Markforged Eiger Troubleshooting: Onyx, CFR, Nylon

1. Onyx Warp & Bed Adhesion The Thermal Soak Trap

The reality: Onyx is chopped carbon‑fiber in a nylon 6 base. It shrinks more than pure nylon during cooling. I've seen parts curl up on the smooth PEI sheet, especially large flat areas (panels, brackets). The printer's heated bed goes to 110°C, but the ambient air in the chamber (it's not actively heated) can be 10 20°C below that. That temperature gradient + the material's crystallinity = warpage. Markforged recommends a glue stick (Dimafix or their own). That's a band‑aid if your chamber temperature is uneven.

Step‑by‑Step: Field Fix for Onyx Adhesion

1. Pre‑dry the filament. Even though Onyx is less hygroscopic than pure nylon, it still absorbs moisture. If it's been out of a dry box for more than a day, bake it at 70°C for 6 hours. Moisture causes bubbling and corners lifting.
2. Bed prep not what the manual says. The Markforged smooth sheet works best with a very thin, even coat of glue stick (Dimafix, purple Elmer's). I lay it down as a slurry dissolve a large blob of glue in a spray bottle with distilled water, spray the bed, then wipe smooth with a microfiber. Let it dry completely (10 min at 50°C). This gives a consistent layer without the ridges that a stick leaves.
3. Chamber pre‑heat. I let the printer sit at printing temperature (bed 110°C, nozzle 275°C) for at least 20 minutes before starting the print. This lets the chamber thermal‑soak. If your lab is cold (<15°C), add a foam panel on the top lid to retain heat. Do not block the vents completely the electronics need airflow.
4. First layer parameters. In Eiger, I set the first layer height to 0.2mm (even if target layer height is 0.1mm) and increase the first layer extrusion multiplier to 120%. This squashes the plastic into the glue. Keep the first layer speed at 20 mm/s. I also set the bed temperature to 115°C for the first 10 layers, then drop to 110°C. (Yes, this is above Markforged spec I've done it on three X7s without damaging the heaters.)
5. Brim or no brim? A 2mm brim is fine, but don't rely on it alone. I've seen parts tear the brim off the bed when the warp stress exceeds the glue bond. The thermal soak fix is more reliable.

Troubleshooting Matrix for Onyx Warp

• Part curls at one corner only: Check for a draft near that side (e.g., open door, AC vent). Redirect airflow or add a chamber baffle.
• First layer looks good but fails after 2 hours: The chamber temperature dropped when a new print loaded (Eiger sometimes skips the pre‑heat when printing from SD card). Re‑run the pre‑heat cycle manually.
• Glue stick residue leaves rough bottom surface: Switch to dimafix spray or 3M 77 adhesive (applied to a glass plate, not the PEI). The PEI will wear out eventually you can replace it with a Garolite sheet for better nylon adhesion.
• Onyx stringing on overhangs: Usually moisture. Dry the filament again. If that doesn't fix, lower the extrusion multiplier in Eiger by 5%.

2. Continuous Fiber (CFR) Jams The Abrasion Age

Continuous carbon fiber reinforcement is the Markforged killer feature. It's also the biggest pain point. The fiber is fed through a Bowden tube into the nozzle, which has a larger diameter (1.2mm) than standard nozzles. The fibers are abrasive a few hundred grams of carbon fiber will eat a brass nozzle. When the nozzle wears, the orifice becomes non‑circular, and the fiber doesn't center properly. It catches, jams, and you get a print that stops with half the part finished and fiber sticking out.

Step‑by‑Step: Recovering from a Fiber Jam

1. Stop the print immediately. If the printer keeps trying to feed while the fiber is blocked, you can strip the filament or break the fiber inside the hotend. Hit the emergency stop.
2. Heat the nozzle to 285°C. Markforged recommends 265°C for Onyx + fiber, but I go a bit higher to soften any stuck matrix. Let it soak for 5 minutes.
3. Manually retract the fiber. Use the "Unload Filament" routine in Eiger, but I often have to help it by pulling gently on the fiber spool while the extruder motor is retracting. If the fiber is stuck, you may need to remove the Bowden tube from the extruder and push a 1.5mm drill bit down the tube to clear the path.
4. Inspect and clean the nozzle. Remove the fan shroud and use a brass brush (or a torch tip cleaner) to clear any carbon buildup around the nozzle orifice. If the hole looks oval, replace the nozzle. I keep a spare hardened steel nozzle on hand.
5. Check the Bowden tube. The tube can develop a kink near the hotend where it bends. The fiber rubs the inner wall, producing fuzz. Replace the tube (ID 2mm) if you see any scoring. I've had good results with Capricorn PTFE (low friction).
6. Re‑align the fiber path. When you load new fiber, make sure the spool is perfectly centered above the extruder. Any side load adds friction. I also put a filament guide (a small loop of wire) to keep the fiber straight.

Troubleshooting Matrix for CFR Jams

• Fiber stops mid‑print, no error: Usually a tangled spool. Check the fiber spool I've seen the carbon fiber coil spring off the spool and jam against the holder. Secure the spool with a washer to prevent over‑spinning.
• Clicking sound from extruder: The extruder gear is slipping on the fiber. The fiber diameter can vary (1.75mm ±0.1mm). If it's undersized, the gear can't grip. Calibrate the extruder steps or switch to a metal drive gear (the stock plastic gear wears down).
• Fiber breaks inside the print: Too much tension or a sharp bend angle. Slow down the fiber feed speed in Eiger (I use 50% of default for complex geometries).
• Nozzle oozes fiber during pre‑heat: That's normal but if it strings out badly, the nozzle is dirty. Do a purge cycle before starting the print.

3. Moisture Damage The Silent Print Killer

Nylon is hygroscopic. Onyx is slightly better but still picks up moisture. In humid shops (>50% RH), a spool left out overnight will be wet enough to cause problems. The symptoms: pops, hisses during extrusion, rough surface finish, reduced interlayer adhesion (part strength drops 30-40%), and in bad cases, a jam because the steam expands inside the nozzle and creates a bubble that blocks the filament path.

I've tested this: a fresh spool of Onyx from the vacuum bag prints perfectly. After 12 hours in a 60% RH room, the same print had visible faint lines and stringing. After 72 hours, the part snapped under half the expected load. The manufacturer specs are fine, but the real world is not a dry cabinet.

Step‑by‑Step: Drying & Handling Filament in a Production Shop

1. Don't rely on the vacuum bag. As soon as you open it, the clock starts. I treat every spool as "potentially wet" after 48 hours out of a dry box.
2. Use a filament dryer before every print with nylon-based materials. I use a PrintDry Pro (set to 75°C for nylon, 65°C for Onyx). Bake for at least 6 hours for a full spool, or 2 hours for a partially used one. Crucial: Do not dry above 80°C the spool can warp and cause feeding issues.
3. During printing, keep the spool in a dry box. I built a simple enclosure with a PETG box, a dehumidifier pack (silica gel), and a hygrometer. Feed the filament through a PTFE tube. This keeps the ambient RH under 20%.
4. Monitor printing environment. If your printer is in a basement or coastal area, consider a whole‑room dehumidifier. The chamber of the Markforged is sealed-ish but still breathes.
5. After print, store the spool back in the dryer. If you're not using it for days, or if the humidity is high, keep it in a sealed bag with desiccant.

Troubleshooting Matrix for Moisture‑Related Defects

• Stringing, fine hairs between part features: Most likely moisture. If drying doesn't fix it, reduce the extrusion multiplier (moisture can cause over‑extrusion due to foaming).
• Z‑banding (regular repeating lines): Could be moisture or mechanical but moisture often shows as irregular light and dark bands where bubble density changes. Dry the filament and re‑print.
• Layer cracking or delamination (interlayer failure): This is a classic wet filament symptom. The steam prevents proper fusion. The fix is forced for the next print dry aggressively. If the part is already printed, surface‑treat with acetone (not recommended for structural parts) or consider it scrap.
• Noticeable pop sounds during extrusion: Immediate moisture. Stop the print, unload, dry for 4 hours, reload and restart. Do not try to "power through" it will eventually clog.
• Extruder clicking or grinding on Nylon: Wet nylon becomes sticky and expands in the heatbreak. I've had to disassemble the hotend to clear a fully gunked‑up filament path. Dry your material.

A side note on "dry" vs "optimally dry": I've found that Onyx and Nylon can be over‑dried if left at 80°C for 24+ hours they become brittle and snap easily. Stick to 6 8 hours at 70°C for Nylon, 60°C for Onyx. Use a timer.