Before you begin
A stock drawing, a toolpath preview, the machine manual, and manufacturer guidance for your chosen holding method.
What this lesson covers
- Map hardware against the complete tool and holder envelope.
- Identify when a part or offcut loses restraint.
- Separate repeatable location from adequate holding force.
Recommended preparation
01 / Key concepts
How it works
Workholding keeps the material in place; work zero tells the machine where the job begins. Both must match the CAM setup to produce accurate parts, including during the final cut when pieces separate.
- Fixture
- A device that locates and supports work for a defined operation.
- Release plan
- The planned way the finished part and offcuts remain controlled as cuts separate them.
Choose the holding method for the operation
Screws, clamps, tabs, vacuum, spoilboard tape, fixtures, and pins solve different problems. Select a method that resists the cutting forces without putting hardware in the tool path.
Treat zero as a physical location
Mark the stock reference, decide whether zero is a corner, center, top, or spoilboard surface, and confirm that the drawing, CAM setup, and machine use that same reference.
Plan for the last part of the cut
Small parts, through-cuts, and thin offcuts can shift when they are released. Use appropriate tabs, onion skin, fixtures, or sequence planning to keep the final cuts controlled.
Key points
- The part must stay controlled through the last cut, not only the first.
- Hardware clearance belongs in the CAM plan before the toolpath is generated.
- Mark the physical work origin and check it against the CAM setup.
02 / Worked example
Workholding as the cut progresses
A panel has an internal pocket and an outer profile. No clamp clearance, tab size, or vacuum capacity is prescribed here; those depend on the actual system.
| Stage | What changes | What to verify |
|---|---|---|
| Before machining | Stock is one piece | Location, support, hardware, and clearance |
| Pocket operation | Material and support are removed | Remaining restraint and tool access |
| Outer profile | Part can separate from surrounding stock | Part and offcut control through the last pass |
| Unload | Cutting has ended | Documented safe stop before access |
03 / Workshop exercise
Apply the method
Work through the drawing or setup review first, then use a sample that matches your project. Check the equipment and safety requirements above before starting any machine work.
- Sketch the toolpath and the complete cutter-and-holder clearance envelope on the setup plan.
- Check hardware and fixture clearance separately from the CAM tab or other release-control strategy; tabs are intentional part connections, not clamps to place outside the path.
- Have a trained operator review the release plan before a controlled scrap test. Follow machine safeguards and record whether the part and offcuts stayed controlled through the final pass.
Common mistakes
- Placing a screw where the cutter will travel.
- Forgetting that a small part can release near the end.
- Using an unmarked or inconsistent stock reference face.
Take it further
Annotate a toolpath preview at the moment each piece separates. Document the holding assumption that remains true at every stage.
Workshop checklist
Use this topic checklist alongside your machine’s full setup procedure.
- Map clamps, screws, tabs, or fixtures before CAM.
- Confirm toolpaths avoid all hold-down hardware.
- Mark the stock reference face and origin.
- Verify X, Y, and Z zero against the drawing.
- Plan how small parts remain secure during through-cuts.
04 / Review questions
Review the key decisions
Consider each question, then compare your answer with the explanation. Return to the worked example whenever you need it.
1. A screw is outside the drawn part. Is it necessarily outside the machining envelope?
View hint
The cutter is not the only object that moves.
View explanation
No. Account for the complete cutter and holder, approach moves, retracts, and the actual toolpaths. Use the machine-specific clearance procedure.
2. Will a repeatable locating fence by itself guarantee the part cannot move?
View hint
A locating fence positions the part; consider what resists the cutting force.
View explanation
No. A location reference positions the work. The holding method must still resist the operation and control release, using appropriate system guidance.
05 / Project notes
Notes for your next project
Check off the topics you have reviewed and record anything useful for your next build. This tracks your learning progress; use your equipment’s setup procedure for machine checks.
Record: Holding method, fixture layout, zero point, tab/onion-skin plan, and how the final parts released.
No notes recorded. Use this space for your observations.
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Check each topic above to mark the lesson as reviewed. You can browse any lesson at any time.
Related calculators
Use your project measurements and costs in the calculators below. Check the results against the stock, equipment and requirements of the job.
Practice with a complete project
Apply the lesson to measured dimensions, then keep the drawing, material list and build checks together.
Sources & further study
WoodWorkCalc writes the exercises and illustrative examples. Named historical cases are attributed separately. These sources support the principles identified in the lesson; their publishers do not endorse WoodWorkCalc. Guidance and platform features can change. Sources retain their own copyright and licensing terms.
- ShopBot Tools — CNC Documentation (opens new tab)
Manufacturer's documentation directory for model-specific CNC setup, software, and accessories. Use the manual for your own machine; ShopBot procedures are not universal.
ShopBot Tools. Support Resources. Accessed September 10, 2026.