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Author Topic: Tuning Counts per Unit  (Read 400 times)

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Tuning Counts per Unit
« on: December 23, 2018, 05:14:59 PM »
Hi all,

Im having some trouble getting my Counts / unit set right.  Ive calculated it at 940.8222. 
  My first question, is:  are the numbers after the decimal point used?
Second:  Ive made some test cuts and on two cuts 40" apart the actual cut is 40.125"  Ive tried with and without cutter compensation.  No Change.  I brought the counts per unit back to 937.*********  and the cut was right but when I post process a fusion part it show up .375" shorter on  a 40" cut  I can duplicate this in x an y axis.  Any Clue why id lose some length just using Fusion?

Re: Tuning Counts per Unit
« Reply #1 on: December 23, 2018, 05:39:57 PM »
my understanding is that Mach uses the decimal numbers including the fractional part in its calculations but the trajectory data
dispatched to the motion controller is integer.

To use your example if you called a move of 10 units mach would calculate 9408.222 steps are required but would issue the integer
amount 9408 steps to the motion controller.

I'm not sure whats going on with Fusion.

The single most important point is that if you issue a move of 40 inches your machine MUST move 40 inches, not 40.1 or 39.9 but 40.00.

I suspect that either Fusion or Mach or both is making tool diameter allowances which describe the difference.

I go back to the above, tune Mach so that a command of 40 inches causes the machine to move 40 inches. Once you have found that 'steps per'
number LEAVE IT ALONE. It will stay fixed for the life of the machine. All other variances are to do with either Machs Gcode interpretation and/or
your CAM program. You will have to sift through until you find the discrepancy but leave the 'steps per' alone.

My wife left with my best friend...
     and I miss him!
Re: Tuning Counts per Unit
« Reply #2 on: December 23, 2018, 06:02:08 PM »
If you are going to use cutter comp in Mach4 be sure that you set the "Compensation Type" in Fusion, in the Passes Tab on an operation to "In Control".
Chad Byrd
Re: Tuning Counts per Unit
« Reply #3 on: December 23, 2018, 10:21:26 PM »
when you say you are moving 40 inches...how are you doing it? I presumed, perhaps mistakenly an MDI move like G0 X40.
It may pay to issue a G40 (cancel cutter radius compensation) prior to your move just to be sure that Mach is not doing anything weird.

If you enter an MDI move then Fusion is not even part of the equation.

My wife left with my best friend...
     and I miss him!

Offline Stuart

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Re: Tuning Counts per Unit
« Reply #4 on: December 24, 2018, 03:56:24 AM »
First thing is the mach4 post from fusion is wrong for cutter comp

Both d and p are valid for mach4 but
The post uses p and all it does is to divide the cutter dia by 0.5 hence NBG

You need to modifiythe post to use D correctly ie. change the p *********xx to d *********xx

It’s a few lines to give you the pos and neg cutter comp

Have a look at the Fanuc post do a look up for the d******************

due to this stupid forum software rename the file to mach4.cps.  and store in your personal post folder
I wil try top post again  >:D

I have a modded post that works I will upload when I am on the desktop
« Last Edit: December 24, 2018, 04:07:32 AM by Stuart »