:31:37 PM

If working at X0 Y0 and Z0 on top of work then the code would look like this :-


(6MM HOLE USING 4MM CUTTER)
G00 G90 X0 Y0 Z1. S20000 M3
G01 Z-1. F50.
X1.
G03 I-1.
G00 X0 Z1.
M30

Title: Re: Can't cut internal circles
Post by: TerryS on January 30, 2022, 12:54:07 PM

Thanks for your reply Graham, I have just tried that code and it cut a perfect 8mm hole. Is there a setting in Mach3 that could be wrong?

Title: Re: Can't cut internal circles
Post by: JohnHaine on January 30, 2022, 01:39:10 PM

Maybe your steps per unit setting in config motor tuning is wrong, at least for X and Y axes?

Title: Re: Can't cut internal circles
Post by: TerryS on January 30, 2022, 02:23:21 PM

No, I just cut a square and its spot on!

Title: Re: Can't cut internal circles
Post by: BR549 on January 30, 2022, 08:16:50 PM

Check your IJ mode is it inc or abs ?? One will draw it perfect the other will scramble the code.

(;-) TP

Title: Re: Can't cut internal circles
Post by: Graham Waterworth on January 31, 2022, 07:10:25 AM

How can the square be right and the circle be wrong, how did you program the square?

Title: Re: Can't cut internal circles
Post by: TerryS on January 31, 2022, 01:19:20 PM

BR549 you have cracked it! Thanks so much it was driving me mad, I changed the IJ mode to Inc and all is well, a perfect 6mm hole  :D