Plunge Roughing is machining away stock in a series of Z axis plunges.
Plunge Roughing is primarily used for machining pockets and external stock - in deep mould and dies for example. Long tools gain stability from a cutting force directed up the tool axis rather than as a side force.
Here are some key points, with associated tab indicated (if appropriate):
Material is removed as a series of concentric
passes (offsets of the boss profile for example). The tool works around
the pass with repeated plunges, stepping sideways by the 'Recommended
Stepover(%)' distance between plunges. Once the pass is complete the tool
advances by the 'Maximum Forward Step' distance (General
tab), to start the next pass.
Note that two step values are constrained to maximum values within
the cycle to avoid upstands of material being left between plunges.
Maximum recommended Forward Distance is limited by insert length.
The cycle is not optimised for centre cutting tools (though you could use such a tool). For example:
The advance between plunges cannot be more than the tool radius.
You need an approach strategy, such as a pre-drilled hole, for pocket regions (you need a centre point defined, though this need not correspond to an actual hole). (Approach tab)
The depth of a plunge cannot be deeper than the previous plunge within a region (so to rough out a doughnut you would need to machine the outside working inwards, then the hole in the middle working outwards).
To reduce tool wear and breakage, a 'Lead Out' move pulls the tool back from the cutting face before the Z-retract. You can set the angle (from the XY plane) and length of the Lead Out (Approach tab).
Roughing out a channel that's the same width of the tool is problematic as the Lead Out (see above) would be obstructed by the cusps left. You can use Minimum Radius (General tab) to prevent the tool entering narrow channels. (You could also set '0' for the length.)
The depth of the cycle is the same as other cycles (specified as a value or derived from model geometry). However full-depth plunges cannot always be made (for example because of swarf clearance problems in a pocket). In this case you can set a Cut Increment value, when there will be multiple passes round the profile, each increasing in depth by the cut increment. (Depth tab).
Using the 'Floor Approach' settings, the feedrate can be reduced towards the bottom of the plunge to compensate for the increased cutting area of angled inserts.(Approach tab).
Using 'Cut Increment Stand Off' (Approach tab) you can set the distance above the material floor left by the previous 'cut increment' at which to begin the helical ramp down to the next cut increment (if there is a ramp).