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Thread: I need help! Negative X, Y Coordinates from Home

  1. #1
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    I need help! Negative X, Y Coordinates from Home

    Will try to make this as short as possible

    I have a Shapeoko XXL and added a new, more robust Z axis. Not being able to use Carbide Motion anymore, I am now using Universal G Code Sender. Everything has gone very smooth with the addition of the new axis, but I have one strange thing going on.

    When I home, it goes to the back right corner like always, but now X+ and Y+ go to the right and back. Meaning if I want to move to the front left to set zero's there and start the job I am in negative coordinate numbers. All of the Gcode in jobs that I have created are in positive numbers. So, when I start a job it immediately errors out and tells me I am out of my limits. I have gone through the settings for GRBL, but I'm still having trouble finding the correct settings to correct this.

    I have added the settings for my machine here. I tried changing $3=3, but that just made it try to home to the back left.
    Hopefully someone here knows what I'm talking about and can help.

    Thanks!!
    $0=10

    $1=255
    $2=0
    $3=2
    $4=0
    $5=0
    $6=0
    $10=255
    $11=0.020
    $12=0.010
    $13=0
    $20=1
    $21=1
    $22=1
    $23=0
    $24=100.000
    $25=2000.000
    $26=25
    $27=5.000
    $30=1000
    $31=0
    $32=0
    $100=40.000
    $101=40.000
    $102=320.000
    $110=5000.000
    $111=5000.000
    $112=1000.000
    $120=320.000
    $121=400.000
    $122=200.000
    $130=889.000
    $131=437.000
    $132=150.000

  2. #2
    You seem to have changed the invert bit, $3 which has reversed at least one axis.

    You can mechanically reverse the Z by installing the Z-axis spindle carriage plate upside down --- static pulley should be on the left

    You can electronically reverse the Y by powering down and swapping the motor controller connectors for Y1 and Y2

    Naturally any stepper motor can be reversed by re-wiring it.

    and you could reverse any axis by adding / subtracting the appropriate bit from $3, so to invert X and Y both you'd set $3 = 1

    But I think you have travel right (which is weird, since $3 is normally 6) and it's correct for

    > X for the axis along the gantry (left and right, with right being positive)
    > Y for across the gantry (toward and away from you, with away being positive)

    So what you need to do is move to the appropriate point and then zero out to set that as home, then the coordinates will be as you expect them.

  3. #3
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    Brings back memories of when I was trying to get my GRBL blue light laser running. I finally gave up and sold at a great loss to get rid of it. My suggestion is put another controller on it, even a Mach3 with Ethernet interface. Not sure if you have real stepper motor driver boards or ones that are incorporated into a all in one motherboard like mine were.
    Retired Guy- Central Iowa. , Ray Fine 20w Galvo Fiber laser (SOLD) , LightObject 40w CO2 Laser and Chiller, MakerGear M2 3D Printer. Qe60+ Vinyl cutter. Fine Line Automation 4x4 CNC Router

  4. #4
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    Thanks for the replies. The Z axis is fine, I think. The normal home for the Z is at the top and from looking at the G code in some of my projects the Z is always a negative number.

    It's the X and Y that seem to be wrong. I don't need to reverse the travel of X and Y, but I need to reverse the coordinates.

    Now, when the X and Y go away from home( to the left and to the front) they go into negative coordinate numbers and they should be in positive numbers. I don't understand why this happened? or how to fix it?
    Last edited by David Justice; 09-12-2018 at 6:26 PM.

  5. #5
    I'm afraid I'm not understanding your difficulty --- if you could describe your difficulty in more detail --- usually helps to note:

    - what you did
    - what you expected
    - what actually happened

    I sent you a PM with some links

  6. #6
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    Quote Originally Posted by David Justice View Post
    Thanks for the replies. The Z axis is fine, I think. The normal home for the Z is at the top and from looking at the G code in some of my projects the Z is always a negative number.

    It's the X and Y that seem to be wrong. I don't need to reverse the travel of X and Y, but I need to reverse the coordinates.

    Now, when the X and Y go away from home( to the left and to the front) they go into negative coordinate numbers and they should be in positive numbers. I don't understand why this happened? or how to fix it?
    Are you sure the normal Home is not lower left? GRBL is actually a pretty decent control system.
    Last edited by Bill George; 09-12-2018 at 10:18 PM.
    Retired Guy- Central Iowa. , Ray Fine 20w Galvo Fiber laser (SOLD) , LightObject 40w CO2 Laser and Chiller, MakerGear M2 3D Printer. Qe60+ Vinyl cutter. Fine Line Automation 4x4 CNC Router

  7. #7
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    I don't understand my difficulty either! I guess I'm not articulating it very well. I'll try one more time.

    When using Carbide Motion and I jog away from home to the front left to start a job I am in positive coordinates. I start the job and it runs fine.

    When using UGCS and I jog away from home to the front left to start a job I am in negative coordinates. I start the job and immidiatly get an error that I have reached soft limits.

    That's my difficulty, I hope this explanation works. So, why not just use Carbide Motion? I want to take advantage of the added Z axis travel.

    Bill-The limit switches are designed to go on a certain spot on the machine, so home has to be where it is.

  8. #8
    I believe the thing which you're not understanding is that there are several different sets of coordinates. Carbide Motion 4 mostly hides this from you, but in Universal G-Code Sender you have to understand them.

    - machine coordinates --- this is what the machine is at after it homes and is hidden from the user in CM4
    - G54 --- this is the default work coordinate system and what one sets when one sets zero in Carbide Motion 4 --- http://www.shapeoko.com/wiki/index.p...ance_of_travel
    - other work coordinate systems --- G55--59 --- UGS will allow you access to these --- see: http://www.shapeoko.com/wiki/index.p...dinate_Systems

    You need to find a good tutorial on setting zero in UGS, if you're not using a recent/nightly build, I'd recommend updating (the problem may be that you're using a version which supports Grbl 0.9, not 1.1) --- used to be that UGS was the recommended software, maybe the old instructions will help: shapeoko.github.io/Docs/software.html (but they're pretty basic) and if you haven't yet, review: docs.carbide3d.com/tutorials/tutorial-homing/

  9. #9
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    David, a quick thought. When I set up a job in VCarve Pro the material size dictates for me anyway where I really want my 0,0 after my machine zeros at front left I just jog over the material wherever its located and zero my x,y and z, actually I zero my z on the workpiece surface.
    Retired Guy- Central Iowa. , Ray Fine 20w Galvo Fiber laser (SOLD) , LightObject 40w CO2 Laser and Chiller, MakerGear M2 3D Printer. Qe60+ Vinyl cutter. Fine Line Automation 4x4 CNC Router

  10. #10
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    From what I just read that Mr. Adams typed, it comes down to Carbide Motion "automajically" sets up certain conditions for the end-user that makes things easy. When you move to the more "capable" software, the end-user is responsible for certain setups before running the job. The latter is what I have to do with my Camaster...I have to tell the machine where x0,y0 is for a particular job ... and remember to do that for each and every job. There are no assumptions made by the WinCNC control software, just as it appears that your Universal G-Code application is expecting. Not doing that at minimum results in a limits error which is merely frustrating, but it can also lead to damage to a cutter, the material or something else. There should be a defined process in your Universal G-Code software to set the "x0,y0" for a given job before you run the code...I would think that would be something akin to moving the point of the cutter to the spot you want to be "x0,y0" based on how you drew out your design and created your tool paths and then clicking on a button or entering a command. Think of it as a "temporary" zero point that you must set each and every time you want to run a job. And yes, it's essential you know where "zero" was placed in your drawing/tool path for that job. Sometimes we do that at the center of the material and sometimes we do that at front, left, etc. "Where" matters.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  11. #11
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    Well gentlemen, with your help I think I have finally figured it out. Will, your link about work coordinates was great. I also found a book called CNC fundamentals and read through the chapter on work coordinates. I was definitely looking at the machine and work coordinates wrong. It was made worse by a second error that I wasn't even seeing. For some reason the post that I was using was putting in code for a tool change at the beginning of the code and UGS didn't lie it.

    I fixed my soft limits and found another post processor that works and now I have run 2 successful jobs.

    Thank you all very much for your help!! I would never had figured it out myself.

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