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  1. #16
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    Nov 2017
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    FWIW one of the youtube creators recently covered a similar thing. I think in his case it may have been a CNC plasma, but his comment was along the lines of "although I originally thought my brain could cope - it couldn't, and having the orientation on the display being backwards to the physical travel has caused me a few crashes".
    So definitely stick with having your jog directions intuitive!

    In his case it was a simple stepper direction change - but sounds like for you its a case of finding the layer/setting that doesn't match the rest of the system.

    Although I can never remember which is which, probably the best thing would be to set everything so it conforms to the standard +ve and -ve directions for the axes. If for no other reason than it being "standard", so should mean that if you ever need to collaborate with an industry based CNC person or have someone looking over your shoulder - it won't fry their brain with the axes being backwards. Likewise if you're looking at someone else's gcode.

    Steve

  2. #17
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    Sep 2009
    Location
    Newcastle
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    There are well established conventions for axis direction etc.

    You need to think of the TOOL moving, not the table.

    As you stand in front of the machine:
    Tool moving from left to right is X+
    Tool moving from close to you, to far away is Y+
    Tool moving up towards the sky is Z+ (moving down towards ground is Z-)

    This is to have coherent set of directions from start (design) to finished part.

    Sure you can reverse things. On a square block that's not too hard.
    But what about a workpiece with existing features / funny shape? Reversing is inviting screw-ups.

    Strongly recommend you set it up in the usual convention and train your brain.

    Look at the tool in relation to the stock. Don't focus on the table.

  3. #18
    Join Date
    Dec 2007
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    Adelaide
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    402

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    Quote Originally Posted by pippin88 View Post
    There are well established conventions for axis direction etc.

    You need to think of the TOOL moving, not the table.

    As you stand in front of the machine:
    Tool moving from left to right is X+
    Tool moving from close to you, to far away is Y+
    Tool moving up towards the sky is Z+ (moving down towards ground is Z-)
    The way the dro and internal co-ordinates operate is fixed and looks like it can't be changed - right jog is positive - left jog is negative so I guess the controller follows established convention, I'm new to cnc and maybe this is how all motion controllers are setup.This is fine if the motion controller has been setup for a timber cnc router with the Z axis on an overhead gantry - a cnc machine with a fixed Z axis and a moving XY table is a little bit different in that moving the table towards the right brings the Z axis closer to the left side of the table so the dro (and internal co-ordinate system) should be counting backwards towards zero, I've done a little sketch to illustrate the difference - the X and Y axis have effectively been reversed.


    This did create an issue for the person new to cnc (ME) - with my engraving test work piece clamped to the table I located my datum point at the lower left corner - this is the point I picked when working out the tool path in Fusion360 - I zeroed all 3 axis to that point - press start and wait - the engraving did take place but not where I expected - it was upside down and moved to the right. My workaround was to rotate the workpiece 180 deg then clamp it down - the same datum point is used as the zero reference - in this instance it would now be at the top right, this does work I tried it, I can't see that an odd shaped workpiece would cause problems. There is another way though, I found Fusion 360 has an option to flip the X and Y axis at the time you are working out a tool path so no need to flip the part on the mill table and I guess this is what I'll be doing - being totally new to cnc I don't know but maybe this is just standard procedure.

    m350 question.jpg

  4. #19
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    Sep 2009
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    Newcastle
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    I don't quite follow you about what happened with the engraving.

    You need to think about the tool moving in relation to the workpiece.

    Forget about the table moving.

    Look at the tool and the stock.

    X+ moves the tool rightwards in relation to the stock
    (This means table moves left on a mill).

    You may have axes reversed.

    X+ jog should move the tool rightwards in relation to the stock (table moves left)

    Can you show a video?

  5. #20
    Join Date
    Dec 2007
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    Adelaide
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    Quote Originally Posted by pippin88 View Post
    I don't quite follow you about what happened with the engraving.

    You need to think about the tool moving in relation to the workpiece.

    Forget about the table moving.

    Look at the tool and the stock.

    X+ moves the tool rightwards in relation to the stock
    (This means table moves left on a mill).

    You may have axes reversed.

    X+ jog should move the tool rightwards in relation to the stock (table moves left)

    Can you show a video?
    Yes you are correct - if I forget about the table moving and just look at the tool and the stock then X+ should move the tool closer to the stock and X- moves the tool back away from the stock, there are parameters in the motion controller for this, - I'll get a video or two uploaded once the Xmas family duties are all done with in a few days.

  6. #21
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    Dec 2007
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    Adelaide
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    Relatives have departed and I now have some time to my self - I drew up a simple engraving test in Fusion and made a video - link is here

    https://1drv.ms/v/s!AhR6y7vV52cIjBs5A-lH2t1F8jsV


    In Fusion I set the bottom left corner as the 0,0 point and made a mark on the paper and set this as the 0,0 point of the work co-ordinate system, I expected (possibly incorrectly) the 'engraving' to take place in what would be the first quadrant of the cartesian co-ordinate system ie the right and above the 0,0 point - as the video shows it was down and to the right.


    Just prior to making this post I downloaded a pdf copy of 'CNC Machining for Engineers and Makers' by NexGenCam it looks informative - now that I have a bit of time to myself I'll do some reading.

    Screenshot 2022-01-08 155948.jpg

  7. #22
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    Sep 2009
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    Newcastle
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    You have both X and Y inverted.
    A common mistake when setting up a moving table machine.
    Depending on software may be an easy fix in software.

    Or you can do it by changing the wiring. Swap the polarity of one pair on each stepper (assuming 4 wire motor).

  8. #23
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    Adelaide
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    Yes my axis were reversed - easy enough to change either in the motion controller parameters or at the stepper driver dip switches, I made the change and did another test run with the 0,0 point in Fusion360 set to the bottom left corner and used the same corner for the test run (felt tip pen again) - this time the engraving - letter G - it was positioned where I expected, the jog buttons however now operate the opposite way.


    I have for now stuck some masking tape labels over the jog buttons, I'm a bit concerned that I'll jog the table in the wrong direction and wipe out a cutter or something even more serious. I'm not sure if this is the right thing to do as it doesn't reinforce the concept that I should be thinking in terms of the cutter moving rather than the table moving.


    This is my first foray into CNC - I guess the feeling will eventually go away but it is a bit un-nerving to watch the machine take off on it's own, with me thinking have I done it right ? - is the cutter going to slice through my vice ?

    20220109_115347.jpg 20220109_115353.jpg

  9. #24
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    Sep 2009
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    Newcastle
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    Can you make a video of the jogging including which button you are pressing etc

  10. #25
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    Dec 2007
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    Adelaide
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    Quote Originally Posted by pippin88 View Post
    Can you make a video of the jogging including which button you are pressing etc

    Link to jog buttons video


    https://1drv.ms/v/s!AhR6y7vV52cIjCH1kbiR6IJ1ZhCd

  11. #26
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    Dec 2007
    Location
    Adelaide
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    A small update I drew up a 12mm sq x 5mm high block to be machined on the end of a bit a scrap Al I've been using for testing, the machining went well and end result looked ok but not great, but it came out a bit undersized 11.935mm x 11.933mm and a few hundreths of a mm tapered, I watched a few youtube videos on backlash and after some checking ruled that out, I checked the cutter for runout (ER collet chuck) and found just over 0.07mm, way more than I expected, no amount of cleaning, checking for burrs, remounting etc made any difference, I pulled the chuck and checked with a bench magnifier I could see a wear mark on the nut at the point marked W on the sketch - this is the eccentric bit that pulls the collet from the chuck, and the point at W is not supposed to touch the collet at all - being eccentric it was probably pushing the collet one side only - a minute or two on the lathe to skim a few thou off and the cutter runout came down to just under 0.015mm - not perfect but a huge improvement.

    Screenshot 2022-01-12 233936.jpg Screenshot 2022-01-12 234111.jpg

  12. #27
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    Sep 2012
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    York, North Yorkshire UK
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    Quote Originally Posted by familyguy View Post
    A small update I drew up a 12mm sq x 5mm high block to be machined on the end of a bit a scrap Al I've been using for testing, the machining went well and end result looked ok but not great, but it came out a bit undersized 11.935mm x 11.933mm and a few hundreths of a mm tapered, I watched a few youtube videos on backlash and after some checking ruled that out, I checked the cutter for runout (ER collet chuck) and found just over 0.07mm, way more than I expected, no amount of cleaning, checking for burrs, remounting etc made any difference, I pulled the chuck and checked with a bench magnifier I could see a wear mark on the nut at the point marked W on the sketch - this is the eccentric bit that pulls the collet from the chuck, and the point at W is not supposed to touch the collet at all - being eccentric it was probably pushing the collet one side only - a minute or two on the lathe to skim a few thou off and the cutter runout came down to just under 0.015mm - not perfect but a huge improvement.

    Screenshot 2022-01-12 233936.jpg Screenshot 2022-01-12 234111.jpg
    Hi Familyguy,

    I have a couple of ER collets that seem a little tight in the nut, I'd assumed that the groove in the collet was slightly narrow.

    Your picture explains a lot, thanks.
    Best Regards:
    Baron J.

  13. #28
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    Sep 2009
    Location
    Newcastle
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    Quote Originally Posted by familyguy View Post
    Jogging is as expected.

    X+ moves tool right.
    Y+ moves too away.

    You just gotta train your brain. Look at the tool. Don't look at the table.

  14. #29
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    Aug 2019
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    Revesby - Sydney Australia
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    54
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    554

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    Install 2 MPGs?

    One above the spindle, which jogs the cutter relative to the job.

    One below the spindle, which moves the table.

  15. #30
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    Dec 2007
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    Adelaide
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    I now realise that thinking in terms of the tool moving is something I should get used to - I guess that I should be thankful for small mercies, actually getting the mill to machine or engrave has been quite painless, getting it to do so in the right place was a bit of a head scratch, I was hoping to find some sort of tutorial on youtube that explains the process from start to finish on setting up the axis, the home position etc. but found nothing that would really assist me. The publication I mentioned in post #21, I found for me was actually very good as it assumes no prior knowledge, explains the process and gives reasons why things are done a certain way, it has the look of a text book used for a tafe or trade course.


    Getting used to the tool moving rather than the table moving reminds me of my car - the drivers seat is the memory type that is power operated with servo motors, to make it easier to get out of the car it retracts to the rear when the door is opened, even though I know this, I still at times get the feeling that the car is rolling back as I open the door when it is actually only the seat moving.

    Quote Originally Posted by nigelpearson View Post
    Install 2 MPGs?

    One above the spindle, which jogs the cutter relative to the job.

    One below the spindle, which moves the table.
    I'm not sure at this stage how to rig up 2 MPG's - the jog buttons on the motion controller are not really like a MPG - they can be

    (1) programmed (on the control panel ) to move a specific distance - either 1 of 3 presets or a custom distance entered by the operator, or

    (2) operate in continous mode in one of 2 speeds - low or fast. The MPG controller has pulses generated by the handwheel with a choice of 3 user selectable speeds, and I don't think it was intended to replace jog buttons - I find it useful for touching off on the stock to set the 0,0 datum point, the finest setting moves around .001mm per pulse (I div on the handwheel).

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