Summary
Start Side in VoluMill is a preference, not a command that forces an entry point. VoluMill first selects the fastest, most efficient start location for the calculated toolpath. The selected Start Side affects the result only when two or more candidate start points are equally optimal.
A shape with one best start point, such as many square or asymmetric pockets, may show no change when Start Side is edited. A rectangular slot can have two equally advantageous ends; in that case, VoluMill chooses the candidate closest to X+, X-, Y+, Y-, or the specified Custom value. This can help make repeated entries more consistent or favor a side that improves chip evacuation on a horizontal machine.
Table of Contents
Before You Begin
Open the GibbsCAM part and save a backup copy before changing VoluMill process settings.
Generate the current operation and note the existing plunge or ramp location before changing Start Side.
Confirm that the correct geometry or solid, stock, tool, plunge type, depths, allowances, and machining coordinate system are active.
Identify the practical reason for preferring a side, such as chip evacuation, consistent access, operator visibility, or fixture clearance.
Interpret X+, X-, Y+, and Y- relative to the active Machining CS, not merely the current screen view.
Use a shape likely to have more than one equally efficient candidate when testing the control, such as a rectangular slot with comparable access at both ends.
Plan to simulate and review the posted program after any entry-location change.
Important: Start Side never overrides VoluMill's efficiency calculation. If one candidate is faster or otherwise more optimal, VoluMill uses that point regardless of the selected preference.
How Start Side Is Applied
VoluMill evaluates possible entry locations before applying the preference. Start Side is consulted only after the calculation finds multiple candidates with the same optimal result. It then selects the tied candidate closest to the preferred axis side or Custom value.
Figure 1 - Start Side choices listed under VoluMill Plunge Controls.
Procedure
Step 1 - Define the Preferred Side
Identify the physical side from which entry would be preferable for the setup.
Activate the operation's Machining CS and confirm which axis direction corresponds to that physical side.
For a horizontal machine, consider whether favoring the lower eligible side would allow chips to fall away from the entry and cutting region.
Treat the preference as optional optimization; do not use Start Side as a substitute for fixture avoidance, clearance planes, or a required entry point.
Expected Result
The desired physical side is mapped to X+, X-, Y+, Y-, or an appropriate Custom value in the active Machining CS.
Step 2 - Evaluate Whether the Shape Can Respond
Review the selected pocket, slot, or region and identify plausible entry areas.
Expect little or no response when the shape, stock, islands, tool size, or access creates one clearly best start point.
Use a rectangular slot or another shape with comparable access at two locations when validating the feature.
Generate a baseline operation and record the start point so the effect of the setting can be compared.
Expected Result
The test geometry has either one known optimal start point or multiple plausible tied candidates, and a baseline result is available.
Step 3 - Set Start Side in the VoluMill Process
Open the VoluMill process and locate Plunge Controls on the VoluMill page.
Confirm the required Plunge Type and its entry parameters. Start Side is available with the VoluMill plunge types.
Set Start Side to X+, X-, Y+, or Y- according to the active Machining CS.
When a directional side is insufficient, select Custom and enter the applicable starting value.
Generate the operation without changing unrelated toolpath parameters so the comparison remains meaningful.
Expected Result
The process contains the intended Start Side preference and has been regenerated under otherwise comparable conditions.
Step 4 - Compare Eligible and Ineligible Shapes
On a shape with a single optimal point, change Start Side to the opposite side and regenerate.
Confirm that the start location may remain unchanged because the preference cannot override the unique optimal candidate.
Repeat the test on a rectangular slot or another shape with two equally efficient entry candidates.
Switch between opposing Start Side choices and regenerate after each change.
Confirm that VoluMill selects the tied candidate closest to the chosen side while preserving the efficient toolpath strategy.
Expected Result
The comparison demonstrates that Start Side breaks an efficiency tie but does not force a less efficient start point.
Step 5 - Apply the Preference to Production Geometry
Restore the production part, tool, stock, depths, allowances, and active Machining CS.
Choose the Start Side that best supports the setup objective, such as directing eligible slot entries toward the lower side of a horizontal-machine setup.
Generate every affected operation and inspect the actual start point for each region; do not assume all features have the same candidate set.
If a feature ignores the preference, accept the optimal result or revise the machining strategy rather than attempting to force an inferior point with this control.
Expected Result
Every eligible region uses the preferred tied candidate, while regions with a unique optimum retain VoluMill's fastest start point.
Step 6 - Simulate and Verify
Run Op Simulation and review each plunge or ramp, transition area, link, high-feed move, and cutting region.
Verify clearance from the part, stock, fixture, tool holder, and machine components at the selected start locations.
Confirm that the preferred side actually supports the intended chip-flow or access objective under the real machine orientation.
Post the complete operation sequence and confirm entry coordinates, depths, feeds, speeds, clearances, and operation order.
Resolve every discrepancy and follow the shop's approved single-block, dry-run, and prove-out procedure before production machining.
Expected Result
The selected preference is used only where equally optimal choices exist, and all generated entries are safe in simulation and the posted program.
Expected Result
VoluMill continues to select the fastest available start point for every region. When multiple candidates are equally optimal, the operation uses the candidate closest to the selected X+, X-, Y+, Y-, or Custom preference. Shapes with one optimal point remain unchanged, while eligible slots or repeated features begin from the preferred side without sacrificing calculated efficiency.
Best Practices
Use Start Side to express a preference, never as a required entry-point command.
Verify the active Machining CS before interpreting X+, X-, Y+, or Y-.
Test the feature on a rectangular slot or another shape likely to have equally optimal candidates.
Change only Start Side during comparison tests so other parameters do not obscure the result.
Regenerate after every Start Side, geometry, stock, tool, or depth change.
Inspect each pocket or slot independently; similar-looking features can have different optimal candidates.
Use the preference for practical goals such as chip evacuation only after confirming the machine's real orientation.
Use fixture avoidance, solids, clearances, and simulation for safety; Start Side does not protect a required side from collision.
Review the posted program because a preferred graphical start point must still be verified in CNC output.
Troubleshooting
Problem: Changing Start Side does not move the VoluMill entry.
Possible Causes
The shape has only one optimal start point.
One candidate is faster or more efficient than the candidate nearest the preferred side.
The operation was not regenerated after the preference changed.
Resolution
Regenerate the operation and confirm the selected value. If the point remains unchanged, test with a rectangular slot or another known tie case. Accept that Start Side has no effect when the current shape has a unique optimal candidate.
Problem: The entry moves to the opposite physical side from the one expected.
Possible Causes
The active Machining CS axes do not match the current screen orientation.
The wrong X or Y sign was selected.
A different coordinate system became active when the operation was regenerated.
Resolution
Display and verify the active Machining CS, map the physical side to its actual axis direction, select the correct sign, and regenerate the operation.
Problem: Some rectangular slots follow the preference while others do not.
Possible Causes
Stock, boundaries, islands, nearby walls, or prior material removal make the candidate sets different.
Tool access or ramp space creates a unique optimum in some slots.
The slots use different geometry, depths, processes, or coordinate systems.
Resolution
Inspect each slot's inputs and baseline entry separately. Correct unintended differences, regenerate, and use Start Side only for features that still have equally optimal candidates.
Problem: Custom Start Side does not place the entry at the entered value.
Possible Causes
Custom supplies a preference value rather than an exact forced coordinate.
No optimal candidate exists at the entered location.
A different candidate remains more efficient or is the only valid choice.
Resolution
Treat the Custom value as a reference for selecting among tied optimal candidates. If an exact start point is mandatory, evaluate a different approved machining strategy; Start Side cannot force that coordinate.
Problem: The preferred entry is poor for chip evacuation on the horizontal machine.
Possible Causes
The chosen axis side is not the physical lower side in the active machine setup.
The feature has one optimal point and therefore ignores the preference.
Actual chip flow depends on coolant, gravity, pocket geometry, and the complete cutting sequence.
Resolution
Verify the machine orientation and Machining CS, select the axis side that corresponds to the desired physical location, and simulate the complete sequence. Use shop-approved coolant and chip-control practices in addition to Start Side.
Problem: The entry changes after another VoluMill parameter is edited.
Possible Causes
The geometry, tool, stock, depth, plunge settings, or minimum-radius values changed which start point is optimal.
A former tie no longer exists, or a new set of tied candidates was created.
The operation was regenerated using different active inputs.
Resolution
Re-evaluate the generated candidate behavior after every material toolpath change. Restore the intended inputs, confirm Start Side, regenerate, and verify the new entry rather than assuming the earlier preference result will remain.
Additional Information
Start Side scope: The control affects the choice among equally optimal entry candidates. It does not set cutting direction, Climb or Conventional behavior, toolpath order, a fixed XY entry point, or collision avoidance.
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Keywords
GibbsCAM, VoluMill, Start Side, Start Point, Entry Point, Plunge Controls, Plunge Type, X Plus, X Minus, Y Plus, Y Minus, Custom Start Side, Optimal Start Point, Rectangular Slot, Square Pocket, Horizontal Mill, Chip Evacuation, Machining CS