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Machine Axis & DRO Letter Designation

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  • Machine Axis & DRO Letter Designation

    I know you can designate any letter to any axis on any machine you want, it's totally personal preference, but what I'm wondering is there is a standard that most people go by???

    Reason being, my mill 3 axis readout box has X,Y and Z. I have it set up as X being the table, Y being the saddle and Z is the quill and knee. I think by standard I have the X and Y mixed up. I've often thought of switching them around but that is how they ended up when I first installed them as the box was marked input 1,2 and 3 and not in letters.

    The thought crossed my mind again the other day as I'm installing the readouts on my lathe, the control box for that machine is a 2 axis, they are designated X and Z. so if X is the cross slide as a standard then Z is the bed or longitudinal same as the table on the mill which is designated Y by standard.

    On the readout box for my T&C grinder which is also a 2 axis it has the letter designation of X and Y, so again X being the saddle or infeed and Y being the table. Since T&C grinders operations are basically lathe stuff why is there a difference in letter designation for the same axis on two different machines????


  • #2
    Yes, there are standards. Z axis is in line with the spindle, X and Y are transverse to the spindle axis. There are auxiliary U V W linear and A B C rotary axes and more. However, it can get a little slippery. A milling machine is pretty straightforward where you have a transverse movement identified as X, a smaller fore and aft movement as Y and the up and down knee movement as Z. Technically the quill should be an auxiliary axis but most people just lump everything that goes up and down as a Z.

    Now move over to a surface grinder. You've still got a left and right and an in and out and an up and down where the removal of material is customarily controlled by the up and down so it nominally looks like the mill axes. Technically though, the fore and aft (in and out) movement is Z since that's in line with the spindle axis but most people would still be most comfortable still thinking of table movement as being X and Y.

    On the lathe, the readouts usually adhere to convention and label movement of the saddle which is in line with the spindle axis as Z which is as it should be. Movement of the crosslide, transverse to the spindle axis becomes X. There isn't really a Y unless you had a third perpendicular movement like a milling accessory on the crosslide and the compound might be something like U' if you had a readout for it.

    There's no doubt several books somewhere explaining it all but as usual many folks just go with a guess or whatever pops into their head first - rather like statistics quoted by politicians.
    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill


    • #3
      I have a very hard time not thinking of the spindle axis of a lathe as the X axis, and the cross-slide axis as the Y axis. But I know a lot of guys don't do it that way.



      • #4
        The axis into the spindle on a lathe is the Z, cross slide X,
        The A,B & C rotate around the X,Y Z respectively.
        Google Cartesian coordinate system.


        • #5
          And for those of us raised up in the AutoCAD world, the natural axis would be X as left and right which would be the bed of the lathe as is is operated, the Y axis would be nearer and farther along the plane of the X axis as in the cross slide and Z would be the spindle of a mill attachment or up and down perpendicular to the X-Y axis.

          The reason for the exclusion of the Z axis in lieu of the Y axis would be that when using two axis in CAD that plane is defined by X and Y

          Not having more than a passing knowledge of cnc beyond the electronics side or G code at all, these are only my CAD biases put to paper... :>)

          Last edited by ironmonger; 05-02-2013, 09:49 AM. Reason: clarification (rectify axial brain fart)
          ARS W9PCS

          Esto Vigilans

          Remember, just because you can doesn't mean you should...
          but you may have to


          • #6
            TGTool, you pretty much summed it all up. I forgot to mention the surface grinder axis but you answerd it for me. The surface grinder is an exception to the X rule where it's designated as Z.
            I was aware that there were other letter designations for rotory tables and other accessories.

            TNX...... JL..........................


            • #7
              An example was to see was our 5 axis CNC 5" Horizontal Boring mill with a window of 96 " x 72 " by 60"
              The table ( L to R ) was X (96")
              The Headstock up/down was Y ( 60")
              The horizontal headstock Quill in/out was Z ( 28")
              The Table in/out was W (72") (note, same axis as quill !)
              The Table ( 60x 48) rotated and was B ( 360 degrees)
              The Auxiliary (18") Rotary Table was A (and was placed on the big table ) .
              So there was 6 axis possible, but we only could do 5 simultaneous at one time ( that's enough !)



              • #8
                Originally posted by metalmagpie View Post
                I have a very hard time not thinking of the spindle axis of a lathe as the X axis, and the cross-slide axis as the Y axis. But I know a lot of guys don't do it that way.

                You can think of the lathe as a vertical mill on its side (or as a horizontal mill).

                I'm more than annoyed by the lathe DRO at work which is a relic from ages ago, it shows the Z axis in wrong direction, makes inputting numbers a pain when you have to think of the sign.
                Amount of experience is in direct proportion to the value of broken equipment.


                • #9
                  Originally posted by JoeLee View Post
                  I know you can designate any letter to any axis on any machine you want, it's totally personal preference, but what I'm wondering is there is a standard that most people go by???

                  You may "call the axes anything you want", but to be accurate, take a look at the following pics.



                  • #10
                    I use my lathe X axis the other way around, so it takes of diameter as you wind it in. This way you can take a clean up pass, measure it and put that number into the DRO then it will count down the more passes you take. Once I get close I remeasure and go from there.

                    If it was like in the picture above it wouldn't work with the DRO as you would be going up in numbers not down.

                    The Z axis I use like in the picture because it takes off the closer you get to the chuck.



                    • #11
                      This is fun and I like the illustrations but I am not entirely convinced that it has always been as depicted. It is relatively modern history to me to hear Z connected with a lathe. I am not a programmer, but in the world I traveled in it was X and Y for the lathe. Could things have changed due to programming protocol changes? I don’t know, but as I said, fun!


                      • #12
                        Hi Mike,
                        I am not sure how new it all is, but the dedicated lathe DRO's come with X and Z on them. The 3 axis has Z0 and Z1 for the saddle and compound.



                        • #13
                          The axis designations for numerically controlled lathes date back a long way; almost to the beginnings in the early fifties. It was certainly in normal use when CNC started to become popular - perhaps late 70s?

                          It is true that machinists who worked only on manual lathes did not use the current axis designations in normal day to day work. I think referring to X and Z would have sounded a bit strange in that environment.