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CNC fundamentals

Change a bit and measure its length

Watch a short bit leave the collet, fit a longer bit and measure it on a fixed bit setter.

About 6 minCadivari 0.3.0Watch and try

Useful first: Understand safe clearance · Recognise the main cutter shapes

A bit setter detects the tip at a fixed location. Comparing the new measurement with the reference lets the controller account for a different installed tool length while preserving the established work zero. It does not measure diameter or find the stock surface. The animation’s 25 mm and 50 mm stick-outs make the difference visible; they are illustrative, not recommended mounting lengths.
A bit setter detects the tip at a fixed location. Comparing the new measurement with the reference lets the controller account for a different installed tool length while preserving the established work zero. It does not measure diameter or find the stock surface. The animation’s 25 mm and 50 mm stick-outs make the difference visible; they are illustrative, not recommended mounting lengths.

A bit setter detects the tip at a fixed location. Comparing the new measurement with the reference lets the controller account for a different installed tool length while preserving the established work zero. It does not measure diameter or find the stock surface. The animation’s 25 mm and 50 mm stick-outs make the difference visible; they are illustrative, not recommended mounting lengths.

Try it in Cadivari

  1. Watch the reference measurement

    The short gold bit touches the fixed setter and retracts. Its reference measurement belongs to the work Z already established for this setup. The setter is separate from the stock and is not a stock-zero probe.

  2. Watch the manual change

    The machine parks and waits with the spindle stopped. The short bit moves down out of the collet, leaving it visibly empty. The longer green bit is then inserted and secured. On a real machine, follow its tool-change prompts and spindle isolation procedure before touching the cutter.

  3. Compare the second measurement

    The longer bit touches the same setter while its collet remains higher. The controller records the difference and updates its tool-length compensation. The final view shows the longer bit at the same tip height above the stock, with the previous collet height drawn as a dashed gold mark.

  4. Assign the actual cutters in Cadivari

    Open a preview job with two existing operations. Verify each physical cutter in Tool library, then use each operation’s Cutter row to assign the correct record. Check the exact diameter and the visible T number in the stage list; A and B in the animation are illustrative labels.

  5. Review the change stages

    Open Job sequence & output. Preserve the operation order and keep any final outside cutout last. Select Carbide Motion to review a combined file with M6 tool-change stages. Carbide Motion handles the physical change and BitSetter cycle; Cadivari does not connect to or probe the machine.

  6. Check the pause after measurement

    Inspect the program after each M6. Cadivari restores G90 and raises to the configured Service / park Z before an M0 pause for manual router start. M0 pauses the program but does not itself stop or start the router. Review tool identity, length measurement and clearance before any real resumption.

  7. Recognise the separate-file workflow

    Select Separate files to compare the numbered cutter stages without M6. For that workflow, the operator re-establishes Z or uses the sender’s verified tool-length procedure between files while keeping XY zero. This exercise ends at preview.

Over to you

A small exercise

Scrub to the empty collet, then to each setter contact. Identify the longer bit and explain why its collet touches off at a higher position. In a preview job, find two cutter stages and compare Carbide Motion with Separate files.

What you should see

The two bits have visibly different stick-outs. Both contact the same setter surface, and the 25 mm illustrative difference changes the collet height while the tip retains the work Z reference. Cadivari’s stage list and exported mode agree with the intended controller workflow.

Things to look out for

  • A bit setter measures installed length, not diameter, cutter identity or stock zero. The cutter record and physical bit must still agree.
  • Changing how far a bit sits in the collet changes its measured stick-out. Remeasure through the controller’s supported workflow after a change.
  • The illustrated machine travel and lengths are explanatory. Actual clearance, collet engagement and probing steps depend on the machine and cutter.
Check your understandingDoes a longer replacement bit require changing XY work zero

No. With a verified tool-length workflow and unchanged workholding, the controller accounts for the different length in Z while preserving the job’s XY reference. A length measurement does not identify the cutter or measure its diameter.

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Go deeper in the knowledge base

Instructions checked against the Cadivari 0.3.0 source and knowledge base on 2026-09-16. Lesson revision 1.