High-performance filaments like PET-CF, PPA-CF, and PPA-CF Core unlock incredible possibilities for strong, durable 3D prints. However, working with these advanced materials requires specific handling, especially regarding moisture control. That's why using a dry box during printing is essential.
Despite best practices, we've received reports from users experiencing a particularly frustrating issue: not only does the filament sometimes struggle to feed, but the PTFE guide tube itself gets pulled into the dry box, jamming against the filament spool. This inevitably halts the print.
Why Does the PTFE Tube Get Pulled Into the Dry Box?
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High Friction & Stiffness: PET-CF and PPA-CF are significantly stiffer than materials like PLA or PETG. This rigidity inherently creates much higher friction as the filament travels through the PTFE guide tubes.
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Filament Tangling (A Major Culprit): These stiff filaments can spring energetically when cut free. If the end isn't secured immediately (e.g., with a filament clip), it can easily slip under another strand on the spool when handled or re-wound. This creates a tangle or crossover that drastically increases the pulling force required to feed the filament later. (This is a critical point – even a single loop caught under another can generate enough force to trigger the issue).
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Inadequate Tube Retention: The PTFE tube connection point on many dry boxes is designed for easy tube removal, often using a simple cap or collet. This fitting may not provide enough grip to resist the high pulling forces generated by stiff, tangled, or high-friction filaments, allowing the tube to slide inwards.
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Cardboard Spool Issues: The cardboard spools themselves can sometimes deform slightly, create drag, or not rotate smoothly on the holder, adding resistance to the filament path.
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Hygroscopic Nature: While not a direct cause of the tube pulling in, remember these filaments must be kept dry. Printing moist filament can cause other issues and potentially increase friction due to swelling or brittleness.
The Result: Friction Overcomes Grip, Pulling the Tube In
Solutions and Best Practices
1. Prevent Tangles Above All (The #1 Cause):
When first opening and cutting the filament, maintain positive control to prevent it from springing wildly.
2. Secure the PTFE Tube Connection:
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- Ensure the existing PTFE tube connector/coupler at the dry box exit point is functioning correctly and gripping the tube as firmly as intended.
- Consider Upgrading the Fitting: Replacing the standard cap or collet with a more secure pneumatic fitting (sometimes called a Trachea Connector or push-fit connector) can significantly increase the grip on the PTFE tube, making it much harder for filament friction to pull it inwards.
3. Minimize Internal Tube Length:
Only leave a very short length of the PTFE tube protruding inside the dry box – just enough to guide the filament smoothly off the spool. A longer internal section provides more opportunity for the tube end to get caught on the filament spool if it does get pulled inwards slightly. Reducing this internal length provides more "leeway" before a jam occurs.
4. Ensure Smooth Spool Rotation:
Check that the spool is correctly seated and rotates freely without catching or excessive drag. Ensure no deformed cardboard is impeding movement.
5. Check the Full Filament Path:
Ensure PTFE tubes outside the dry box are free from sharp bends or kinks, which add unnecessary friction.
6. Proper Loading Technique:
Feed the filament smoothly off the spool and into the tube, watching for any initial snags or visible crossovers on the spool surface.