3d vs 2.5d, is it well defined?

[fishtoprecords]

I am not sure that I understand the difference between 2.5D milling and and 3D. Is there a clear difference, or is the difference as fuzzy as my understanding?

[Gadgetman!]

The big difference is that on 'real 3D' you can undercut features or make holes that are not vertical.

[PsyKo]

Basically, you can do 2.5D with a 3 axis machine, and 3D with a 4 axis (or more) machine.
As mentioned by GadgetMan! 3D allows undercut.

But you can achieve 3D milling with a 3 axis machine by turning the piece being milled (with fixtures for instance). But it requires more work and precision.

[twforeman]

The way I define it when I am talking about CAM software (and have always heard it defined) is that 2-1/2D means making flat bottomed pockets and profiles.

3D means full surface profiling. Not undercuts.

Doing undercuts requires a 4 (or more) Axis machine, but is still called 3D.

[janapriya]

I am not sure that I understand the difference between 2.5D milling and and 3D. Is there a clear difference, or is the difference as fuzzy as my understanding?

In general 2.5D is a sub domain of 3D. Roughly, 2.5D we have the complete control over X, Y and but half control over Z axis. In milling it is physically impossible to reach certain regions (undercuts), along Z axis, given we have material left towards the bit.

[cvoinescu]

I'm with twforeman on this one. 2.5D is to 3D like a poster print is to a full color print. With 2.5D, you can have features at various depths, but all have flat tops and bottoms. With 3D, you can have arbitrary shapes (although only a subset can be milled on a 3-axis machine). A 2.5D object can be described by a small number of 2D drawings, each corresponding to a set Z depth. A 3D object requires a true 3D file format.

[Threefer]

I always thought it was as twforeman and cvoinescu describe it. You can also do shallow undercuts on a 3 axis machine using a ball end cutter with a smaller shank than the ball.


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[edwardrford]

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-Edward

[janapriya]

Good one!

[Threefer]

Awesome.

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