Updated 2026-10-31
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Quick answer: Match the joiner to your filament diameter, join the same material, and follow the maker manual and filament SDS for heat and cool-down. In our planning example, saving 30 g of PLA a month at $0.02 per g is $0.60, so a $25 joiner pays back in about 42 months.
A filament joiner, sometimes called a filament welder, fuses two ends of filament together so short leftover lengths can be joined into one usable strand. Some users join scraps to finish a print, others join two colors for a simple color change, and some just want to stop throwing away the last few metres of every spool. This guide explains when saving scrap is worth it, the main joiner classes, how filament diameter and joint quality matter, the heat tool common practice to follow, and how to work out whether a joiner pays for itself.
Is Scrap Filament Worth Saving
Joining makes the most sense when you regularly have leftover lengths that are too short for a full print. Check your own habits first:
- How much is left on a typical spool end? If you often finish a spool with a few metres left, those ends add up.
- How often do you change spools? Frequent printing means more ends to join.
- What does your filament cost? Saving scrap matters more on higher-priced materials, but joining works best on common materials the joiner maker lists as supported.
- Do you need long single strands? Joined filament can fail at the joint, so many users save joined lengths for small or non-critical prints.
Use our filament cost per print and filament grams to meters pages to put a number on what your leftovers are worth.
Joiner Classes: The Criteria Table
Hobby filament joiners fall into three common classes. Prices are planning assumptions for illustration, not quotes.
| Class | Best for | Watch out for | Planning example |
|---|---|---|---|
| Heated clamp joiners | Repeatable joints with a dedicated tool | Must match filament diameter; hot tip or block | Tool at about $25 |
| Tube and heat kits | Low cost joining using a sleeve and a heat source | Joint quality depends on technique and heat control | Kit at about $10 including 50 tubes |
| Printed alignment jigs | Users who already own a heat tool | Jig must hold ends straight; uses your own heat tool | About 15 g of PLA at $0.02 per g = $0.30 |
Joined filament will never be quite as uniform as a fresh spool, so all three classes need test joints before you rely on them.
Heated Clamp Joiners vs Tube Kits vs Alignment Jigs
Heated clamp joiners hold both filament ends in a channel sized for your filament diameter and heat them together. Once the joint cools, you trim any bulge. They give the most repeatable results for beginners, and some include a built-in temperature setting. Check that the tool lists your filament diameter and materials.
Tube and heat kits use a short heat-shrink or PTFE sleeve to hold the two ends in line while you heat the joint with a separate heat tool, such as a heat gun or lighter-style tool listed in the kit instructions. They are cheap and small, but joint quality depends on how evenly you heat and how long you hold the ends. Expect more practice joints with this class.
Printed alignment jigs are printed blocks or clamps that hold the ends straight while you apply heat with a tool you already own. They are nearly free if you have the right heat tool, but you take on all the temperature control. Treat them as a project, and only use heat tools in the way their maker manual describes.
Diameter, Joint Quality and the Maker Instructions
A joint that bulges or bends can jam in the extruder or hotend, so quality matters more than speed.
- Match diameter. Most hobby printers use 1.75 mm filament, and some use 2.85 mm. A joiner sized for one will not work well with the other.
- Join like with like. Join the same material type where possible. Different materials melt at different temperatures and may not bond.
- Follow the joiner maker instructions for temperature, hold time and cooling time. If the instructions list materials, stay within that list.
- Trim and check the joint. After cooling, trim any bulge and run the joint through a short length of tube or a gauge to check that it passes smoothly.
- Test before relying on it. Pull gently and bend the joint slightly. If it snaps, try again before loading it.
Many users also check joints by feeding them through the extruder on a test print. If you use a filament runout sensor, check that the joint passes it smoothly; see our filament runout sensors guide.
Heat Tool Common Practice: SDS, Cool-Down and Burns
Joining uses heat, so treat it as hot work:
- Read the joiner maker manual for safe use, temperature limits and cool-down times.
- Check the filament SDS from the filament maker for heating and ventilation guidance on that material.
- Work in a ventilated area and avoid breathing fumes from heated plastic.
- Use a heat-resistant surface and keep flammable items away.
- Do not touch the tip, block or joint until it has cooled for the time the manual states.
- Unplug or switch off the tool when finished and let it cool before storing.
- Keep tools away from children and pets.
If a manual gives guidance that differs from this list, follow the manual.
How to Pick a First Joiner
- Want repeatable joints? Start with a heated clamp joiner that matches your filament diameter.
- On a tight budget? A tube and heat kit costs less but needs more practice.
- Already own a suitable heat tool? A printed alignment jig can be enough.
- Check diameter and materials listed by the maker before buying.
- Plan practice joints. Expect several test joints before your first one goes into a print.
- Have a snipper ready. Clean, square cuts make better joints; see our filament cutters and snippers guide.
Worked Example: Calculating Joiner Payback
A beginner prints PLA and finishes about two spools a month. Each spool end leaves about 20 g of filament that is too short to use.
- Scrap per month. 2 spools x 20 g = 40 g.
- Filament value. A 1 kg spool at about $20 is $20 / 1000 = $0.02 per g.
- Value saved per month. 40 g x $0.02 = $0.80.
- Practice and failed joints. Assume 10 g a month lost to test joints: 40 - 10 = 30 g usable, so 30 x $0.02 = $0.60 saved per month.
- Clamp joiner payback. $25 / $0.60 = about 42 months.
- Tube kit payback. $10 / $0.60 = about 17 months.
For this user, a joiner is a slow payback on PLA. It makes more sense for someone who prints more, uses higher-priced filament, or values joining colors and finishing prints over the savings alone.
Storing and Using Joined Filament
Joined lengths are usually short, so a little organisation keeps them useful. Wind joined filament onto an empty spool or a small printed reel, and label it with the material, color and the number of joints. Store it dry, the same way you store full spools, because moisture affects joined lengths just as it affects a fresh spool; see our filament dry boxes guide. Keep the free end secured with a clip so it does not tangle; our filament end clips guide covers simple options. When you load joined filament, choose short or non-critical prints first, and watch the print as each joint passes through the extruder. If a joint catches, pause the print, let the hotend cool as your printer maker manual describes, and remove it before trying again. Over time you will learn which joint settings and materials work reliably on your own printer.
Common Mistakes
- Joining mismatched diameters. The joint will not pass smoothly.
- Joining different materials. They may not bond and can break in the extruder.
- Skipping the trim. A bulge can jam the hotend or catch in the Bowden tube.
- Loading untested joints into long prints. Test first and use joints on short prints.
- Handling hot joints. Wait for the cooling time in the manual.
- Ignoring the SDS. Heating plastic releases fumes; ventilate.
Who This Is Not For
This page is not for recycling filament into new strands, extruder or hotend repair, or multi-material printer upgrades. It is also not for users who rarely print, where the savings are too small to justify a tool.
FAQ
Q: Do filament joiners really work? A: Yes, with practice. Joints work best on the same material and diameter, trimmed and tested before going into a print.
Q: Can I join different filament types? A: It is best to join the same material. Different materials melt at different temperatures and may not bond reliably.
Q: Is a filament joiner worth the money? A: It depends on how much scrap you have. In our planning example, saving 30 g of PLA a month at $0.02 per g pays back a $25 joiner in about 42 months.
Q: Will a joined filament jam my printer? A: It can if the joint bulges or is weak. Trim the joint, check it passes a tube smoothly and test on a short print first.
Q: Do I need a heat gun for a tube kit? A: Tube kits need a separate heat source listed in the kit instructions. Follow the kit and heat tool maker manuals for safe use.
Q: What safety steps should I follow when joining filament? A: Read the joiner manual and filament SDS, work in a ventilated area, use a heat-resistant surface, and let the tool and joint cool before touching them.
Estimate how much scrap you have each month, match the joiner to your filament diameter, read the maker manual and SDS, then practice on scrap before joining for a print.
Related guides
Questions about this guide? Email hello@charlandandco.com.