# Thread: What is the difference?

1. ## What is the difference?

What is the difference between 2 1/2 D and 3D as it applies to a cnc machine. Can anyone give me an example of both?

Thank you.

2. 2.5d is like xy milling with depth. 3d milling is 3 axis at the same time.

a 3d surface would be 3d milling, cutting a circle or pockets would be 2.5d

Jon

3. The difference is .5D

Sorry! I just had to do that

Put it this way: if you had a cnc mill with only X and Y moving the table, it would be a 2d cnc machine. You could still drill holes with a manually operated quill, or plunge the tool into the work manually and then press cycle start to run a simple X and Y positioning or machining program.

If you then power the Z axis with a servo, this can take care of the same movements that you were creating with your arms. This would be like 2.5D: X and Y can move singly or simultaneously, but X, Y and Z do not move simultaneously.

In the old days of cnc, you might have saved a few bucks on your cnc controller if you did not require 3 axis simultaneous motion. But with modern cnc's, even hobbiests can enjoy that luxery.

Full 3d requires that all 3 linear axis can move simultaneously. This is typically called for in complex surface mold machining. So those of us who use a 3 axis cnc, but mostly do hole drilling, or simple contour cutting, call what we do "2.5D" machining, because we are not really using 3 axis simultaneous contouring, yet, the Z axis is still fully controlled by the cnc.

4. Just out of curiosity, Would photo carvings be 2.5 or 3D? Thanks- Robbie

• 3D, but with photo carvings the Z axis usually doesn't move more than about 1/16". With 2 1/2D, once the tool ramps or plunges to the cutting depth, the Z doesn't change during the cut, until the tool is retracted. With 3D, the Z is constantly changing (usually) during the cut.

• If you twist your thinking sideways a lot of cam generated code for complex mold surfaces is 2.5D; X remains fixed while Y and Z move, or Y is fixed and X and Z move.