Problem with arcs/corners

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sockles
Posts: 2
Joined: Thu Aug 07, 2014 10:32 pm

Problem with arcs/corners

Post by sockles » Thu Aug 07, 2014 10:44 pm

Pictures show the problem. Seems like arcs or corners cause this problem.
Would the paid versions take care of this?

*click the picture to see the tool path, not sure why it didnt shrink the pic instead.

I've also uploaded the gcode


Original code
Image

Autolevelled code
Image
Attachments
top.Part1.nc
(29.48 KiB) Downloaded 54 times

kvnrydberg
Posts: 19
Joined: Thu Jul 17, 2014 4:46 am

Re: Problem with arcs/corners

Post by kvnrydberg » Thu Aug 07, 2014 10:58 pm

What version are you using? Versions before 0.8.3 don't support arcs (G2 and G3 commands) in the g-code. In my experience, the earlier versions work ok for smallish arcs but show the same symptoms as you've got there on bigger arcs. If you're using an old version, you could break your arcs up into smaller smaller arcs in the g-code, or use a CAM post-processor that converts arcs to lines (though your corners would be rougher). Or you could shell out some dough for the newest version. It was money well spent for me.

daedelus
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Re: Problem with arcs/corners

Post by daedelus » Fri Aug 08, 2014 3:54 pm

Just to add to this. I just ran the gcode through AL v0.8.3 and opened the result in CamBam.

In 0.8.0+ the user has the option of using a raw probe file (RPF) which keeps the probing separate from the etching (this has many benefits).

Using the RPF in the AL v0.8.3 process, CamBam shows me this:
083ALwithprobefile.PNG
083ALwithprobefile.PNG (55.78 KiB) Viewed 1331 times
so yes, it looks good to me.

However, if I try again without using the RPF, I get this:
083ALwithoutprobefile.PNG
083ALwithoutprobefile.PNG (59.92 KiB) Viewed 1331 times
As you can see, the Arcs are missing, which is confusing since the Arcs exist in the gcode file. So why doesnt cambam display them?

After much head scratching I came to the conclusion that arc radius' need to be very very precise with respect to the centre of the Arc (defined by I and J) and the start / end points of the arc, otherwise your controller will complain. Cambam probably encountered the same issue and decided not to display any arcs here. Mach3 may or may not have the same problem because each controller has different tolerances with respect to arcs.

So, to answer your question of whether the latest version of AL will handle arcs. YES, absolutely, as long as the RPF is used, see "Probe log levelling (as of version 0.8)" in http://www.autoleveller.co.uk/autoleveller-guide/ for details on how to use this.

When AL encounters a large arc, it breaks it down into smaller arcs using a lot of maths and trigonometry etc. This is a quite complex approach and quite problematic as shown here and in other places on the forum but does keep the curves very smooth.

Probably a better approach would be for AL to convert arcs to lines internally as a post-processor might do and as kvnrydberg mentioned. Once the arcs are converted to lines, AL can just level these, the same as any other line segment. Much simpler.
http://www.autoleveller.co.uk/. Software to probe and adjust a GCode file for PCB's or any probe-able surface.

http://www.autoleveller.co.uk/cnc-probe-guide/. A short guide to setting up the probe.

-James

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