I have been milling a kontour on stainless plate 75x12 (all measures are mm)
It’s been working fine, but when the mill is about to finish the arc, it’s not completly round.
It’s not a problem for anyone but me. Any suggestion to a solution.
My machine is a abene VHF 40 CNC and Heidenhain 155,
I also suspect that the radius compensation is calculating a bit wrong, had to move center 1mm to get the measurement correct.

Could you post the program (g-code)?
What dia. tool are you using?
What is in your offsets for this tool?

Code used Heidenhain plain lauguage programming
Tool def 1 L=0 R=6
Tool Call S=70 (ca. 700 rpm)
L X 500 Y-85 Z 1 F3000
L Z -13 F3000 M13
L X 485 RR F3000
L Y-65,784 RR F100
CC X 495 Y-37,5
C X 485 Y-9,2157 DR- RR F100
L Y 2 RR F100
L X 500 R0 F3000
L Y 50 F3000
the dia. of the tool is 12mm, I'm doing the countour once at full depth.
There's no funny noises, chips looking fine

Your
CC X 495 Y-37,5
is probably not accurite, its supposed to be the coordinates of the center of your circle/arc your trying to achieve.

from the end of the piece to the buttom of the arc, there should be 20 mm, and the radius of the circle is 30mm, so I think the CC is allrigth, but
I had to program it CC X496 Y-37,5 to get the measument ok
The attached file is the drawing

Ah, my bad.
Program looks ok dimension-wise.
For grins and giggles, change R=6 to R=6.5 and cut a fresh piece, then change back to R=6 and recut same piece. This should make your recut a "skim cut" with minimal tool pressure. If you get the same results then the problem isn't in your program.

Thanks for the help and inputs.:) Apreciate any contact, cos I'm CNC department at the shop
I'll try next time to cut it twice using 2 R-values

If it helps, after changing the R6 to R+6 and running it on my Cutviewer programme ( www.cutviewer.co.uk ) the file looks ok. See attached.
Where is it looking wrong?

0 BEGIN PGM 123 MM
1 TOOL DEF 1 L=+0 R=+6
2 TOOL CALL S=70
12 L Z+2,000 R F9999 M08
3 L X 500 Y-85 Z 1 F3000
4 L Z -13 F3000 M13
5 L X 485 RR F3000
6 L Y-65,784 RR F100
7 CC X 495 Y-37,5
8 C X 485 Y-9,2157 DR- RR F100
43609

43610
9 L Y 2 RR F100
10 L X 500 R0 F3000
11 L Y 50 F3000
96 STOP M02
97 END PGM 123 MM

It's just at the end of the arc (about 14-15 degrees before the end), just when the mill is commimg free of material, overlength is 1mm.
I suspect that you'r solution will work out fine
I'll guess my next problem is translation off words off the trade from danish to english *lol*
By the way, how do you get the pictures in the text??

Thanks again
Jens Præst

Good, hope it works.

To get the pictures in the text use attach & upload them first and then click on the file to insert, in this case attach.bmp 43611

Could I use Heidenhain plain launguages in the cutviewer program that you use John??

Yes you can. :)

Guess I'll try the free download for a couple of days then