Drilling toolpath optimization Re: New router video..

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@...>
wrote:

> > And seeing as how the machine is being presented as an optimum

and

> > advanced type; it seems likely to me that someone new just might
> > want to copy what they see toolpath-wise. (Why? Cuz that's the

way

> > the experts do it; I saw it on a video... A machinist corollary

to

> > the cut off both ends of the turkey thanksgiving story.)
> >
> > So I mentioned the serpentine and the why; then added the use-
> > fastest-axis-for-longest-move at the end.
> >
> > You might think these things are obvious; but many years of
> > instructing folks new to CNC has shown me that they are not.
> >
> > Ballendo
> >
> >
>
> You did say FYI, there was no way to know it was a plural your i.e.
> "beginners this is FYI".
>
> It might also be argued that despite the fact that the group caters
> for beginners (as well as experts as it happens) there should be no
> pressure for any contributer to try and act as a role model in
> everything they do. The video was to display speed not efficiency

and

> I don't remmember it being touted as an optimum or advanced design
> just a fast and cheap one.
>
> Optimization of tool paths is a really interesting topic and it was
> worthwhile noting that the tool path was not optimal but I can see

why

> conflict might have arisen even if no offence was intended as I am
> sure it wasn't.

Videos are often misleading and can show the special effects that
the filmographer wants. Hopefully in the day of photo realistic
computer animation and cheap desktop pc-video production, that will
not be overlooked by a CNC newbie.

Drilling toolpaths ( indeed any one of a multiple process CNC job)
are often taken out of context of the rest of a CNC job and
the "goal" becomes minimization of the cutting time with no regard
to the most optimal solution for the job at hand.

For a group of folks in the home-built world, achieving programmed
motion is a major accomplishment and their "goal". Beyond that,
other factors of CNC programming and part making don't really
matter, unless they get in the way of making parts for CNC machine
number 2, or 3, or 4, etc. Some even seem to go so far as to
measure their manliness by bragging about theirs being
the "biggest", fastest, longest, etc. There is a lot of shouting
and pushing as the testosterone splashes around. In this group,
CCED, it comes out as passive-aggressive as most of the rest of the
off-topic caterwauling is suppressed.

There is also a very large percentage of people in this group that
see making their own CNC as only a small step toward their goal.
They are more interested in how to leverage their available funds
and components, to make not a working CNC, but rather a useful AND
efficient machine tool.

What is not evident from a video clip of a few simple drilled holes
is how to approach hole drilling, and how to use a Cad-Cam program
to improve things.

Generally speaking the shortest travel distance yields the fastest
G81 to G80 time. The zig-zag mentioned by Ballendo would most
definitly be an improvement over the sub-optimal, down and back that
was shown in the video. The zig-zag may not yield the most optimal
approach if there is a relatively long distance between the start
and end points. What's next after the holes are drilled? Move to
tool change position to change the tool, move to workpiece changing
position to change out the chunk of material? The moves before and
after the drilling cycle may be more significant to the job
efficiency than the drilled holes.

The shortest distance solution may not take into consideration hole
location accuracy. A drilling toolpath that eliminates the effects
of backlash would for instance be preferable if the part required
more precise hole locations. Even in a commercial setting this may
permit accurate processing of a part on a machine with lesser specs.

A G81 "center of grid" start to G80 "center of grid" end
optimization would be better if multiple tools were to be used and
if the tools can be changed over the workpiece.

Assuming that more than one or two parts are required, an even more
dramatic optimization can be easily achieved by eliminating one or
more toolchanges by running, multiple parts simultaneously. It
should be obvious that the first hole of the second part should be
adjacent to the last hole drilled in the previous one, and certainly
not diagonaly at the farthest distence between the two part
extremes. Careful analysis may show that the center to center
toolpath is best, but most likely an optimization of all the holes
in all the parts would yield the most productive solution.

Tool heating would probably not be one of the factors that most
experienced CNC users would consider when developing toolpaths as
tool heating is easily cured by sharp tools, proper feeds and
speeds, and the application of compressed air or mist, or flood
coolant. Those factors are best addressed in the machine design
phase and process planning, not in part programming and production.

Well that sounds like a good start for an article in Digital
Machinist....

Fred Smith - IMService
http://www.cadcamcadcam.com/hobby