New Mach3 user looking for some help

[rlink]

Perhaps someone can point me in the right direction. I am a new Mach3 user. I have a 3 axes router from Camaster with a 48x48 table running Mach3. The router is new and I'm trying to cut my first part. I've created a curved part in Aspire and saved both pocket and profile toolpaths using the Mach3 PP for my machine. I've referenced x, y to the front left corner of the machine consistent with how I set things up in Aspire. I've also set the Z to an arbitrarily high height to perform an "air cut."

When I do this, the start of the G-code file runs correctly until it reaches a G3 command, at which point the gantry slows and wanders off until it hits the X limit switch. As far as I can tell, this makes no sense but I don't know jack at this point. It is, however, pretty frustrating.

Here's an example of the start of the G-code file for the profile (or cutout) toolpath using a .25 end mill:

( Cutout 2 )
( File created: Saturday, October 23, 2010 - 04:47 PM)
( for Stinger with Mach 3 from CAMaster CNC )
( Material Size)
( X= 43.000, Y= 43.000, Z= 0.750)
(Notes for Job: )
()
(Toolpaths used in this file
(Cutout 2)
(Tools used in this file: )
(1 = End Mill {0.25 inch})
N110G00G20G17G90G40G49G80
N120M03 G4 4
N130X0.0000Y0.0000F100.0
N140G00X1.5877Y1.9671Z0.2000
N150G1Z-0.1258F30.0
N160G1X3.8377F100.0
N170G3X3.9627Y2.0921I0.0000J0.1250 <- Here's the problem line
N180G1Y2.6858
N190G1X5.9627
N200G1Y2.0921

Works fine until line N170 when it does its wander off into infinity trick at slow speed. It does this, by the way, for three different files cutting radically different shapes from different start positions, etc. As far as I can interpret the code, this line:

"N170 G3 X3.9627 Y2.0921 I0.0000 J0.1250" simply tells the router to travel in a counterclockwise arc from its current position to X3.9627 Y2.0921 with no I offset and with a J offset of 0.1250. I don't see how this can possibly cause the router to drift off into oblivion at markedly slow feed rate and hit the limit switch.

Mach3 is set up the way it was shipped to me. I don't have the slightest idea how to troubleshoot this. This seems like pretty plain vanilla G-code that the router should be able to handle without problems. I am at a loss...

Can anyone get me on the right track?

Richard

[Hood]

Do the DROs and toolpath show this movement or do they show what it should be doing?

Hood

[rlink]

Yes. The DROs and the toolpath shows the strange motion. In addition, after I hit stop I can send the machine back to zero by selecting "go to zero" so things remain referenced properly.

Richard

[Hood]

Ok so when you first load the code does the toolpath look correct?
If it has a big arc where it should be a small arc then go to General Config page and change the IJ mode.
Hood

[rlink]

Thanks a ton for the help. I switched to IJ incremental mode and this seems to have improved the problem. Not sure why it should be on incremental rather than absolute. At least it seems to do better in an air cut. I'll post an update once I see how it actually works when cutting the material.

Richard

[ger21]

Not sure why it should be on incremental rather than absolute.
Richard

Because that's how Aspire writes it's code, in Incremental IJ format. This is probably the most common question from beginners, usually asked about twice a week here.

[rlink]

Ah. Sorry about that then. I guess I could have found my answer by more diligent searching. Even so, I really appreciate the help and it made a big difference in my progress.

Richard

[ger21]

No problem. I think the default IJ mode in Mach3 is absolute, but incremental is the most commonly output format from most CAM programs.

And I personally have never had a lot of luck with the search function here, either. so being more diligent is no guarantee.

[Greolt]

Richard I am interested in how this happened to you as an Aspire user.

What PP are you using?  Are you using the latest version?

The Mach PP outputs a G91.1 command in the header, which sets arcs to incremental.

Greg