Re: EMC minor quirk

[Jon Elson <jmelson-at-artsci.wustl.edu>]

Ray Henry wrote:

> Dan B.
>
> Welcome.  You have a good point with tangent lines to an arc.  I seem to
> remember reading that EMC's cutter comp attempts to maintain the same
> feedrate at the point where the tool touches the part regardless of the
> shape of the cut being made.  If you move into the inside of an arc the
> machine speed should slow, if outside it should speed up.
>
> When EMC comes to an outside corner it describes an arc around the corner
> using the hard corner as the center, and the radius of the cutter as the
> path radius.  Then it uses the approach to the corner as tangent offset by
> radius and the line after the corner as tangent offset by radius also.
>
> I don't know if this is what Jon was hearing but a hard 90 sounds pretty
> strange with my steppers.  It's like going around a quarter circle where
> one axis slows and the other accelerates.

No, the programs I saw this in were not doing 'hard 90' turns, but fairly
gradual 90 degree turns with a radius about twice the cutter's radius.
It seemed the arc and the line were run at the same speed, but there was a
VERY short acceleration right at the end of the line.  The lines were
about 4" long, and the acceleraion was along a length of maybe .1 or
.2".  Running at about 10 IPM, it lasted no more than a second.

Jon