Gentlemen,
When playing with the machine sim I noticed a protocol that looked
a little unfamiliar. The retract levels looked different than what I
expected. This was in the G83 peck cycle. The g98/g99 commands seem to
work "almost as expected". The description in the EMC2 "G-Code" Quick
Reference seems reversed. It is confusing.
When I say "almost as expected" I mean the end result is correct
but during the cycle the motion looks different. The G98 retract
should cause the machine to retract to the position the machine was in
when the canned cycle was started. It does, but, it also returns to
the start position at every retract during the drill cycle. This is
different than what I see on other controls. On other controls the G83
peck cycle returns to the R point for all peck cycles. The only time
it returns to the start point is when the cycle is done. This allows
the programmer/operator to cause the machine to retract to the start
point (G98) for subsequent xy motion commands or cause the machine to
remain at the R level (G99) for subsequent xy motion commands.
The current EMC treatment is not wrong, just different.
This is out of the RS274NGC language on the EMC website:
3.18.4 G83: Peck Drilling
The G83 cycle (often called peck drilling) is intended for deep
drilling or milling with chip breaking. The retracts in this cycle
clear the hole of chips and cut off any long stringers (which are
common when drilling in aluminum). This cycle takes a Q number which
represents a "delta" increment along the Z-axis. Program G83 X- Y- Z-
A- B- C- R- L- Q-
1. Preliminary motion, as described above.
2. Move the Z-axis only at the current feed rate downward by delta
or to the Z position, whichever is less deep.
3. Rapid back out to the clear_z.
4. Rapid back down to the current hole bottom, backed off a bit.
5. Repeat steps 2, 3, and 4 until the Z position is reached at step 2.
6. Retract the Z-axis at traverse rate to clear Z.
It is an error if:
* the Q number is negative or zero.
Stuart's comments
number 3 - the rapid back out to the clear z is the same whether in g98 or g99
number 4 - I have never liked this statement "backed of a bit". It is
set by a parameter in the control. Some materials and hole sizes
require a different amount of "backed off a bit". When a
programmer/operator begins playing around in the machine setup
parameters there is too much opportunity for disaster. I have always
felt this amount should be an argument on the G83 line.
The fanuc control also has a G73 peck cycle. This cycle doesn't
retract out of the hole, but instead retracts "just a little bit" to
break the chip, then feeds from that point. This is another example of
the "backed off a bit" I have never liked.
I don't know if anyone has any interest in implementing G73 or any
other cycles. It is not a big issue. The only issue I see for general
use is - without the G73 cycle EMC is less compatable with some
existing programs.
thanks
Stuart
-------------------------------------------------------------------------
SF.Net email is sponsored by: The Future of Linux Business White Paper
from Novell. From the desktop to the data center, Linux is going
mainstream. Let it simplify your IT future.
http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
