On 2/8/22 08:43, Les Newell wrote:
One problem is that the arc center has to be calculated based on the
start and end points. Generally we round the g-code coordinates to 3
or 4 decimal places so there is often a tiny rounding error in these
points. In most cases the error is very small and can be ignored. The
big issue is when you have an arc that is nearly a circle. Now any
error on the start and end points is massively magnified by the arc
center calculations. It's a bit of an edge case but if you get caught
by it, the results can be ugly. This is not a fault of the code, it is
simply the way the geometry works. You cannot specify a circle using R
instead of I,J. In this case there is not enough information to even
attempt to guess at the arc center.
Another issue occurs at 180 degrees. Again due to rounding errors it
is possible for the distance between the start and end points is
slightly more than twice the arc radius. In that case the radius need
to be fudged a little to get the arc to fit.
Some CAM packages have an option to break up big arcs to avoid these
problems.
I wondered why the HSM Works post processor generates semi circles
instead of full circles. I don't see an option to break arcs down
smaller. They have a lengthy manual on their post processors that I may
delve into later. So far other than the tool table offset issue, we have
not had a problem with arcs. But then these are high school kids making
their robots, not parts for NASA. :)
Les
On 08/02/2022 01:53, dave engvall wrote:
Hi,
I've read the assertion many times that ijk is better than radius and
always assumed it to be correct; but by how much.
Few of us run machines and are 'new' tigjht ;-) Maybe I've not
looked in the right place(s)
for an analysis or for demonstrated interp of circles with some kind
of error band. Any proof and or experimental evidence?
Just poking the bear. ;-).
Dave
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