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Author Topic: Mach 3 CNC cutting 1/32" too far in both X and Y axis  (Read 1849 times)

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Mach 3 CNC cutting 1/32" too far in both X and Y axis
« on: November 10, 2014, 03:16:02 PM »
Hey everyone.

My old XP computer died out on me the other day and I had to upgrade to a new one running Windows 7, 32 bit.

Back story:
I run a lot of the same parts on my spoil board. It is filled with indexing pins and bolts to attach guitar blanks. I am using my CNCs home position as my work zero. I just bring the Z axis down to locate where the top of the wood is and set it. All my programs are made with the home zero of the machine being the location point. It has worked many times before switching to this new computer.  My machine calibrates by moving to it's home position (X0, Y0, Z0) and hitting a couple of limit switches. This is what tells it where it is.


The problem:
Today I noticed the Y axis and X axis cut almost 1/32" too far (equally). I could tell this because I could see new cut marks in my spoil board. This spoil board has many old cuts in it from running the same guitar neck from the old computer. Taking measurements from an old guitar neck and comparing it to the newly cut one shows everything off 1/32" on one side of the new guitar neck.


I have no clue why this is happening.

Any suggestions?
Re: Mach 3 CNC cutting 1/32" too far in both X and Y axis
« Reply #1 on: November 10, 2014, 07:05:13 PM »
Is home also offset 1/32"
 or is it now travelling further for the same dro indication. e.g you command x 3.0 and it travels to X=3.03125
Did you use exactly the same .xml file from your old computer.?

If everything is offset, I would look at your homing speeds and your debounce settings on the limit switches and see if they have changed.
If it is traveling further, look at your motor tuning, pulse frequency if using the PP. Have you run the PP driver test?
Are you losing steps on rapids to X-- and Y--?

Graham
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Graham
Re: Mach 3 CNC cutting 1/32" too far in both X and Y axis
« Reply #2 on: November 10, 2014, 09:29:00 PM »
If I command it to move, say 3.0", it will move that amount and the DRO's read 3.0". Not 3.03125"
The XML is the one from my old computer.

What does debounce settings do?

I have run the PP test and the computer has a great signal. Very straight with very little to no interruption.

How would I check to see if my X and Y are losing steps at rapids to --?
Re: Mach 3 CNC cutting 1/32" too far in both X and Y axis
« Reply #3 on: November 10, 2014, 10:01:53 PM »
The debounce settings add some delay in seeing limit switches. If they are significantly different, it could move he home position as the time that Mach sees the switch is changed

Easy way to look for lost steps is to write a short GCode program to exercise the motors. You will need some way to determine the actual position of the spindle.
For example, put a piece of rod in the spindle and set up a dial indicator near X=3.0 Y 0.0. Move the spindle to X3 y0 and zero the indicator. Make sure that it is not bottomed. A 1" or 2" dial indicator would be safest.
Then execute
G0 X 0
G1 X 2.8 F10
G0 X 0
G1 X 2.8 F10
G0 X 0
G1 X 2.8 F10
G0 X 0
G1 X 2.8 F10
(Then check the position)
G1 X 3.0 F1

You should adjust the distances and speeds to match you mill. You could go to X 3.0 each time but it is probably a better test to go back and forth a number of times before you bother to check.
When you command X 3.0 the dial indicator should still be zeroed. If you are losing steps on the rapids back to X 0, the indicator will read high.

I suggested losing steps in the minus direction because you are gaining 1/32" when traversing in the plus direction. I is probably worth doing this test in all directions X+, X- Y+ Y-. The key is that your test program rapids in one direction and moves at cutting speed or less in the opposite direction.

Graham
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Graham