Machine Tool Coordinate Systems and Conventions

[tblough]

Just though I'd post this here as a reference for the DIY'ers when setting up their machine tool coordinate systems. All illustrations were taken from ISO 841:2001(E) Industrial automation systems and integration — Numerical control of machines — Coordinate system and motion nomenclature

Z-Axis
The Z axis is parallel to the principal spindle of the machine.

• On machines used for milling, grinding, boring, drilling and tapping, the spindle rotates the tool.
• On machines such as lathes, cylindrical grinders and others which generate a surface of revolution, the spindle
  rotates the work piece.
• For cutting and forming machines, the Z axis shall be perpendicular to the work-holding surface.
• For coordinate measuring machines, the Z axis should be collinear with the acceleration of gravity vector (i.e.
  perpendicular to the surface of the earth).

X axis
Where possible, the X axis shall be horizontal.

• Machines with rotating tools
  • Horizontal Z axis: Positive X shall be to the right when viewed in the negative Z direction.
  • Vertical Z axis, single column: Positive X shall be to the right when viewed from the front of the machine into the
    column.
  • Vertical Z axis, gantry type: Positive X shall be to the right when viewed from the principal spindle to the left-hand
    gantry support.
• Machines with rotating workpieces
  • The X axis shall be radial and parallel to the cross slide. The positive direction shall be away from the axis of
    rotation.
• Machines with no spindle
  • For cutting machines, positive X shall be parallel to and in the principal direction of cutting.
  • For coordinate measuring machines, positive X shall be defined by the manufacturer.

Y Axis
Positive Y shall be in the direction to make a right-hand set of coordinates

Examples

[cncsnw]

Excellent material.

Just to make it abundantly clear: the right-hand coordinate system, and the X, Y and Z directions shown in the examples, refer to cutter movement through the workpiece.

In situations where the workpiece moves, rather than the cutter (as in the X and Y directions on a typical vertical mill), the table movement is opposite the desired cutter direction. This is clearly indicated in the examples above via the ' (prime) suffix: the X' direction is table movement, opposite the conventional X direction. The Y' direction is table movement, opposite the conventional Y direction.

[slodat]

Some additional explanation that was offered up in my mill build thread that I thought would be helpful for others..

What does forward/back on the Y mean? More specifically, where does Centroid want the table to be in the homed position? I'm assuming X0 is table all the way to the right. Still unclear where the saddle is.. at the operator or at the column?

Table closest to you is Y+
Furthers away (toward the column) is Y-

Centroid doesn't care where you home. It becomes the control Datum point.

Don't worry, you are learning.....ask all the questions you need to. You do need to square away your understanding of spindle movement.

First decide on what axis is what. The Z axis is your spindle and Z up, away from the work is Z+. You then decide which axis you want to call X. X+ and X-, and Y+ and Y- directions are then determined by the right hand rule.

With the axis names and directions determined. You home the table where ever YOU want to home the table. Once you decide on where you want the home position, you place the home switches so that they close in that spot. You can then add limit switches at the extents of your travel on each axis if you desire. Whether you use limit switches or not, you then need to set soft limits.

On the VCP, X+ is X+, Y+ is Y+ and so on. If the location of the X or Y arrows on the VCP does not coincide with YOUR axis designations, you can reverse the labels in setup.

You can home the table anywhere you want.

If you don't know what you want, then home it X- (table right / tool left) and Y+ (saddle forward / tool away).

The jog buttons arrows and directions represent tool movement across the part.

To make the tool move across the part in the X+ direction (left to right), the mill table has to move from right to left. You press the right-pointing (X+) jog button to make that happen.

To make the tool move across the part in the Y+ direction (from front to back), the saddle has to move toward you. You press the up-pointing (Y+) jog button to make that happen.

The minus limit switch is the switch that would be tripped if the tool moved too far in the minus direction (X-, Y-, or Z-). The plus limit switch is the switch that would be tripped if the tool moved too far in the plus direction (X+, Y+ or Z+).

[sbtennessee]

I am installing an OAK control to replace an old PC control in a single punch machine with an X and Y axis attached to a flat table that positions a piece of sheet metal under the ram to be punched. The machine is equipped with a homing proximity switch on both the X and Y axis and when the machine started up with the old control, the operator pressed the HOME switch and both the axis moved in the plus direction away from the punch at a slow speed until the proximity switch was trigged at which point the axis would slowly move in the negative until the switch went off again, this could be a long move, up to 40” depending on where the axis was at start up. After the homing sequence, the X and Y axis would display a position in relation to the distance to the center of the punch (datum).
Is it possible to have a similar operation with the OAK control? Thanks in advance for your advice.

[tblough]

When CNC12 is configured to home to switches, that is the standard operation.

[suntravel]

Figure A.3

U and W axis labels will not work on a lathe, because U is for incremental moves X axis, W for incremental moves Z axis.

Uwe