Centroid Community CNC Support Forum

Dear all,

I am a newbie in CNC field. Start learning the related hardware and software knowledge few weeks ago.
As far as I know, the 4th axis in CNC program are all internally defined as rotation degree.
But I want to build my CNC a second independent Z-axis and program it move up and down in metric distance, just like x, y and original z axis.
Is it possible to do this by using Acorn CNC controller or software interface?

A fourth axis can be defined as either linear or rotary with Centroid products. It can be assigned any available label but it can not be assigned a label that's already being used. It can be used just like any other axis but it's not "independant" ie.. you can't program an XY move and while that move is progress, tell the 4th axis to be doing something else. You can however program an move with all 4 axes and it will interpolate all axes to move "in sync" so that they all end up at their commanded positions at the end of the move.

diycncscott wrote: ↑Mon Sep 25, 2017 5:16 pm you can't program an XY move and while that move is progress, tell the 4th axis to be doing something else. You can however program an move with all 4 axes and it will interpolate all axes to move "in sync" so that they all end up at their commanded positions at the end of the move.

Thank you so much for the reply. This clarified a lot. Ok, I will use A as my label for second Z-axis. This second Z-axis is fixed at where the Spindle should located. By the way, I don't use this design for real CNC machining. Actually, it was used as some robotic system. My purpose is: using G-code to move the x, y, z axis to a desired position, stop them and move A axis up and down. So, in this case, there should be no problem, am I right?

Regarding the "sync", does it mean, to include the 4th axis in x, y movement, I need to write G-code that includes all 4 axis. Such as, G00 X0. Y-10. Z0. A-15.

You can use any legal axis label that is not already in use.

Legal axis labels are A, B, C, U, V, W, X, Y and Z.

For what it's worth, 'W' would be the "standard" label for a linear axis which moves parallel with Z. 'A' is typically used for a rotary axis with its axis of rotation parallel with X movement.

You do not have to include X, Y and/or Z on a line which moves your fourth axis.

You can command a fourth-axis-only move, and only the fourth axis will move.

Scott's point was that if you do want the fourth axis to move simultaneously with one or more of the other axes, then you have to command all of them with the same line of G code, and they will all then be coordinated to reach the endpoint of the move at the same time.

Sometimes when a person asks whether an axis can be made to move "independently", they mean, for example, "can I have my 3-axis machine running a program in X, Y and Z, while I use jogging controls or PLC logic to make the 4th axis do something that is not part of that CNC program at all?". The answer to that is No.

I see. Thank you so much. I remember in a G-code introduction video used "W", now I have a better understanding. Such a great relief. Acknowledged the problem in language I used to describe my problem, totaly make sense.