Anti-Sag：Improved CORE One Extruder Cable Sag Solution, MMU3 Sag fix, With or without MMU, SwingArm support improved, step-by-step guide

Anti-Sag!

The most Reliable and Permanent Solution for CORE One Extruder Cable. With or without MMU3!
Improved, inspired and remixed from Alienbliep's idea, with origin in hachleitner's design.
All 3D models are built from scratch, referencing existing work. 

Clips with PTFE holders are now added, with editable .STEP and .f3d files available. (20 Nov 2025 update)

Key Feature

• Using stainless steel metal-strap for supporting extruder cable. (Easy to source, check below)

• Zero sagging protects your ultra-fragile extruder cable in the best possibly way.

• Improves reliability for long-term use, and create a better “curve”. Enable by independent detachable clip-in fixture installed on the main body of the Nextruder, rather than on the PTFE-fitting in existing designs, with no glue required.

• Budget friendly, East to install, requires only simple materials.

• Support ultra-high chamber temperature, up to 950℃ (melting point of steel).

• Build to last longer than your printer, an heirloom candidate (it's steel!).

• （Optional）If you prefer plastic, still, a plastic version is available without the advantages.

　　　　　　　　　 ▲ Holders with PTFE holder is added to the files. 

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Materials List

Materials

1. Stainless steel cable tie:  ×2-4 pcs, 7.9-8mm width, ≥550mm length
   Mine is 0.25mm thick, but just stack less if you source a thicker one. 
   I source them from local warehouse, see also Ali1/Ali2 (worldwide), Amazon (EU), Mouser (worldwide)
    

2. Printed parts: A×3, B×3, C×1
   Choose A1,B1 if you don't need to fix the PTFE tube, choose A2, B2 if you need to fix the PTFE tube.
   Due to Core One's chamber temp can go up to 65℃ in practice, please use heat-resistant material such as PETG/ABS/ASA/PC/PBT/PA-CF/PPA/PPS… etc.
   I print them using PETG and PC, with 5 walls to make it solid, no problem so far.
   Please note that pure PA is not recommended!
    

3. Screw: M3×6mm ×1
    

4. (optional) Self-adhesive Rubber/Foam: 6cm long ×1
   For soft damping and to prevent noise.
    

5. (optional) If 1. steel cable tie is too hard to source for you, you can also print the strap (file D×1)
   Please only use PC/PC-ABS/PC-PBT, because the support strap is under constant deformation and is holding the cable's weight. ABS/ASA may also work, but not tested yet.
   DO NOT use PA or fiber-reinforced PA, it will bend over time (tested). Also, rigid materials would be too stiff for this use case, other semi-flexible materials seems unable to keep the shape (untested).

Tools

1. Plier (Combination pliers) or steal metal shear

2. Tungsten pen or sharp blade

3. Drill bit Ø 3mm, Ø 1mm (optional for pilot hole)

4. Ruler >50cm

5. Sand paper #60-240, for deburring

6. (optional) A cute cat hanging around (which I sadly don't have)

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Guide for Making

1. Preparation

▼ Print everything and prepare the required materials. 
It will take around 10–30 minutes for the make and installation.

2. Support Strap Making

▶ Cut 2 to 4 steel cable ties to 49-50cm.
Please cut from the fixture end, otherwise you will need to cut twice.

▼ It's best to start by making vertical marks using a tungsten pen.

▼ Then, bend the steel cable ties, and clamp it tightly with pliers.

▼ Bend it backward, and clamp it flat again.

▼ At this point, you should be able to cleanly snap it, by bending it back and forth with pliers.

▼ Slightly sand the end corner, for safety.

▼ Now, turn to the other end, and drill a Ø 3mm hole around 2-3cm away from the end. 
Tungsten pen can be used as center punch, drill a Ø 1mm hole first as pilot hole is suggested.
Steel is hard to drill, apply sufficient force downward. Please make sure to use a sacrificial piece of wood underneath, that would help a lot.

▶ Check the steel strap again, they should be 49-50cm in length, and there should be 2 to 4 of them, normally 2 is enough. 

3. Assembly

▼ Bend all the steel straps one by one around 2.5 turns, this will shape them into a slight curve.

⚠Careful, this may cause harm to your body (especially eyes), do it at your own risk

▼ Install 2–4 straps to the printed part C, and screw the M3 screw to fix them.
Do not overtighten, just make sure it's all the way in, and that would be enough.
It should be unnecessary, but if you prefer using threadlocker (Loctite), please make sure the one you choose is NOT corrosive to plastic, and anaerobic one won't work as well.
Normal high temp superglue like HUH POWER glue would be a much better choice, but glue is optional. 

I personally recommend using 2 straps. 3 also works, but I found it a bit too bouncy in rare cases, and 4 would not be too stiff in my case, I don't think anything more than this is reasonable.

▼ Install all printed part A and B by order. 
The smaller A goes first, followed by B with the extra clip. Mind the orientation!

▼ Slightly bend the other end 1mm with pliers.
Do it strap by strap, 1mm is enough, more will scratch the Prusa SwingArm.
Mind the bending orientation! 
Do NOT bend it the other way; it may hurt your fingers when servicing the machine.
If wrong, detach the straps by unscrewing from printed part C and reinstall the flipped around way.

⚠ Do NOT skip this step.
 

▼ Check if the straps can bend freely, and make sure the printed part won't fall-off.
If done properly, it should look like this.

4. Installation

▶ Firstly, we need to take the top panel off the printer.
▶ Remove the original PTFE_CLIP (only if you have MMU3 installed) from the top of the extruder.
▶ Untie all the black Velcro cable ties, we don't need them anymore, and place the PTFE tube elsewhere.

▼ Install the fixture first, and then clip the cable in one by one for the first three clips.
The fixture is design to be tight-fit, no glue required.
The distances between clips don't really matter; just try to make it a bit even, and that will be sufficient.

▼ For the last three clips, make sure to clip onto the Prusa SwingArm BEFORE clipping the cable, to prevent pulling the cable too much. 
There are three grooves on the swing arm, please clip onto them.

▼ Final check! 
Disable the motors (LCD menu > Control > Disable motors) and move the printhead around, while making sure nothing is in the way and no weird sounds appear.
The strap should not sag; that's the whole point.

The Anti-Sag should NOT make any noticeable resistance when moving around; resistance should only come from the stepper motors.

5. Almost Finished! (optional sound-proof damper)

▼ Fast moving printhead may knock against the back panel.
And it will make a “Clunk” noise when they collide.

▼ Cut the Self-adhesive Rubber/Foam into 4+2cm length.
And cut some grooves on the 4cm one, to make it more flexible.
Only one or two cut in the middle for 2cm one. 

▼ Attach the longer one on the steel support-strap, approx. 1cm away from the SwingArm.
Attach the shorter one on the end of the SwingArm, leaving approx. 1mm overhanging from it.

For making without MMU3 

20 Nov 2025 update: files added!
▶ Follow every step above. Print A2x3, B2x3 and Cx1 
　 (or A1x2 + A2x1 if your PTFE tube is still attached into the print head)
▶ Fix the PTFE tube on the clips as the final step.
 

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You are good to go 😊

☕ Please consider downloading, leaving a like/review, adding this to your Core One collection, and sharing with your friends!

💰 As a student major in Archaeology, I do all these by myself in my spare time, and am self-funded. 
I do not accept donations. If you wish to give something back, please consider using my referral code when purchasing from Prusa: @JamesW_2136542 (enter at the check-out)

Hope you find this helpful!

Happy printing, and may the freedom be with you.

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Change log

• 20251118 rev1 v3
  Created.

• 20251118 rev1.1 v3
  Add optional sound-proof damper, miner fix of the instruction.

• 20251120 rev2 v5
  Redesign with PTFE tube!

• 20251209 rev2 v5
  Adjust the instruction, recommend using only 2 straps.