Module 4: Cutting Operations & Troubleshooting Assessment Quiz

Module: U4M4 - Cutting Operations & Troubleshooting Duration: 25 minutes Passing Score: 70% Format: Multiple choice and scenario-based

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During a CNC routing operation, you hear a high-pitched squealing sound. What is the most likely cause?

The feed rate is too slow relative to spindle speed, causing the tool to rub instead of cut

The spindle speed is too slow

The dust collection system is clogged

The material is too thick for the machine

Submit

Explanation: A high-pitched squeal indicates friction from rubbing rather than proper chip formation. This occurs when chip load is too low (feed too slow or RPM too high). The fix is to increase feed rate or decrease spindle speed.

What is the correct operator response when a cutting tool breaks during operation?

Press E-stop immediately, wait for all motion to stop, then inspect for damage

Pause the program, replace the tool, and resume from the current position

Reduce feed override to 10% and let the program finish

Turn off the spindle but let the axes finish their movement

Submit

Explanation: A broken tool requires an immediate E-stop. Continuing to run with a broken tool risks workpiece ejection, machine damage, and operator injury from fragments. After full stop, inspect the tool, workpiece, and machine before any further action.

What causes "fuzzy" or torn edges when routing plywood?

Using an upcut bit that pulls the top veneer fibers upward, causing tearout

Spindle speed is too high

The material is too cold

The spoilboard is too thick

Submit

Explanation: Upcut spiral bits pull chips upward, which tears the top veneer layer of plywood. Using a downcut bit (for clean top surface), compression bit (for clean top and bottom), or scoring the top with a shallow pass first addresses this issue.

What is "tool deflection" and how does it affect cut accuracy?

The bending of the cutting tool under cutting forces, causing the cut to be offset from the programmed position

The axial movement of the tool in the collet

The thermal expansion of the tool during cutting

The wear of the tool edge over time

Submit

Explanation: Cutting forces push the tool sideways, causing it to bend (deflect). This makes the actual cut position different from the programmed position. Deflection is worse with longer tool stick-out, smaller tool diameters, deeper cuts, and higher feed rates. It increases with the cube of unsupported length.

When cutting aluminum on a CNC router, which of the following is most critical?

Using a single-flute end mill with adequate chip clearance and cutting fluid

Using the highest spindle speed available

Taking full-depth cuts to minimize passes

Using a compression bit for clean edges

Submit

Explanation: Aluminum requires excellent chip evacuation to prevent chip re-cutting and welding. Single-flute (O-flute) bits provide maximum chip clearance. Cutting fluid (WD-40, isopropyl alcohol, or specialized aluminum cutting fluid) prevents chip welding and reduces heat. Compression bits are for wood laminates only.

A student notices their pocket cut is 0.015" shallower in the center than at the edges. What is the most likely cause?

The spoilboard is not flat — it has a high spot in the center relative to the gantry plane

The spindle speed is too high

The material is too soft

The G-code has a programming error

Submit

Explanation: If the spoilboard surface is not parallel to the gantry's XY plane, Z-depth will vary across the work area. A high spot in the spoilboard (or a dip in the gantry) makes the center of the pocket appear shallower. Surfacing the spoilboard with a flattening bit resolves this.

What is "chip recutting" and why is it a problem?

When chips are not evacuated and are re-cut by the tool, causing heat buildup and poor surface finish

When the tool cuts the same profile twice due to a programming error

When broken tool fragments scratch the workpiece surface

When chips from one operation contaminate another part on the bed

Submit

Explanation: If chips remain in the cut path (poor evacuation), the tool re-cuts them on the next pass. This generates excessive heat, dulls the tool rapidly, and creates a rough surface finish. Proper dust collection, adequate flute space, and upcut geometry help evacuate chips.

What is the recommended action when cutting is complete but tabs are still holding the part?

Remove the part from the machine, then cut tabs with a hand tool (flush-cut saw, chisel, or oscillating tool)

Run a second program to cut through the tabs at high speed

Break the part free by twisting it with pliers while it is still on the machine

Use a hammer to knock the part free from the tabs

Submit

Explanation: Tabs should be removed carefully after the part is off the machine (or on the machine with spindle off). A flush-cut saw, sharp chisel, or oscillating multi-tool provides clean tab removal. Forcing parts free can crack the material or damage the cut edges.

During a long CNC routing job (45+ minutes), what should the operator monitor continuously?

Chip formation, cutting sound, material hold, dust collection, and spindle temperature

Only the computer screen for error messages

Only the feed rate display

Nothing — the machine is automated and does not need monitoring

Submit

Explanation: CNC operation requires continuous operator monitoring. Changes in sound indicate tool wear or parameter issues. Chip formation reveals cutting effectiveness. Material hold must be verified throughout. Dust collection prevents hazards. Spindle temperature (especially VFD) should stay within limits. Never leave a running CNC unattended.

What causes "chatter marks" — evenly spaced ridges on the cut surface?

Vibration caused by resonance between the tool, workpiece, and machine structure

The G-code has too many decimal places

The spoilboard is contaminated with adhesive

The dust collection suction is too strong

Submit

Explanation: Chatter is a self-excited vibration that occurs when cutting forces excite a natural frequency of the tool, workholding, or machine structure. It produces characteristic evenly-spaced marks. Fixes include: changing RPM (to shift frequency), reducing depth of cut, improving workholding rigidity, shortening tool stick-out, or using a different number of flutes.

A student's profile cuts are consistently 0.010" oversized. The most likely cause is:

Tool deflection pushing the tool away from the cut line during profile passes

The tool diameter is incorrectly entered in the CAM software

The spindle speed is too high

The material has expanded due to moisture

Submit

Explanation: While an incorrect tool diameter in CAM could also cause this, consistent oversizing on profile cuts is classic tool deflection. Cutting forces push the tool away from the material, making outside profiles larger and inside profiles smaller than programmed. Reducing depth of cut, feed rate, or tool stick-out reduces deflection.

When is it appropriate to use the feed override control during a cut?

To reduce feed when the cut sounds aggressive, or to gradually increase from 50% at the start of a new job

Never — feed should always match the programmed value

Only to speed up the cut when you are in a hurry

Only when cutting metal

Submit

Explanation: Feed override is a real-time safety tool. Starting at 50% override on new jobs lets the operator verify parameters are safe before running at full speed. If cutting sounds or looks aggressive (chatter, excessive forces), reducing override provides immediate relief while the operator diagnoses the issue.

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Last Updated: 2026-03-19