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feed rate changing during machining
« on: March 29, 2015, 11:27:49 AM »
Hello Chaps-
I am trying to learn gcode - please help

Below is a piece of code that I am practising my coding with
the plan is to bore a hole of 11.5mm out to 14.4 mm
Excuse all the remarks- they are just for my own reference

The feed is set to 0.1 mm per rev
A parameter called #1 contains the current cut size and is incremented each cut
at completion of each cut the tool backs off  ,  moves to z home then back
to the x size that it was before backing out. ( this sets the DRO to
the size of the cut just taken so i can see what the size should be)
the spindle stops and the feed pauses so that i can check the size of the part.
I then press "cycle start" and it caries on again.

Note that feed is set to f0.1 mm per rev
But the feed changes of its own accord ( apparently at random downwards)
so that when i press "cycle start " again the feed is now .01  ??

can any of you tell me why it is doing this??
 







% filename is    :-   simple boresinglecut.tap
% program number:-   01001  (program number -put at start of program)   
% Program name    :-   simple boresinglecut.tap
% Program description:-   Makes a single cut in the bore according to parms set
% ----------SETUP STRING (INITIALIZATION)------
m05            (stop the spindle)
g18g21g40g49g61G80g95S1200
%g64            (constant velocity mode)
f0.1
g28
#1=11.5         (bore start dia)
m3            (start spindle forwards)
% start position
f0.1         ( feed o.1 mm per rev)
g0 z19         (start to clear front of boring bar)
g0 x#1         (START POSITION)
g0 z0.5         (move z closer)
g01 z-21      (bore to size)
g0 x[#1-0.5]z-20(backs off)
g53g0z0         (use machine coords to go to z home)
m05            (stop spindle)
g0x#1         (put tool back to show size on dro)
m00          (msg,stop and measure)
m3
#1=[#1+0.5]      (reset diameter parm)
% start position
f0.1         (feed 0.1 mm per rev)
g0 z19         (start to clear front of boring bar)
g0 x#1         (START POSITION)
g0 z0.5         (move z closer)
g01 z-21      (bore to size)
g0 x[#1-0.5]z-20   (backs off)
m05            (stop spindle)
g53g0z0         (use machine coords to go to z home)
m00          (msg,stop and measure)
m3
#1=[#1+0.5]      (reset diameter parm)
g0 z19         (start to clear front of boring bar)
g0 x#1         (START POSITION)
g0 z0.5         (move z closer)
g01 z-21      (bore to size)
g0 x[#1-0.5]z-20   (backs off)
m05            (stop spindle)
g28            (return home)
m00          (msg,stop and measure)
m3
#1=[#1+0.5]      (reset diameter parm)
g0 z19         (start to clear front of boring bar)
g0 x#1         (START POSITION)
g0 z0.5         (move z closer)
g01 z-21      (bore to size)
g0 x[#1-0.5]z-20   (backs off)
m05            (stop spindle)
g28            (return home)
m00          (msg,stop and measure)
m3
#1=[#1+0.5]      (reset diameter parm)














think of the trees-- use both sides of the computer paper
Re: feed rate changing during machining
« Reply #1 on: March 29, 2015, 01:11:14 PM »
I'm not code savvy enough to follow what you've posted but I had similar issues using G95.  They were caused by (I think) Mach "sampling" the spindle speed while it was still on the way up from stop, ie: not yet up to full speed and the feed rate would be wierdly random.  Putting a 2 second pause in my spindle setup options fixed it for me.  Dunno if that's the problem or the correct way to fix it but it worked.  This stuff is still black magic to me!
Milton from Tennessee ya'll.
Re: feed rate changing during machining
« Reply #2 on: March 30, 2015, 07:01:21 AM »
Thank you I will try this tonight
regards from south asfrica to tennesee
fred
think of the trees-- use both sides of the computer paper