On Thu, Aug 19, 2010 at 10:48:37AM -0500, Viesturs L??cis wrote:

> Ok, but then how comes I do not receive this error, when cutting a
> rectangular hole in material, which is defined by 4 G01 moves (and G41
> or G42 is active) - there is sharp 90 degree corner and round tool -
> so the corner cannot be completely reached. But somehow EMC solves the
> task.

You are right - EMC does have handling for concave corners.  When two
moves come together to form a concave corner, EMC calculates where the
tool is tangent to both original moves and puts the offset corner
there.  The error happens when the tool can't be tangent to both
moves forming the corner because it doesn't fit.

> I am sorry, but I do not really understand, why it is ok for corner,
> where it is turn by 90 degrees, but error is produced, if the corner
> is sharper than 90 degrees. Are there some limitations on how the path
> of the tool is offset, when G41/G42 is activated?

Inside a 90 degree corner is a good simple example: if both moves
making the 90 degree corner are longer than the tool radius, the
tool fits in there.

The disconnect here is you are thinking of a corner as "where I think
a corner should be on my part, even if there are several little moves
in the gcode that the tool can't get in there to touch without gouging
the part" but EMC thinks of a corner as the point where *two* adjacent
moves come together.  EMC handles a corner concavity of *two* adjacent
moves.  EMC does not handle throwing away a whole series of unwanted
moves to make a new corner out of non-adjacent moves.

> > This makes G41/G42 move the path only a tiny amount as if there was
> > a tiny tool. ?Offsetting a tiny amount makes it much less likely
> > that you will have unreachable moves.
> 
> Sorry, but I do not see the difference, I still have to include the
> compensation in the code by CAM programm. I like the ability that I
> can quickly adjust the code by hand rather than doing it in CAM
> application or releasing clamps and repositioning the material on the
> table and then clamping it down again.
> I can still edit it manually, but having the compensation already
> included in the code creates more room for my mistake, so that is why
> I had this question.
> Ok, seems like I will have to live with that.

I think you did not understand what I meant - I wish I could be more
clear.  If the CAM does compensation for the nominal tool size, you
can move the path a little bit by using a small positive or negative
diameter in your tool table.  This will work better.

> Chris, did manage to check the second code sample I provided? Is EMC
> showing error there?

No, I haven't done that.  I'd rather explain the error to you so you
can debug the particulars once you understand it.

Chris

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