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Can't always zero the X, Y and Z axis in Mach.
« on: June 16, 2009, 12:25:35 PM »
When I load a gcode from sheetcam to cut out a part sometimes I can get Mach to zero and sometimes I can't. I've cut a male part and had it work but when I loaded a part to do a relief cut it didn't let me zero the x, y and z axis. I'd press the zero button next to the axis and nothing would happen. I can't understand why. There must be some button I haven't activated.
Thanks,
Lindsay

Offline Hood

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Re: Can't always zero the X, Y and Z axis in Mach.
« Reply #1 on: June 16, 2009, 01:25:27 PM »
Could it be you are viewing the machine coordinates? You can only zero them by homing.
Hood
Re: Can't always zero the X, Y and Z axis in Mach.
« Reply #2 on: June 16, 2009, 03:09:21 PM »
That may have been it. I'm a little confused about the difference, machine coordinates as opposed to what? I did finally muddle through and get it to work, not sure exactly what I did.
Thanks,
Lindsay

Offline Hood

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Re: Can't always zero the X, Y and Z axis in Mach.
« Reply #3 on: June 16, 2009, 03:11:35 PM »
Machine coordinates are what Mach keeps a track of, Offsets are when you zero a DRO or type a number into the droetc.
Hood
Re: Can't always zero the X, Y and Z axis in Mach.
« Reply #4 on: June 17, 2009, 11:36:44 AM »
I guess that's the crux of my problem, I can't see how Mach could keep track of the machine coordinates. We have no encoders, only steppers. It's a router table, and all we are doing is sending a string of pulses to the steppers. Mach of course knows how many pulses we've sent and from there could derive a position. I am trying to run a test cut in the air above the substrate. I send the router head to a position 3" above the piece to be cut. Then I type in a value of 0.5" for the Z axis thinking this will redifine the Z axis as being 0.5" above the substrate. I then start the cycle but Mach ignores my redefinition and goes down too far to do my test cut in the air. Is there a way to do this?
Thanks,
Lindsay

Offline Hood

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Re: Can't always zero the X, Y and Z axis in Mach.
« Reply #5 on: June 17, 2009, 01:42:35 PM »
When you home the machine that sets the machine coords to zero. Mach can then calculate the amount of pulses it sends out and will keep a track on that so it knows where the axis is meant to be at all times. If you have steppers then it is open loop and is dependant on you not having lost any steps, with a servo system the loop is closed to the drives. Again Mach is only assuming the axis is where it is meant to be but as the servo drives would have faulted if it wasnt (within the following error) then that assumption is correct.

Now to your problem, if the DRO reads 0.5 after you have typed in and pressed enter then yes that should mean it is 0.5 above zero. Your code however could change that as it may be using a different offset, there are 254 offsets available to Mach. If you want to attach your code someone may find a problem there.
 Hood

Offline jimpinder

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Re: Can't always zero the X, Y and Z axis in Mach.
« Reply #6 on: June 17, 2009, 03:04:20 PM »
Lindsay - does your machine have "home" switches fitted, and do you "home" your machine at the beginning of each session.

Machine Co-ordinates are used by Mach to keep track of it's position, it includes in it any offsets for programs, tools, etc. It is for mach - and when you look at Machine Co-ordinates, it is difficult (sometimes) to equate them with the program we are running. The only way to alter these Machine Co-ordinates is to "Home" the machine by pressing "RefAllHome" this moves all axis, in turn, to their respective home switch, and then (if "auto zero" is set) it zeros the Machine Co-ordinates.

Machine Co-ordinates are viewed by pressing the "Machine Co-ords" buttong, the surround lights, or underlines, and you are now viewing Machine Co-ordinates.

If you do not have home switches fitted, then you can zero this in any position by pressing the RefAllHome button.

Mach will now keep it's position relative to its last zero mark, in Machine Co-ordinates.

This position will be no use to normal work on the machine, and therefore you should press the Machine Co-ords button. The surround will go out, and the DRO's will now show Program Co-ordinates. These are the ones you want to use when machining.

Jog you machine to the 0.0.0. position of the program and then press ZeroX, ZeroY and ZeroZ. This will zero the Program Co-ords display, and you are then in a position to start your program. An offset has been entered to tell Mach the difference between the two displays.

Provided your program has no G54 - G59P*** commands in it, which changes the "offsets" (i.e. the relationship between the Machine Co-ordinates and the Program Co-ordinates) then your program should run as you expected.







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