Constant Z (MILL)

This cycle machines multiple surfaces by feeding down in the Z-axis as specified in the Z Step parameter, removing all possible material at that Z level via the method specified by the Operation setting (Contouring, Pocketing, Zig-Zag), and then feeding down to the next Z level. This is repeated until either the Z Depth parameter or lowest surface point is reached.

In order to use Constant Z correctly, it is important to know how the system generates the tool path. It starts by calculating the cross-sections of all designated surfaces at each Z Step level. Each cross-section represents the pocket boundaries and islands at each Z level, which the system then sends to the Pocketing with Islands routine to calculate the tool path at each Z level. If a Path ID is specified, it becomes the outer pocket boundary, with any specified surfaces within the pocket treated as islands at each Z level. If Path ID is set to NONE, then the outermost boundaries of the surface(s) become the pocket boundary. Generally speaking, surfaces with concave edges will not need an outer pocket curve, while surfaces with convex edges will. (see graphics below)

Constant Z Machining without a Path ID

Constant Z Machining with a Path ID

Pocketing with Islands

The same rules that apply to Pocketing with Islands therefore apply here. However, it is the system, not the user, that is creating the pocket boundary and islands in this case. This makes complying with the rules more difficult as it requires some forethought by the user to see that the surface cross-sections do not field invalid pocket and island curves.

In general, a valid pocket with islands consists of an outer closed curve which surrounds smaller closed curves, none of which may intersect each other or the outer curve. If you can imagine slicing horizontally through the surfaces at the various levels you wish to machine, you must ensure that the resulting cross-section at each level should field valid non-intersecting curves. If it does not, the system will either generate an incorrect tool path or give an error message.

If the system detects a cross-section area where the boundary curve is not closed, it will close it automatically. This feature allows the machining of open ended surfaces such as a half pipe. In certain cases this may not yield the desired result and you will need to edit the surface to be sure it fields the desired closed boundary curve.

The Constant Z cycle supports the use of upper and lower check planes. Any cuts that would otherwise occur above or below the specified Upper or Lower Check Plane will be excluded. This feature is useful for containing your machining strategy to a specific part region.

Rules for Using Constant Z Level Machining

Multiple surfaces may be designated.
If a Path ID is specified, it becomes the outer pocket boundary. This boundary must enclose, but not contact, all designated surfaces.
Check Curves are not permitted.
A surface which generates nested islands is permitted.
Z Step parameter can be entered as a positive or negative value. If entered as positive the cuts will be ordered from top to bottom, and if entered as negative from bottom to top. Bottom to top order is useful when machining protruding core type parts, allowing the tool to begin at the outermost profile gradually working inward and upward, thereby minimizing Z plunges into material.

Click here for graphic Example

Z-Step = (+)

Z-Step = (-)

To Use Constant Z Level Machining:

Select the surfaces to be machined in the 3D Cycle Data Tab.
Set the Path ID to the desired curve ID if using a boundary, or set to NONE if no boundary is used.
Set the Step Over parameter in the Cycle Data Tab.
Set the Z Step parameter in the Tool Info Tab.
Set the maximum depth in Z Depth (optional - can be left at 0).
Set the 'Stock Allow' in the Cycle Data tab and 'Fin Allow' in the 3D Cycle Data tab in order to provide allowance at the walls and planar bottom surfaces respectively.


Z-Step = (+)	Z-Step = (-)