2D Milling-Pocket Contour Parallel XI

Pocket definitions

Pockets are defined as 2D, top view representations of a shape to be cut out of surrounding material. The shape is a closed chain and can be selected by Shift-Select or forward selected with CTRL-W. The direction of selection of the pocket perimeter will determine whether the pocket is cut with a climb or conventional milling pattern. To cut with climb milling, select in a counter clockwise direction(CCW), and for conventional milling, select in a clockwise direction(CW). Generally a pocket is cut with a flat end cutter, but other geometries can also be specified.

A pocket can have multiple internal shapes, each also a closed chain. These are called islands. The islands cannot overlap each other, and cannot overlap the outer contour. Each must be fully contained and separated from the outer contour and from each other.

Above left, an elliptical pocket, with a rectangular island, is selected in a CCW direction.

Above right shows a rectangular pocket with a circular and an elliptical island, not selected.

Practical considerations for a pocket require that the distance between each island and the outer wall and between each other be designed to be larger than the diameter of the end mill plus any finishing stock. Drawing an offset curve around the selected geometry can easily test this. Any overlapping of the contours will indicate that either the geometry will have to be altered, or else that a smaller tool is required to fully clean out the islands from the surrounding contour. When the pocket above with two islands is offset by .0625 inches (1/8 cutter), it results in this drawing (Draw-Other Curves-Offset)

However, when offset by .125 the following results:

Note the merged offset contours between the upper right island and the outer contour. This test indicates that a 1/8-inch diameter end mill will fully clean out the pocket, but that a ¼ inch will not. The size-testing offsets can be removed by using the Edit-Undo function. This will return the geometry to the selected condition and the pocketing function can then be selected.

Nested island pockets are permitted, provided that the internal pocket within an island is fully isolated from the surrounding island and is also defined as a closed chain. An example of such a construction would be the inside of the letter A, provided the A was an island within a larger contour.

To create the pocket toolpath, NC-2D milling-Pocket Contour-Parallel

Select Tool (See NC-2D Contouring for explanation of tool selection.)

Roughing

Roughing Stepover % – This is the maximum percent of the cutter diameter that will be used when calculating the tool paths. Setting this value above 55-65% may result in some material left behind after the cut. This depends on the interactions of the geometry design and the cutter size. Simulation can be used to test multiple settings. (Alternately, if the jobs process is not used, or after the job is exploded, a line width attribute, equal to the cutter diameter and viewed from the top view will give a very quick snapshot of the cutting condition without waiting for the full simulation to be completed.) A larger value for roughing step over percent will result in a heavier cutter load and this may result in a more efficient pocketing cut. When cutting some materials like wood, small vertical residues may be removed simply as a result of cutting side pressure. In metals, it is unlikely that it would be desirable to have any material left behind. However sometimes in metals, it is useful to cut through the material, leaving a contoured hole. In this case a larger percentage step over would still leave the desired results.

Roughing Stock to Leave – this value is a distance within which the cutter will not be programmed. Depending on the material a finish pass may or may not be required with the contour parallel pocket. If a finish pass is needed for sizing or surface finish considerations, a small distance can be specified in this value. If no stock is required, enter zero for Stock to leave.

Z-Movement

Pocket Depth – This is the total depth of cut to the bottom of the pocket.

Maximum depth per roughing pass – Depth of cut per roughing pass. If one cut to depth is desired, enter a value greater than or equal to the pocket depth. If multiple passes are desired, enter the depth per pass. If a finish pass is desired, enter a value which will make multiple passes, leaving a small amount for the finish. For example to cut a .25 deep pocket with two large passes and a .010 finish pass across the bottom of the pocket, .25 -.010 would be .24 for the heavy roughing passes. If two heavy passes were desired, divide .24 by 2 = .120. Use this value for the Maximum depth per pass to create 3 passes. The first pass at Z=-.120, the second pass at Z= -.140, and the third at Z=-.250.

Z-Movement Connections (See contouring for explanation of tool selection.)

Finish – The finish pass is optional. Uncheck the box in front of Finish Distance to create the pocket toolpath, without a finish pass.

Finish Distance – If the box is checked, enter either the desired finish pass stock distance that will be left behind after the finish pass is completed. This distance is very similar to the finish pass on roughing. However, by default the pocketing routine is set to use controller cutter compensation. If G41/G42 cutter compensation is not used, enter the cutter RADIUS to cut to the desired size.

Maximum depth per finish pass – If multiple passes are desired for the finishing toolpath, enter the desired depth per pass. Use the same calculation for a finishing allowance as used for roughing depth per pass if a final finish pass different from the initial passes is desired.

Approach and Depart – See NC-2d Milling-Contouring for an explanation of approach and depart. The finish pass will have a teardrop approach and depart by default in preparation for the use of cutter comp. Disable the approach and depart is this is not desired.

Pocket Start Point

Pocket start points can be specified for contour parallel pockets. Specify a start point and outlines. The first move into the pocket will occur at the specified point followed by motion toward the contour parallel normal start point, and then the rest of the material is removed using the pocket-contour parallel method. This start point is only for the roughing passes. The finishing start-point is set by the approach and departs values.

JOB Tab

The Job tab on the Contour parallel pocketing dialog permits naming of the job step and modification of the tool technology provided by selection of the tool.

Ramp/Helix Tab

The Ramp Helix tab controls the method used to plunge into the material during the roughing passes. It does not apply to finishing.

Selecting Straight Descent will plunge straight into the workpiece at all times that a vertical descent is calculated.

Selecting Linear Ramp will plunge into the workpiece at the specified angle. This plunge is calculated along the contour of cut and will not interfere with any islands or perimeter geometry.

15 degree ramping:

Helix Ramping is a series of linear movements that approximate a circular helix. The angle, radius, tolerance and rotational direction of cut can be specified on the dialog. This plunge type is also checked for interference with island and perimeter geometry.