Arc trouble

[Graeme]

When using Turbocnc, my machine runs out of control whenever an arc appears in my G-code. It goes in more or less a straight line to the end of it's travel. The same G-code runs fine under desknc and kcam. Where am I going wrong??
I'm using the Hobby CNC controller and I working in DOS. Thanks in advance for any help you can offer.

[Bubba]

Graeme,
My first question would be, which version of TCNC are you running? If it is prior to V4, there have been known problems with arc generation. Secondly, are you using radius mode or I J mode? It does not do well if you are using R mode and angles approaching 180 or 360.

Could you post the part of the code that is giving you a problem?

[Graeme]

I'm using V3. This is the line in the code where things go crazy.
G03 X2.760254 Y1.581602 I-0.236220 J0.000000
Could my problem be in the G-code converter? I'm using Ace, which boxes should I have checked for the best results?

[Bubba]

Graeme,
The first thing I would do is download the latest version (4.01) and use that as the routines for arc are fixed. download that and then use your existing ini file as a "seed" and it will generate the necessary extras that it has. Save the ini, reset the port and try again.

As far as Ace goes, I haven't used it in a long time and would hate to lead you down the wrong path so I will pass on that one. But you coding looks correct and I assume that you have a preface line to use absolute coding for your G03 and the I and J are set to incremental?

[T-Heli]

HI
I have 4.01 and i need to use G02 or G03 I J mode, if i use R mode

it goes in more or less a straight line to the end of it's travel.

T.J
Sweden

[Graeme]

What is ment by "set to incremental" and "absolute coding" (sorry I'm a complete CNC novice)
I think I must have it in R mode because it will follow an arc if I use a radius in the G-code rather than I and J. I have tried V4 and still have the same problem.

[Bubba]

Graeme,
Absolute means move to a spacific point (eg. X=1.00) whereas incremental movement of X1.00 means move the axis 1 unit from where it is.
So if we start with our tool set at X3Y1, and tell it to G01 X1 (Absolute mode or G90 in our initial setup codes), the tool will move from X=3 to X=1.
Now with the same intitial conditions and if use incremental mode G91 issuing the same G01 X1, will move the tool to X4 (3+1) which is a relative movement from the starting point.
Now back to using I J in your G02 G03 code, you need to go into the configuration setup under RS-274 Dialect and looking at the bottom line where it says "Arc IJK Offsets:" and make sure it says INC. (hopefully shown in the attached picture)
Now for programing the code, I suggest reading either the help file or the manual for further instruction.

Hope this helps

[ger21]

There are 2 different forms of I,J mode. absolute and incremental. Change it under Configure>Rs-247 dialect. It's the last line in that screen.

[Graeme]

Arc IJK offsets are set to incremental, but my router is still running away?

[MIKE JEFFERS]

Graeme
what feed are you running ? on my set up any thing over 150 (mm/min?)
and it gets lazy and takes the shortest route to the end point does it with
angles too slow the feed to 120 (or so ) it's fine . does it in G00 too.
might not be your problem but might help.
mike.