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Author Topic: feed per rev versus feed per minute  (Read 950 times)

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feed per rev versus feed per minute
« on: February 08, 2019, 07:48:15 AM »
Hello Chaps
I am using mach3 turn and mainly turning plastic
I have initialized the code to g21 which call for feed per revolution.
I am finding that during the program the feedrate changes of it own accord.
I set the feed at F0.5. but when running the feed fluctuates between 0.2 and as
high as 1.5
I am on windows 10 with a 64 bit machine - can anyone offer a reason?
in the meantime I am going to be using feed per minute to see if it gives
many thanks


think of the trees-- use both sides of the computer paper

Offline RICH

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Re: feed per rev versus feed per minute
« Reply #1 on: February 09, 2019, 08:58:58 AM »
Make sure you are in the right mode ie; G94 or G95.

How close is your Kernal speed as compared to selected kernal speed in configuration?
- When you run the driver test in Mach3 it will show actual your actual Kernal Speed.
   Some users have a kernal speed indication via a pulse frequency DRO on the diagnostics screen.
   The closer the actual kernal speed to selected kernal the better.
- RPM is real time but there is a lag in what the DRO shows.
  The rpm should not fluctuate, maybe 1 or  2  rpm, but, if the rpm varies the feedrate will vary.
  You should check your actual rpm......Mach3 rpm indication is more accurate than a lot of rpm indicators!

The above is for Mach 3, but I don't use Win 10 / 64 bit,  and don't know what version you are using, so
can't speak for that system.

BTW, There is a big difference in a visual movement of the axis for an feedrate between .2 and 1.5.
           Try G1 Z...... F ( value .01 to 1.5 ) to realy get a visual flavor of actual movement.
           You would plainly see it. Mach tries to maintain feedrate via rpm sampling.

Re: feed per rev versus feed per minute
« Reply #2 on: February 10, 2019, 11:10:30 AM »
Thanks Rich- I will chaeck this out when I am back at the machine
I have checked the rpm with an accurate rpm meter ( An old English
automotive type) and found that the RPM is spot on regarding what
Mach 3 is reporting . Also - Sorry I made a mistake - the computer
is not windows 10 nor 64 bit ( My mistake ) I will give you better
info tomorrow when I an back at the machine. I have noticed that the
RPM shown does vary and will report back on that as well
One thing about the driver test - when I run the driver test the graph
shows a lot of noise - continual peaks close together - but it still reports
system excellent so I havent concerned myself with that.
The feedrate variation is very noticable on the coarsness of the cut when
doing a longish cut ( say 150mm along the od)
thanks for your input _ i will report back again in a few days
think of the trees-- use both sides of the computer paper