Re: NAN Bug with circular moves

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

Ian Wright wrote:

> Hi Will,
>
> I finally got round to compiling in your 'fix' file and playing around with
> the system again. The program you suggested runs fine and has obviously
> sorted out the initial problem, however, being of an adventurous nature I
> seem to have found yet another way of goofing it up! - sorry.
>
> Being still a relative dimwit at this cnc stuff and yet being dazzled by the
> apparent magic with which these things are bestowed, I reasoned that, now
> the tool can be made to describe a complete circle with only such a simple
> command, could it also do something really clever like machine a circular
> spiral - as in producing a snail cam for example. So I stuck a 'z' component
> in and guess what - same problem again and nothing told me I couldn't do it
> before the (virtual) tool ascended into orbit with the 'x' and 'y' axes
> trazzing off at a 45 deg. angle at high speed. Try it - the line I used was
> g2x5y0z1i-5j0 in place of your second line, a simple change but very
> effective!!!  ;o)

Oh, oh!  This is helical interpolation, and is necessary for milling threads.
I have a program that writes RS-274D code that uses this, and it worked
some months ago, last time I used it.  If we have loused up helical
interpolation, then we need to get it fixed.

As for spirals, there is no standard command for that.  There are special
codes used on various controls for spirals, but I wrote a program that
approximates a spiral with circular arcs in quadrants, to open up
a hole in something.  See the makebore program on my web page
 http://www.artsci.wustl.edu/~jmelson/gcode.html .  The first
program is the one that does this.  The sample run repeats the
expanding spiral at two Z levels, and then makes a final, full circular
pass to clean up the bore.

You can extract the spiral generating logic from this program, and
make a few simple adjustments to make it do smaller segments, if
you want to cut real spirals with accurate curves.

Jon