# Machsupport Forum

## Mach Discussion => General Mach Discussion => Topic started by: D-M on June 18, 2013, 09:08:20 AM

Title: radius to end of arc differs from start
Post by: D-M on June 18, 2013, 09:08:20 AM
I need some help please, I posted this on Cam Bam and am having no luck it is a zip line trolley plate nothing complicated an out side cut on a 1/4 plate with some radius  Mach get 's about 1/2 way and stops and I get this message "radius to end of arc differs from start"
Thanks
Dave
Title: Re: radius to end of arc differs from start
Post by: Hood on June 18, 2013, 10:21:58 AM
Possibly the wrong IJ mode, your code should ideally have a G90.1 or G91.1 at the start to tell Mach which mode the arcs are, ie incremental or absolute.
You could go to General Config and change the IJ mode then regenerate the toolpath and see if it helps.
Hood
Title: Re: radius to end of arc differs from start
Post by: D-M on June 18, 2013, 08:16:56 PM
Thanks Hood
so G90.1 is Incremental and G91.1 Absolute or vise virsa? and could you explain a bit about how this is interpreted by Mach I need a better understanding. I know in Can Bam there is a setting for this and I have never understood I down loaded the new version of Cam Bam and now there are a lot of choices.
Thanks Dave
Title: Re: radius to end of arc differs from start
Post by: ger21 on June 18, 2013, 08:33:01 PM
G90.1 is absolute IJ mode, and G91.1 is Incremental IJ mode.

In absolute IJ mode, the I and J values are the X and Y coordinates of the arc center point.
In Incremental IJ mode, the I and J values are relative to the X and Y coordinates of the previous line of g-code.

Whatever method you choose to have CamBam write, you need to let Mach3 know so it knows where the center is.
Title: Re: radius to end of arc differs from start
Post by: D-M on June 18, 2013, 09:02:58 PM
Thanks Gerry
That makes things clear I can see having Mach and Cam Bam butting heads if one is absolute and one is Incremental I will have to go back through my threads on Cam Bam and see what the setting was. Will one cut differently that the other?
Thanks again for the explanation
Dave
Title: Re: radius to end of arc differs from start
Post by: RICH on June 19, 2013, 07:27:20 AM
Dave,
From Help topic in Cambam. I recently updated but didn't have a look at the changes done in the latest version.
Never ends does it...... ;)

Arc Center Mode
This property controls whether the I and J parameters for arc moves (G2, G3) use absolute coordinates or incremental, relative to the arc end points. If this setting is different to the way the CNC controller interprets arc moves, the resulting toolpath may look a mess of random arcs in the controller.
Default When default is set in the drawing's machining properties, the post processor Arc Center Mode will be used. A default value in the post processor will use Incremental (C-P1).
Absolute I & J are absolute coordinates of the arc center point.
Incremental (C-P1) I & J are coordinates of the arc center, offset from the first arc point. This is the typical incremental mode. In previous versions this option was just called Incremental.
Incremental (P1-C) I & J are offsets of the first arc point from the arc center.
Incremental (C-P2) I & J are arc center offsets from the second arc point.
Incremental (P2-C) I & J are offsets of the second arc point from the arc center
Title: Re: radius to end of arc differs from start
Post by: Don C on June 19, 2013, 09:21:33 PM
Ger, what is the differents between a g91 and g91.1. In the mach3 arc pp in aspire it writes a g90 and a g91.1.
Thanks don Clifton
Title: Re: radius to end of arc differs from start
Post by: ger21 on June 19, 2013, 09:41:30 PM
G91 is incremental distance mode and G91.1 is Incremental IJ mode.

G90 is absolute distance mode.

G90 and G91.1 are by far the most commonly used modes.
Title: Re: radius to end of arc differs from start
Post by: D-M on June 21, 2013, 11:16:16 PM
FYI found a good that the CNC cook book has some more good info on this and other mystery's LOL
Thanks for every ones help problem solved  zip line trolley built
http://www.cnccookbook.com/CCCNCGCodeArcsG02G03.htm
Dave
Title: Re: radius to end of arc differs from start
Post by: Chaoticone on June 22, 2013, 12:00:59 AM
Another excellent resource is the CNC Programming Handbook by Peter Smid, 3rd edition.  Also, if your running the default Mach screen on the program run page close to the reset button there are 2 buttons, G code and M code.  If you click on those they will give you a brief description.  Clicking on the G codes will expand on those a little.

Brett