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Yes—you can join short lengths of 1.75 mm filament into a continuous strand with a small printed jig, a narrow-bore PTFE tube, and controlled heat. The important part is not simply melting two ends together. The tube confines the softened plastic so the splice stays close to the original filament diameter instead of forming a blob that can jam an extruder, Bowden tube, or runout sensor.
This design, described by Pete Prodoehl in October 2023, is best suited to recovering samples, spool remnants, and short pieces that would otherwise be discarded. It is a DIY filament fuser, not an automatic inline runout system, and every splice should be inspected and tested before it is used in a critical print.
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How the filament splicer works
The jig holds a short section of narrow PTFE tubing while two filament ends are fused inside it. One end is softened with a candle or another controlled heat source, pulled into the tube, and joined to the second piece. As the plastic cools, the tube limits sideways expansion.
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- Turn into Value: SUNLU Filament Connector can fuse the remaining filament on the spool, maximizing the use of each roll of 3D filament and reducing waste
- Creative DIY: Filament connector easily fuses filament of the same material but different colors. Create vibrant, personalized 3D prints yourself
- Fast & Precise Heating: At room temperature, it takes only about 3 minutes to quickly heat up to 185°C, greatly improving efficiency
- Wide Compatibility: Maximum temperature up to 240°C, which is compatible with a variety of 3D printer filament, such as PLA, PETG, ABS, PA/PC
- Easy to Use: One-click operation, select the corresponding temperature according to the type of filament, greatly improving the user experience
The 1.775 mm measurement is the documented design choice, not a universal standard. Filament diameter and tubing dimensions vary, so test the fit while everything is cold. The filament should slide through the tube without excessive force before you apply heat.
What you need
- The two-piece 3D-printed clamp from the Printables model, which includes STL and OpenSCAD files.
- A short length of narrow-bore PTFE tube, approximately 1.775 mm internal diameter and 2.5 mm external diameter.
- Four M3 bolts, at least 14 mm long, and four M3 nuts.
- A vise or other secure way to hold the jig.
- A candle or similar controlled heat source.
- Clean 1.75 mm filament pieces.
The original design can also be adapted for #4-40 hardware if the CAD dimensions are changed. The printed clamp does not generate heat; the original procedure uses an external candle.
Why a narrow tube matters
A filament splice must be both strong and feedable. A joint that merely sticks together can still fail if it is too thick for the extruder entrance, filament sensor, PTFE guide, Bowden tube, or multi-material feeder.
The clamp keeps the narrow tube from flexing while pressure is applied. The tube then acts as a temporary mold: softened plastic can fuse along the joint, but has little room to form a large radial bulge. This is why substituting ordinary 2.0 mm-ID Bowden tubing may produce worse results even though it looks similar.
Safety first
This process uses an open flame and softened plastic. Work in a ventilated area, keep the flame away from spools, paper, solvents, and printed parts, and never leave the heating step unattended. Do not inhale smoke. If the filament catches fire or begins to char, move it away from the flame and extinguish the candle. Secure the jig in a vise rather than holding it close to the flame. Allow the joint and tube to cool before handling.
A temperature-controlled heat source may be preferable, but the original project does not establish validated heat-gun or soldering-iron settings.
Step-by-step: making a splice
1. Prepare the ends
Cut one filament end flat, at approximately 90 degrees. Cut the mating end at approximately 45 degrees. The flat-cut piece is the end that is heated; the angled cut makes insertion easier.
2. Secure the jig
Install the PTFE tube between the printed clamp halves and tighten the M3 hardware enough to hold it rigidly. Do not crush the tube. Secure the jig in a vise or another stable fixture so it cannot move while you handle both filament pieces.
3. Position the heated piece
Feed the flat-cut filament through the tube and pull it until its end is near the central joining area. Keep the filament aligned with the tube rather than forcing it sideways.
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- Maximize Filament Efficiency: Unlock more value from each filament roll by fusing leftover pieces with the SUNLU Filament Connector, ensuring every bit of your 3D filament is utilized to its fullest, reducing waste and saving resources.
- Unleash Vibrant Creativity: Get creative with vibrant, multi-color prints! The filament connector allows you to fuse filaments of the same material but different colors, making custom designs easy and adding a personalized touch to your projects.
- Quick Heating: Enjoy quick and efficient heating with a fast 3-minute warm-up to 185°C, perfect for those who value speed in their 3D printing process. Note: We recommend using a 5V-2A adapter to ensure the Filament Connector powers on correctly
- Compatible with Diverse Materials: With a maximum temperature of 240°C, this connector is highly versatile, compatible with popular filaments such as PLA, PETG, ABS, and PA/PC, so you can explore a wide range of materials confidently.Friendly Tip: The splicer requires manual mode selection for each filament type. It does not switch automatically. Welding must be performed using the same material.
- Effortless One-Click Operation: Designed for convenience, a single-click operation and adjustable temperature settings provide an easy and user-friendly experience, allowing you to focus more on your creativity.
4. Soften the end
Hold the filament over—not directly in—the candle flame. The original instructions suggest starting roughly 100 mm from the flame and moving closer gradually until the end softens. Treat that distance as a cautious starting point, not a universal setting. Different polymers, colors, diameters, and heat sources respond differently.
Heat only until the end becomes soft. Do not let it burn, char, or accumulate a large molten bead.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problems5. Join the pieces
Pull the softened end back into the tube. Quickly insert the 45-degree-cut mating piece and press the two pieces together with moderate force. Keep them aligned and stationary while the plastic cools.
6. Hold and inspect
The project author recommends holding the joint for approximately 30 seconds. Remove the joined filament after it has cooled, inspect it under good lighting, and run the joint between your fingers to detect a ridge or sharp transition.
Apply a light-to-medium tug. If the pieces separate, cut away the failed ends and repeat the process with clean cuts, better alignment, or slightly different heating.
Testing the finished splice
A splice that looks smooth is not automatically suitable for every printer. Before feeding it into a long or unattended print:
- Inspect the joint for a bead, crack, sharp edge, or visible narrowing.
- Perform a light-to-medium tensile pull.
- Pass it through a short piece of the same filament guide or PTFE path used by the printer.
- If possible, feed it manually through the actual extruder path and runout sensor.
- Use it first in a short, non-critical print.
A direct-drive printer with a short, open filament path may tolerate a splice that fails in a long Bowden tube, a tight reverse-Bowden path, or an automatic multi-material system. A splice can also separate during retraction even if it survives a hand tug.
In the original project, the creator reported joining approximately a dozen pieces and obtaining acceptable test prints. That is a maker’s reported result, not a controlled durability test or proof of compatibility with every printer.
Filament compatibility and mixing
This design is documented for 1.75 mm thermoplastic filament. It is not automatically suitable for 2.85 mm or 3 mm filament; that would require different tube dimensions, jig geometry, and heating behavior.
Rank #3
- Maximize Filament Efficiency: Unlock more value from each filament roll by fusing leftover pieces with the SUNLU Filament Connector, ensuring every bit of your 3D filament is utilized to its fullest, reducing waste and saving resources.
- Unleash Vibrant Creativity: Get creative with vibrant, multi-color prints! The filament connector allows you to fuse filaments of the same material but different colors, making custom designs easy and adding a personalized touch to your projects.
- Quick Heating: Enjoy quick and efficient heating with a fast 3-minute warm-up to 185°C, perfect for those who value speed in their 3D printing process. Note: We recommend using a 5V-2A adapter to ensure the Filament Connector powers on correctly
- Compatible with Diverse Materials: With a maximum temperature of 240°C, this connector is highly versatile, compatible with popular filaments such as PLA, PETG, ABS, and PA/PC, so you can explore a wide range of materials confidently.Friendly Tip: The splicer requires manual mode selection for each filament type. It does not switch automatically. Welding must be performed using the same material.
- Effortless One-Click Operation: Designed for convenience, a single-click operation and adjustable temperature settings provide an easy and user-friendly experience, allowing you to focus more on your creativity.
Joining different colors of the same polymer is the least complicated use case. Mixing brands can still change diameter tolerance, melt behavior, surface finish, printing temperature, and joint strength. Joining chemically different materials should be treated as experimental: a joint may appear fused but remain weak or brittle.
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The finished spool should be considered reclaimed, mixed filament—not equivalent to a factory-produced homogeneous spool. Different polymers, additives, moisture levels, and diameters can cause inconsistent extrusion. The original author also noted that mixed colors and brands make one reliable filament profile difficult to establish.
Troubleshooting
The joint has a large bulge
The tube may have too much internal clearance, too much plastic may have been softened, or excessive pressure may have displaced molten material. Verify the tube’s actual bore, use narrow-bore tubing rather than ordinary Bowden tubing, heat only until the end softens, and reduce joining pressure. Confirm that the clamp prevents the tube from flexing.
The splice breaks under a light tug
The ends may not have been hot enough, may not have been held together while cooling, or may be incompatible. Contaminated or damaged ends can also fail. Cut off the joint, make fresh cuts, and retry with short pieces before committing an entire spool.
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The filament will not move through the tube
Do not force it hard enough to kink or snap the filament. Loosen the clamp, separate the printed halves, and remove the PTFE tube from the side. If a spool is attached, slide the tube away from the spool until the filament is free. The problem may be an oversized splice, filament above nominal diameter, an over-tightened clamp, or tubing that is simply too narrow.
The filament burns
Move it farther from the flame and reduce heating time. Burning plastic can produce unpleasant or hazardous fumes, and a charred end should be cut away before trying again.
The printer jams at the splice
The splice may be slightly oversized, the filament path may be restrictive, or the joint may have separated under retraction. Test the complete printer path before a long print, and use a commercial connector or manual filament change for demanding materials if failures continue.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Splicing is only half the workflow
After joining several remnants, you still need to wind the continuous strand onto a spool without crossing or tangling it. This matters especially for Bowden printers and automatic material systems. A loose chain of joined pieces may be technically continuous but still feed poorly if it is not stored under controlled tension.
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Rank #4
- Turn into Value: SUNLU Filament Connector can fuse the remaining filament on the spool, maximizing the use of each roll of 3D filament and reducing waste
- Creative DIY: Filament connector easily fuses filament of the same material but different colors. Create vibrant, personalized 3D prints yourself
- Fast & Precise Heating: At room temperature, it takes only about 3 minutes to quickly heat up to 185°C, greatly improving efficiency
- Wide Compatibility: Maximum temperature up to 240°C, which is compatible with a variety of 3D printer filament, such as PLA, PETG, ABS, PA/PC
- Easy to Use: One-click operation, select the corresponding temperature according to the type of filament, greatly improving the user experience
If winding and storage are the real problem, a spool-management or rewinding solution may be more valuable than a stronger joining jig. The design also does not eliminate all waste: failed attempts, cutting, and unusable ends still produce scrap.
DIY jig versus other options
| Option | Best for | Trade-offs |
|---|---|---|
| Printed narrow-tube jig | Occasional scrap recovery and low-cost experimentation | Requires tuning, an open flame, manual testing, and separate rewinding |
| Manual filament change | Users with a dependable runout sensor who are present during printing | Avoids making a splice but requires supervision and timing |
| Powered filament connector | Frequent users who want more repeatable heating and no candle | Costs more and may still require cleanup and material-specific testing |
| Integrated spooling system | Recycled-filament workflows and users whose main problem is winding | Higher cost, greater complexity, and limited independent testing for some products |
Commercial devices advertise features such as integrated heating, clamping, automatic shutoff, or spool collection. For example, the WISEPRO connector advertises 1.75 mm compatibility, PTC heating, an aluminum melting chamber, and automatic shutoff, although its product page was observed as sold out and those material claims are vendor claims.
The SUNLU FC01 is another branded alternative advertised for 1.75 mm filament and several materials. Current price and availability should be checked directly rather than assumed.
The WIESAG Endless Splicer is aimed at a broader continuous or recycled-filament workflow, while the related Endless ReSpooler addresses winding. The Slunaz FF1r is more automation-oriented, with vendor-described configurable melting settings, spool collection, firmware updates, touchscreen control, and a web interface. These systems make more sense for frequent use than for joining a few scraps each year.
FIXwelder is more relevant to PET-bottle filament and maker recycling setups. Its listed price and availability should be confirmed before purchase.
When the DIY approach makes sense
- You already own a 3D printer and can print the clamp.
- You have many short lengths, samples, or nearly empty spools.
- You want an inexpensive, repairable tool.
- You are comfortable tuning the process for each material.
- You can inspect and test every splice.
Choose manual filament changes when scraps are occasional, your runout sensor is dependable, and you are normally present. Choose a powered or integrated commercial system when operator time, failed prints, open-flame heating, or frequent splicing costs more than the equipment.
Verdict
This is a compelling low-cost project because it addresses the real mechanical problem in filament joining: keeping softened plastic from becoming an oversized obstruction. The narrow PTFE tube and removable printed clamp are more important than simply applying more heat.
For occasional recovery of 1.75 mm scraps, the jig is practical and inexpensive. It is not proven to work with every polymer, printer path, or automatic material system, and it is not a substitute for controlled testing. Inspect each joint, test it through the actual feed path, and treat a spool made from mixed remnants as reclaimed material with multiple possible failure points.
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