Module 4: Assessment Quiz

Module: U1M4 - Print Execution & Troubleshooting Duration: 25 minutes Passing Score: 70% Format: Multiple choice and scenario-based

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Questions 1-3: Print Monitoring and First Layer Quality

What is the most critical phase to monitor during an FDM print?

The first 2-3 layers, as they establish bed adhesion and dimensional accuracy for the entire print

The last few layers, since that is when most failures occur

The middle layers, because infill problems are most common

Only the support structures need active monitoring

Submit

Explanation: The first 2-3 layers are the foundation of the entire print. Poor first-layer adhesion, incorrect Z-offset, or leveling issues will cause the print to fail — often catastrophically — later in the build. Once a solid first layer is established, many prints can run unattended.

You notice the first layer filament is being pressed very flat and appears translucent. What does this indicate?

The nozzle temperature is too high

The nozzle is too close to the bed (Z-offset too low)

The bed temperature is too high

The print speed is too slow

Submit

Explanation: When the nozzle is too close to the bed, filament is over-compressed, becoming very flat and translucent. This can also cause the nozzle to scrape the bed surface. The Z-offset should be increased (nozzle raised) slightly — typically in 0.02-0.05mm increments — until the first layer shows slight ridges with no gaps between lines.

During a print, you observe that the first layer lines have gaps between them and the filament appears round rather than flat. What is the most likely cause?

Bed temperature is too low

Print speed is too fast

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

The filament diameter is incorrect in slicer settings

Submit

Explanation: When the nozzle is too far from the bed, filament is not adequately compressed against the build surface. Lines appear round and have visible gaps, leading to poor adhesion. The Z-offset should be decreased (nozzle lowered) in small increments. This is distinct from under-extrusion, which would show consistent gaps throughout the print, not just the first layer.

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Questions 4-6: Common Print Defects

What causes "stringing" or "oozing" between separate parts of a print?

Bed temperature too high

Print speed too slow

Insufficient retraction — molten filament leaks from the nozzle during travel moves

Layer height set too thin

Submit

Explanation: Stringing occurs when the extruder moves between separate areas without adequately retracting filament. The molten plastic oozes out during travel, leaving thin strings. Solutions include increasing retraction distance (0.5-2mm for direct drive, 3-6mm for Bowden), increasing retraction speed, enabling "combing" mode, and reducing nozzle temperature by 5-10°C.

A print shows rough, uneven top surfaces with small holes where infill is visible through the top layer. This defect is called:

Warping

Delamination

Pillowing

Ghosting

Submit

Explanation: Pillowing occurs when there are too few top layers to fully bridge over the infill pattern below. The top surface sags into the gaps between infill lines, creating bumps and holes. The fix is to increase the number of top layers (minimum 4-6 at 0.20mm layer height) or increase infill density so the gaps are smaller.

You notice that the corners of a large, flat print are lifting off the bed during printing. What is this defect and what is the primary cause?

Warping — caused by differential thermal contraction as upper layers cool faster than lower layers

Delamination — caused by nozzle temperature being too low

Elephant's foot — caused by bed temperature being too high

Layer shifting — caused by loose belts

Submit

Explanation: Warping occurs because plastic contracts as it cools. Upper layers cool and contract while lower layers are constrained by bed adhesion, creating internal stresses that pull corners upward. Materials with high thermal contraction (ABS, Nylon) are most susceptible. Solutions include using a heated bed, enclosure, brim/raft, and ensuring the room is draft-free.

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Questions 7-9: Troubleshooting Procedures

A print suddenly shifts all layers to one side by approximately 5mm at the same height. All layers above the shift are aligned with each other but offset from layers below. What is the most likely cause?

The STL file is corrupted

Filament diameter is inconsistent

The print head collided with the part or a belt skipped teeth, causing a layer shift

The slicer generated incorrect G-code

Submit

Explanation: Layer shifting is a mechanical issue. It occurs when a stepper motor loses steps — usually because the print head physically hit a curled-up portion of the print, a belt is loose, or the stepper driver is overheating. All subsequent layers print at the new offset because the printer has lost its positional reference. Check belt tension, stepper current, and print speed.

You notice consistent under-extrusion (thin walls, gaps between infill lines) throughout a print. Which of the following should you check FIRST?

Bed leveling

Filament path — check for partial nozzle clog, grinding at the extruder gear, or incorrect filament diameter setting

Print speed

Ambient room temperature

Submit

Explanation: Consistent under-extrusion means less filament is being deposited than expected. The most common causes are: (1) a partial nozzle clog restricting flow, (2) the extruder gear grinding into filament instead of gripping it ("chewing"), (3) filament diameter set to 2.85mm in slicer when using 1.75mm filament. Check the filament path systematically from spool to nozzle.

During a print, you hear a rhythmic clicking or popping sound from the extruder. What does this indicate?

Normal operation sound from the stepper motor

The cooling fan bearing is failing

The extruder gear is slipping or skipping — it cannot push filament through the hotend

The bed heater is cycling

Submit

Explanation: A clicking or popping sound from the extruder means the stepper motor is trying to push filament but encountering too much resistance. The gear skips backward momentarily, creating the click. Common causes: nozzle clog, printing too cold (high viscosity), printing too fast for the hotend's melt capacity, or heat creep causing a jam above the heat break.

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Questions 10-12: Print Management and Best Practices

A 14-hour print is at hour 10 and you notice mild stringing between features but the overall print quality is acceptable. What should you do?

Allow the print to finish and address stringing in post-processing or adjust retraction settings for future prints

Cancel the print immediately and start over with adjusted settings

Pause the print and change the retraction settings mid-print

Increase the fan speed to maximum via the printer's menu

Submit

Explanation: At 70% completion with acceptable overall quality, canceling would waste 10 hours of print time and material. Mild stringing is a cosmetic defect easily removed in post-processing with a heat gun (brief pass at 200°C) or by hand. Document the issue and adjust retraction settings for the next print. Only cancel a print if there is a structural failure or safety concern.

What is the recommended procedure when a print finishes?

Immediately pull the part off the bed while it is still warm

Turn off the printer and leave the part for the next person

Allow the bed to cool to near room temperature, then gently remove the part using a scraper if needed, and inspect for defects

Apply force with pliers to remove the part quickly

Submit

Explanation: Allowing the bed to cool (below 40°C for PLA, below 50°C for PETG) causes the part to naturally release from the build surface due to differential contraction. Forcing removal while hot can damage the part, the build surface, or cause burns. A thin scraper or spatula can assist removal — slide it under the part's edge at a shallow angle.

You are running a long overnight print. Which of the following is NOT a recommended safety practice?

Ensuring the printer is on a stable, non-flammable surface

Using a smoke detector near the printer

Disabling thermal runaway protection to prevent false shutdowns

Having a fire extinguisher accessible nearby

Submit

Explanation: Thermal runaway protection is a critical safety feature that shuts down the heater if the temperature sensor fails or reads abnormally. Disabling it creates a serious fire risk — if the thermistor disconnects, the heater could run at full power indefinitely, reaching temperatures that ignite nearby materials. This protection should NEVER be disabled.

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Questions 13-14: Scenario-Based Problem Solving

You are printing a cylindrical vase (100mm tall, 60mm diameter, 1mm wall thickness) in PLA and notice the walls are wavy and inconsistent starting at about 40mm height. The lower portion looks fine. What is the most likely cause and solution?

The filament is wet — dry it in a filament dryer

The bed is not level — re-level the bed

Insufficient cooling at height — the small layer area doesn't allow enough cooling time, causing deformation. Enable minimum layer time (10-15 seconds) or reduce speed for small layers

The nozzle is worn — replace the nozzle

Submit

Explanation: As the vase narrows or maintains a small circumference, each layer is completed faster than the previous layer can cool. The still-soft filament deforms when the nozzle returns. The "minimum layer time" setting forces the printer to slow down or wait so each layer has at least 10-15 seconds to cool. Some slicers also offer a "lift nozzle" option during wait time.

You printed a mechanical bracket in PETG that needs to snap-fit onto a 25.00mm diameter rod. Your test print measures 24.60mm inner diameter. What should you adjust for the next print?

Increase nozzle temperature to allow more flow

Decrease wall thickness

Compensate for shrinkage and tolerance in the CAD model or slicer — increase the hole diameter by 0.40-0.50mm to account for material shrinkage and achieve the target fit

Change to a different material

Submit

Explanation: FDM prints typically shrink 0.3-0.5% as the plastic cools, and holes tend to print slightly undersized due to the inner perimeter path. For a snap-fit, you need to account for both shrinkage and fit tolerance. Adjusting the CAD model or using the slicer's horizontal expansion/hole compensation setting is the correct approach. PETG shrinks approximately 0.3-0.6% linearly.

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Last Updated: 2026-03-19