Module 2: Assessment Quiz

Module: U1M2 - Machine Setup and Calibration Duration: 20-30 minutes Passing Score: 70% (10 of 14 questions) Format: Multiple choice, matching, and scenario-based

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Questions 1-4: Bed Leveling Fundamentals

What is the correct sequence for manual bed leveling?

Check all four corners, then center, then re-check corners

Only check the center point

Check corners once and print immediately

Use auto-level and skip manual verification

Submit

Explanation: Bed leveling requires checking all corners and center because adjusting one corner affects others. Re-checking ensures convergence to proper level. A single pass is almost never sufficient for achieving the ±0.1mm tolerance required for reliable first layers.

What is the acceptable tolerance for bed leveling on a typical FDM printer?

±1.0mm across the entire bed surface

±0.5mm across the entire bed surface

±0.1mm across the entire bed surface

±0.01mm across the entire bed surface

Submit

Explanation: The standard tolerance for bed leveling is ±0.1mm. Since typical first layer heights are 0.2-0.3mm, a deviation of 0.1mm represents a 33-50% change in first layer thickness. Tighter tolerances (±0.01mm) are impractical for consumer printers; looser tolerances (±0.5mm+) cause adhesion failures.

When using a feeler gauge for bed leveling, what thickness gauge should be used and what sensation should you feel?

0.1mm gauge; slight drag when sliding between nozzle and bed

0.5mm gauge; no resistance when sliding

0.1mm gauge; no resistance at all (gap should be larger than gauge)

0.2mm gauge; gauge should not fit between nozzle and bed

Submit

Explanation: A 0.1mm feeler gauge (approximately the thickness of a sheet of paper) is the standard tool for manual leveling. The gauge should slide between the nozzle and bed with slight friction — not free-floating (gap too large) and not stuck (gap too small). This ensures the nozzle-to-bed distance matches the intended first layer height.

A BLTouch (or similar inductive/capacitive probe) automates bed leveling. What does it actually measure?

The exact temperature of the bed surface

The flatness of the print surface coating

The distance between the probe and bed at multiple points, creating a mesh compensation map

The levelness of the frame relative to gravity

Submit

Explanation: A BLTouch probe measures the Z-distance between the probe tip and the bed surface at a grid of points (typically 9-25 points). The firmware creates a mesh map of the bed surface and compensates for unevenness during printing by adjusting Z-height in real-time. It does not replace mechanical leveling entirely — the bed should still be roughly level before probing.

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Questions 5-7: Filament Loading and Temperature

What is the correct procedure for loading filament into an FDM printer?

Push filament into the cold end and turn on the heater

Preheat the nozzle to the filament's printing temperature, then insert filament until it extrudes cleanly

Load filament at room temperature and let the printer heat it gradually

Force filament through the nozzle at any temperature using pliers

Submit

Explanation: The nozzle must be preheated to the material's printing temperature before loading. Cold filament pushed into a cold nozzle will jam. Once at temperature, filament is fed through the drive gear and into the hot end until clean, consistent extrusion is visible — this purges any residual material from the previous print.

A student is switching from ABS (print temp 240°C) to PLA (print temp 200°C). What is the correct filament change procedure?

Remove ABS at room temperature, then load PLA at 200°C

Remove ABS at 200°C, then load PLA at 200°C

Remove ABS at 240°C, purge with PLA at 230°C, then reduce to 200°C for printing

Remove ABS at 240°C, immediately load PLA at 200°C

Submit

Explanation: ABS must be removed at its printing temperature (240°C) to ensure it flows out cleanly. PLA should then be loaded at an intermediate temperature (~230°C) to flush any remaining ABS residue from the nozzle. Once the extrusion runs clean PLA, the temperature can be reduced to 200°C for printing. Skipping the purge risks ABS contamination in the PLA print.

What is thermal runaway protection, and why is it critical?

It prevents the printer from cooling too quickly during a print

It monitors bed adhesion temperature for optimal first layer

It detects when a heating element is on but the thermistor reads no temperature increase, shutting down to prevent fire

It limits the maximum print speed to avoid overheating the stepper motors

Submit

Explanation: Thermal runaway protection is a firmware safety feature that monitors whether the heater cartridge is producing expected temperature increases. If the thermistor fails or disconnects, the heater could run at full power indefinitely, reaching temperatures that ignite surrounding materials. Thermal runaway protection detects this mismatch and immediately shuts off the heater, preventing fire. Printers without this feature (or with it disabled) are a serious fire hazard.

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Questions 8-10: First Layer Optimization

A student's first layer appears translucent and paper-thin, with visible gaps between extrusion lines. What is the most likely cause?

Nozzle temperature is too high

Print speed is too fast

The nozzle is too far from the bed (Z-offset too high)

The filament diameter is too small

Submit

Explanation: When the nozzle is too far from the bed, the extruded plastic is not pressed into the surface adequately. This causes thin, translucent lines with visible gaps. The correct first layer should appear as slightly squished, overlapping lines with no gaps. The fix is to decrease the Z-offset (bring nozzle closer to bed) in small increments (0.05mm at a time).

What does "first layer squish" refer to, and what is the ideal appearance?

The slight compression of the first layer against the bed, producing flat, wide lines with no gaps and slight overlap between adjacent lines

The sound the printer makes when the first layer is pressed too hard

The warping of the first layer edges as they cool

The excess material that oozes from the nozzle before printing begins

Submit

Explanation: First layer squish is the controlled compression of the initial extrusion against the build surface. The nozzle should be close enough that extruded plastic is pressed flat (wider than the nozzle diameter) and adjacent lines slightly overlap, creating a continuous, well-adhered sheet. Too much squish causes plastic to build up on the nozzle; too little causes gaps and poor adhesion.

A student observes that their first layer has ridges and the nozzle is scraping through previously deposited plastic. What adjustment is needed?

Increase nozzle temperature to improve flow

Slow down the print speed

Increase Z-offset slightly (move nozzle away from bed) — the nozzle is too close

Increase extrusion multiplier for more material

Submit

Explanation: When the nozzle is too close to the bed, excess plastic has nowhere to go and builds up as ridges. The nozzle tip drags through these ridges, creating an uneven surface and potentially dislodging the print. The correct fix is to increase the Z-offset in 0.02-0.05mm increments until the first layer is smooth and flat without ridging.

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Questions 11-12: Mechanical Alignment

How can you verify that a printer's X and Y axes are perpendicular (square)?

Print a circle and check if it looks round

Print a square calibration cube and measure diagonals — equal diagonals confirm squareness

Listen for unusual noises during axis movement

Check that the bed reaches target temperature evenly

Submit

Explanation: A calibration cube with known dimensions (e.g., 20mm x 20mm x 20mm) printed and measured with calipers reveals axis alignment. If the X and Y axes are not perpendicular, the cube will be a parallelogram — the diagonals will be unequal. Equal diagonals (within ±0.1mm) confirm the axes are square. This is a fundamental calibration step after assembly or maintenance.

A student notices their printer's belts feel loose and can be deflected more than 5mm when pressed. What print defects will this cause?

Under-extrusion and filament jams

Warping and bed adhesion failures

Layer shifts, ringing/ghosting artifacts, and dimensional inaccuracy

Nozzle clogs and thermal runaway

Submit

Explanation: Loose belts allow the print head or bed to overshoot during rapid direction changes. This causes layer shifts (sudden horizontal displacement of layers), ringing/ghosting (oscillation artifacts near sharp corners), and dimensional inaccuracy (parts are the wrong size). Belts should be tight enough to produce a low-pitched "twang" when plucked, with no more than 2-3mm deflection under light finger pressure.

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Questions 13-14: Drive Gear and Filament Path

What is the purpose of the drive gear (hobbed gear) in the extruder, and what happens if its tension is set too high?

The drive gear grips and pushes filament; excessive tension grinds the filament, creating dust and causing jams

The drive gear heats the filament; excessive tension melts it prematurely

The drive gear measures filament diameter; excessive tension gives false readings

The drive gear cools the filament; excessive tension causes thermal shock

Submit

Explanation: The drive gear (or hobbed gear) has teeth that grip the filament surface and push it toward the hot end. If the idler tension is too high, the teeth bite too deeply into the filament, grinding it into powder. This powder clogs the filament path and prevents further feeding. The correct tension allows the gear to grip firmly without deforming the filament — you should see light tooth marks but no grinding or dust.

A student hears a clicking sound from the extruder during printing. What are the two most likely causes?

Loose belts and a worn nozzle

Bed temperature too high and print speed too fast

Nozzle clog (back-pressure too high) or drive gear tension too low (filament slipping)

Thermal runaway and a broken thermistor

Submit

Explanation: Extruder clicking indicates the drive motor is skipping steps. This happens when the motor cannot push filament through the nozzle — either because the nozzle is clogged (resistance too high) or because the drive gear cannot grip the filament (tension too low, causing slippage). Diagnosis: if filament shows grinding marks, tension is adequate but nozzle is blocked. If filament is smooth and unmarked, drive gear tension needs to be increased.

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Last Updated: 2026-03-19 Content Review: Q1 2026