Milling Parameters Specific to Pencil Tracing

In addition to the common milling parameters, the following parameters control the tool path generated by a Pencil Tracing NC sequence:

Defines the number of pencil milling passes with constant step over. Constant Surface step over with an open profile produces the specified number of offsets on both sides of the open profile with the effect of a set of Parallel Pencil Milling passes. This strategy is used after finishing to tidy up the corners of the job, where there is a little too much material to be removed by standard Pencil Milling passes. Set the LIMIT_PASSES parameter a suitable value when creating multiple passes.

Set the contact angle range of the tool by setting the minimum and maximum contact angle. Boundaries are drawn around areas where the angle is within that range. For shallow area detection, the range should typically be in the range of 0 and 30 degrees. However, when surfaces are very close to the minimum or maximum angle, you may get an undesirably jagged edge so you can alter the range slightly. Alternatively, you can sometimes get rid of jagged edges by giving the boundary a small offset.

Use this parameter when the tool is in contact with the boundary areas. You can apply this extra thickness to the tool in addition to the set thickness when you need a tool that is slightly larger than the one you use to smooth corners. You can set it for Pencil Milling passes operations, or when editing passes using a stock model. With this parameter set, you can also make passes along fillets where the radius is greater than that of the cutter. See the topic, Example: Pencil Tracing Using Angular Limits.

This is the minimum distance by which the tool clears the surface during its rapid linking motion. All points of the tool, on both the tip and the side, avoid the surface by this distance. For minimal vertical retract motions, the tool lifts up to a height that ensures clearance. For shortest route motions, the tool is lifted up above the surface to ensure clearance, after it has gone past the clear surface within the specified distance.

This clearance is in addition to any thickness that you have already specified for the cutter. In particular, with a negative thickness, the clearance is above the reduced surface and not the real surface. Hence, you must set this value higher to prevent the tool from accidentally hitting the surface.

This parameter affects the path for shortest route retract. It specifies the distance the tool moves away from the surface before it enters rapid mode, which is the length of the lead-out of the machining pass. The distance is measured horizontally from the end of the lead out arc, to the point where the tool will clear the surface.

The values of theses parameters change the arc of the tool path between the lead-out and lead-in segments of the retract movements respectively. These parameters are applicable only when the RETRACT_OPTION parameter is set to the value SHORTEST_ROUTE. CURL_OVER_RADIUS defines the value of the arc for lead in movements and CURL_DOWN_RADIUS defines the value of the arc for lead out movements.

If you set the value of this parameter to YES, the stepover of the offsets of a profile is taken from the horizontal plane only, that is a 2D offset. The STEEP_STEP_OVER value is ignored. See the topic, Example: Pencil Tracing Using Horizontal Offsets.

Use this parameter to generate passes only in those areas inaccessible to a larger cutter. After setting this parameter to YES, you must select the previous tool.

Use this parameter to limit the number of passes that will be generated when machining the corners. The example below shows a result using LIMIT_PASSES = NO . Defining also a Previous Tool larger than the cutting tool. See the topic, Example: Pencil Tracing by Limiting Passes.

Using this parameter creates passes only where the cutter is in contact with the references. To machine areas that include non-contact areas, do not use this parameter. See the topic, Example: Pencil Tracing for Contact Areas.

Use this parameter to reverse the direction of passes. For bi-directional passes each pass is machined in the opposite direction to the previous pass.

When moving between the end of one pass and the beginning of another, the cutter is either on the surface or it is in retraction, depending on the distance it has to travel. The parameter here controls the point where the decision between the two states is made. If the distance between the end point of one pass and the start point of another is less than this value, the cutter stays on the surface. If the distance is greater, the cutter retracts to the clearance plane. See the topic, Example: Cutter Placement During Pencil Tracing.

Use this parameter to control the ramp connections between each pass along the references. This parameter has the following values:

• With Angle—A direct connection is made between each pass along the surface in a straight line at this preferred angle.

• Tangent With Angle—A direct connection is made between each pass along the surface in an angled linking motion. This connection is a smooth s-curve.

• Spline Curve—A curved connection is made between each pass along the surface. The movement is fluid and there are no sharp corners so there is little change of speed of the cutter throughout the length of the link.

Use this parameter to set the length of the machining passes to be cut. Passes shorter than the specified length are not included in the tool path.

Use this parameter to define the trimming style by setting the value to MINIMUM or FULL. When a lead arc is added to a horizontal machining pass, the length of the pass trimmed off will be at most the radius of the arc. However, when adding an arc to a steep finishing pass, the length of pass trimmed that is, the trimming distance is much greater. This is likely to remove excessive amounts of machining pass and leave large areas of material uncut.

Using this parameter puts a limit on the trimming distance. If the amount trimmed exceeds the value specified, then no arc is used, and instead the whole pass is machined, and a straight vertical motion added.

Use this parameter to increase the height of the start of the ramp.

Use this parameter to remove sharp jumps on surfaces adjacent to steep areas. Sometimes at the end of a pass, where one surface is adjacent to another at a very steep angle, there is a sharp jump. This can happen where the cutter touches a steep wall and is lifted to the top, or where it falls off a high ledge and drops to the bottom. When you use this parameter to remove spikes, these sharp jumps are removed.

When you set the value to end, only spikes at the end of the passes are removed. There is no spike removal on a looped pass if this option is active, as there is no end. In this case you can deselect the option and remove spikes from the middle of passes.

Spikes or jumps with an angle greater than the MAX_SPIKE_ANGLE are edited from the tool path. The angle is measured from the horizontal plane.

Use this parameter to specify the maximum length of area to be edited on regions affected by spikes. You can trim off any small horizontal areas left at the top or bottom of the spike.

Use this parameter in conjunction with the SURFACE_RAMP_OPTION, parameter to capture the value of the ramp angle to be used in calculations.

This parameter defines the retract style to apply to the pencil milling passes. This parameter has the following values:

• ALWAYS—The cutter moves vertically up to the clearance plane, moves along this level in a straight line, and drops down vertically to the start of the next pass.

• SHORTEST_ROUTE—The cutter takes a direct route from one pass to another clearing the surface and incorporating a curve to speed progress. The minimum height of the retract movement is controlled by the CLEAR_BY parameter, and the shape is controlled by the RETRACT_SMOOTH_RADIUS, CURL_OVER_RADIUS, and CURL_DOWN_RADIUS parameters.

• MINIMAL_VERTICAL—The cutter moves vertically to the minimum Z-height needed to clear the surface, moves along this plane in a straight line and drops down vertically to the start of the next pass. The minimum height of the retract is controlled by the CLEAR_BY parameter.