why is machining referred as 2.5 axis?

[60rock]

Why is machining on a 3 axis machine called 2.5 axis?

Thanks,

[Caprirs]

The 2.5D or 2-1/2 axis refers to the common parts where the Z axis plunges into the workpiece and then does not move while the X & Y axes do all the work. By comparision, 3D typically refers to surfacing/mold/die type operations where all three axes move simultaneously.

Most VMCs will move all three axes simultaneously, but the CAD/CAM packages that generate the code differentiate between the types of operation.

[nwrepair1]

Most machine controls do not have 3D capability. The X and Y axis interpolate together and the Z axis moves second. In a true 3D control, X Y and Z are fully interpolated. If you look at the readout in a 3D control, the three numbers are moving simultaneously.

[DareBee]

yep - full 3 axis takes massive amounts of calculations and 2.5d is really quite simple.

[Andre' B]

Most machine controls do not have 3D capability. The X and Y axis interpolate together and the Z axis moves second. In a true 3D control, X Y and Z are fully interpolated. If you look at the readout in a 3D control, the three numbers are moving simultaneously.

I would argue with that. Every mill I have run could do 3 axis moves, just that some were limited in how fast they could do it compared what is expected in a modern machine.

I have seen a few CNC knee mills that would not do simultaneous 3 axis but I never run one.

[HIRAH]

my understanding of 2.5 axis machining is that you can only create an arc in 2 planes simultaneously. all the cnc machines i have used can cut x,y and z at the same time. but not arcs on 2 planes at the same time. plus even with a 4th axis, they only move 3 axis at one time.