Re: Absolute vs Incremental 3D programming

Gary H. Lucas wrote:
"Bart" <bborb@fusedotnet> wrote in message
news:e4b46$440cc7c9$d8444263$27634@xxxxxxxxxxx

"Black Dragon" <bd@xxxxxxxxxxxxxx> wrote in message
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Seeing how we're not far from taking delivery of a machine with a
Fanuc 18i control for which we do not have a post processor which
means I'm in the process of tweaking a stock generic Fanuc post,
I'm wondering if there is speed advantage or otherwise using
incremental positioning vs absolute for 3D mold/die type work? I've
never posted 3D tool paths in anything but absolute, but have done
manual programming in incremental.

If it's a wash, I'll be giving incremental a try anyway. In that
case, is there anything that might bite me in the ass that I should
be looking for while debugging a post?

--
Black Dragon

Balls Law:
The angle of the dangle is directly proportional to the heat
of the meat provided that the thrusts of the busts are constant

Old toolmakers like myself remember before we had digital readouts,
nothing but an incremented dial at the base of the handles we
cranked (all day). If you remember this, you KNOW backlash doesn't
accumulate. If you have .015in backlash and you bring your edge
finder into the side of the part, set the dial and move half the
edge finder and reset the dial to zero, you can crank anywhere on
the table as many times as you want all day long and the largest
deviation from zero will still be in the .015in window. I'm ONLY
speaking of backlash, not pitch error (which is accumulative) or
squareness of ways, etc.
I'll also mention that the CNC control does math in AT LEAST six
place decimal and that math remains used in the background, it is
always accurate to at least the six places regardless whats
displayed on your four place decimal screen, so there would have to
be a ton of rounding before it affected the displayed four place
decimal we erroneously assume is the final result of the math.
Motion is determined in revolutions, a single revolution being an
exact number, so rounding errors are contained in just that window
(usually maybe .200in or maybe a metric amount per rev), so a long
move is thought of as "how many revs, then the closest part of a rev
(closest part of the rev being the only place rounding occurs, and
its a six place decimal or more). All math is done from machine
zero, no matter how many work zeros you use.
You can bounce back and forth between incremental and absolute as
often as you please, it doesn't affect accuracy. Absolute is user
friendly after we mark up the blueprint and start programming, I
used to like putting my incremental sequences in subprograms so if I
needed to move a part of the feature it was a simple one or two
edits, no refiguring ALL the absolute numbers that follow or worse
yet re-camming and re-posting.
Back to the old handle/dial machines, we COULD increase error if we
loosened our dial to set a new zero and weren't careful about the
last direction we moved when we did this. This is not the case with
CNC when you set work zero(s) because all math is done from machine
zero at the startup of the machine.
Just my opinion,
Bart
I find myself in the No additional error camp when using incremental.
However I no longer have access to a CNC machine and this is trivial
to check out on a real machine, so when are one of you guys going to
give us the report?


As soon as Everybody Loves Raymond is over. Unless I fall asleep that is.


--
John R. Carroll
Machining Solution Software, Inc.
Los Angeles San Francisco
www.machiningsolution.com


.

Relevant Pages

  • Re: Absolute vs Incremental 3D programming
    ... 18i control for which we do not have a post processor which means I'm in ... anything but absolute, but have done manual programming in incremental. ... day long and the largest deviation from zero will still be in the .015in ... I'll also mention that the CNC control does math in AT LEAST six place ...
    (alt.machines.cnc)
  • Re: Absolute vs Incremental 3D programming
    ... anything but absolute, but have done manual programming in incremental. ... deviation from zero will still be in the .015in window. ... I'll also mention that the CNC control does math in AT LEAST six place ... All math is done from machine zero, no matter how many work zeros ...
    (alt.machines.cnc)
  • Re: Our greatest problem!
    ... math to be correct. ... limitations by the present day physicists. ... no absolute reference frame is allowed. ... real changes, there must also be real changes in the ...
    (sci.physics.relativity)
  • Re: Our greatest problem!
    ... math to be correct. ... limitations by the present day physicists. ... no absolute reference frame is allowed. ... real changes, there must also be real changes in the ...
    (sci.physics.relativity)
  • Re: Our greatest problem!
    ... math to be correct. ... all things are based upon an absolute reference ... there are real changes in the rates of clocks. ... mechanics conserve total energy. ...
    (sci.physics.relativity)
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