I am using Mach3 (licensed, for sure) with a T-Tech PCB milling machine and a homebrew controller.

The T-Tech is basically a 12" x 12" x 1" milling machine, with steppers and ball screws.  VERY precise, certainly capable of milling within .001".

I create my PCB in the editor, export the geometry as Gerber files, then convert the Gerber to GCode using FlatCAM.  I mount a piece of PCB with double-sided tape, install a .015" endmill and start "isolating" traces.

The whole setup has worked fine for years; I've made dozens and dozens of little (and not so little) circuit boards.   Worked fine until recently, that is, when it's started to do something weird.

It's most obvious when asked to mill a circular path, say, for a mounting hole.  Rather than milling the whole 360 degrees, it only mills about 350 degrees.  In fact, just about every path ends a wee bit short.

The fix is to place the "finished" board under a microscope with a sharp knife and scratch out the last few thou of copper from just about every trace.  Crazy.

It seems worse when doing arcs, although this could be my imagination; just about every outline has an arc in it, and FlatCAM always starts on a curve.

And FlatCAM doesn't actually do arcs (G02/G03)  Rather, it does zillions of short segments.
 
Attached is a bit of GCode created by FlatCAM to cut (outline) a single circle. 

This code seems to simulate properly, and just looking at the code, circles do end where they start.

And I don't think it's missing steps, because the boards always come out fine, save for these uncut bits here and there.

My best guess is that the machine is starting the horizontal motion before cutter is fully down, before the vertical motion is complete.

Is it POSSIBLE that there's something weird going on in Mach3?  Some setting I've inadvertently changed?

Thanks for any thoughts.



Alan

Bad form to reply to my own post, I know, but I have a bit more info.

If I manually add a delay to each Z down, the problem goes away.

That is, if

  G01 Z-0.0300

becomes

  G01 Z-0.0300
   G4 P.03

the paths are cut completely.  I have no idea why this is happening, but it's completely repeatable.

I SUPPOSE I can post process my GCode through a text editor, but it's really not supposed to work this way ...

Just out of curiosity & as a test, try changing from Constant Velocity to Exact Stop mode (Config. / General Config.). Does this resolve the problem ?

Thanks, I'll give that a try!