Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?
 
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Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?  

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J
 J
(@j)
Eminent Member
Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

We've got three Prusas where I work: Two MK3s and one that's either a MK3S or a MK3S+. I'd say they get moderate/heavy use. They are all factory-assembled.
I also have a MK3 at home, built from a kit. It gets fairly light use.

Internal wire breaks from cable fatigue have plagued these printers. It's a continuous-flex application, and the wires used just can't handle it.

-- I've seen a few other posts about this problem here, but I was wondering if anyone knows of any third-party continuous-flex-cable refit kit for mitigating this?
Right now all I can do is keep splicing or replacing wires as they break. Some can be bypassed or ignored temporarily, like an RPM-monitoring wire, but a broken thermistor wire means no printing until it's fixed.

Within the first year or so of operation, I've had these wire-breaks across any of the three printers:
- Print blower fan: RPM wire on one printer, and power wire on another.
- Print bed thermistor (two breaks were found in one wire).
- Print head thermistor.
- Filament sensor.
- Possibly one of the extruder motor's wires, but that printer's thermistor wire broke before I could be sure.

Wire breaks happened with the spiral-wrap wire loom as well as the textile-wrap style.
The breaks weren't all at stress points where the cable ends attach to the printer. Some happened near the middle of the cable bundle.

Even my lightly-used MK3 has had wire breaks in its filament sensor and print blower fan.

I'm attempting a wire-splicing using multi-conductor cable that's rated for continuous flex, but everything in the printer design is so tightly compacted that it might not even work: There's just no room anywhere for the sizable bundle of wire and splices, while still allowing the print head to reach is normal working volume.
The only other thought I've had is some kind of breakout board that would attach to the back of the print head somehow, and another breakout board at the controller: Plug all the connectors from the print head into the breakout board, and then connect a continuous-flex cable between them. Has anyone made anything like that already?

Or I might be looking for a different printer brand, something that at least uses wires rated for continuous flexing. Intermittent problems can damage or completely ruin long print jobs, which is unplanned downtime I don't need; same with replacing broken wires and cables.
I like these printers just fine otherwise, they're good workhorses, but the breaking wires is a persistent problem.

Napsal : 21/01/2022 6:09 pm
Thrill Science se líbí
Zoltan
(@zoltan)
Member Moderator
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

Did you try to contact technical support and discuss with them the issue? 

even an old man can learn new things 🙂
Standard I3 mk3s, MMU2S, Prusa Enclosure, Fusion 360, PrusaSlicer, Windows 10
PRUSA MINI+ Prusalink + Prusa Connect

Napsal : 21/01/2022 6:58 pm
J
 J
(@j)
Eminent Member
Topic starter answered:
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

I did back when some of the wires originally broke. I was sent a new blower fan and a new filament sensor cable. They have since had internal breaks as well from the constant flexing.

I don't know where to take things though when there's an issue with the design itself, especially if it only affects a small portion of their customer base.

Napsal : 21/01/2022 7:58 pm
Diem
 Diem
(@diem)
Illustrious Member

Prusa themselves make very heavy use of their printer farm so they must have considerable experience in this area...

Contact chat and explain the issue.

Cheerio,

Napsal : 22/01/2022 1:38 am
J
 J
(@j)
Eminent Member
Topic starter answered:
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

Update on this old thread:

Back in early 2022, I spliced all the wires on a MK3 to a length of continuous-flex cable from Igus. CF130-05-25-UL for the extruder head, and CF130-05-07-UL for the heatbed. The hotend uses a total of four conductors in the cable, and the heatbed got two conductors for positive and three for GND since there was an extra available. It has been running fine ever since. Zero wire-break issues.

I recently did the "Igus upgrade" to a second printer, and also upgraded it to a MK3S+. Its print blower's wire conductors had finally broken badly enough that it was useless across 100% of the bed, so I finally took the time to deal with it properly.

The newest printer I'm running, a fully-assembled MK3S+, had started developing wire breaks in both its filament sensor and print fan wires in less than 6 months of use, causing intermittent disconnections depending on the location of the extruder head. I had to disable the fan-check and filament sensor monitoring to keep it running; it's next on the list for the Igus upgrade.

I truly don't know how Prusa Research run their print farm 24/7 without constant wire breaks. The regular wires just aren't meant for constant flexing.

 

 

 

Napsal : 09/05/2023 8:03 pm
Thrill Science se líbí
Diem
 Diem
(@diem)
Illustrious Member

What is the average temperature of your workshop?

Cheerio,

Napsal : 10/05/2023 9:45 am
J
 J
(@j)
Eminent Member
Topic starter answered:
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

Three of the printers are kept at pretty standard room-temperature range, about 68-73F / 20-23C.

The newest one is in a large, simple enclosure of 1/4" polycarbonate panels, so it tends to be warmer in there when it's running.

Napsal : 10/05/2023 12:26 pm
Stefan
(@stefan-3)
Estimable Member
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

I truly don't know how Prusa Research run their print farm 24/7 without constant wire breaks.

Possible differences in your usage vs Prusa Printfarm usage:

  • Maybe you fill the entire build plate, while Prusa maybe fills only the center area of the plate. Therefore range of movement is greater in your case.
  • Maybe your parts are higher in Z-direction. Prusa parts have no great Z-dimension. 

Anyway, moving wires in the printer should last nearly forever - no matter how many parts are on the print sheet -  in my opinion.

Broken wires are also  a security risk.

Thanks for pointing to these special IGUS chainflex cables!

 

 

Napsal : 10/05/2023 12:48 pm
J
 J
(@j)
Eminent Member
Topic starter answered:
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

Printing: I do tend to use a fair amount of the total build volume, yes.

My experience with wires and constant-flex applications, and what I've seen in industrial equipment: If the wires aren't rated for continuous flexing, wire conductors can be prone to breakage, possibly unless it's an extremely wide bend radius versus the wire diameter. Continuous-flex cable is typically rated for millions of bending cycles, and has some construction differences from regular wire. For example, in the Igus cable I used:
- Finer stranding than conventional wire, in the range of 2-3x as many strands for the same conductor cross-section.
- Groups of wires are arranged in circular bundles with a string of multi-strand low-friction plastic in the center.
- Those bundles of wires are then arranged around a central string of more low-friction plastic.
- There's a fine, low-friction powder throughout the cable to further helps things slide past one another easily.

The wires on the fans and filament sensor and everything else are just standard-use wires. Constant flexing can lead to internal breakage of the conductors, and the smaller wires on these printers don't have very many strands.

I'll need to upload some printable files sometime, if anyone else wants to attempt the splice-job I did:

- I revised (somewhat hastily) the design of the plastic cable holder that sticks out from the back of the X-axis assembly, to better help hold the cable and the mass of splices and zip-ties.

- Because the splices+zipties mass is kind of large, and the printer has little clearance to spare, I had to put the mass on one side of the plastic cable holder, which caused it to bump into the power supply. So I made a power supply mounter to put the power supply out of the way. Depending on how much slack is in the wires, it may then be necessary to extend the 24V power wires.

- Revised plastic parts for where the cable goes into the heatbed. A nice bonus: If they're printed out of translucent material, like plain PETG, the LED lights up the entire plastic part. 🙂

 

 

 

Napsal : 10/05/2023 2:01 pm
Thrill Science
(@thrill-science)
Member
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

I just had my first "major" failure on my Prusa i3. The wires to the bed thermistor had been dragging along the frame below the bed and eventually flexed too much and failed. I cut out the kinked, frayed part of wire and replaced that segment with a slightly thicker silicon-insulated wire, and taped the wire to the bottom of the bed with Kapton tape. 

 

Having the design where the wire droops below the moving bed and rubs on the stationary frame below is just poor design. Also they should used 1 or 2 gauge wire with silicone insulation.

I might replace the whole run with silicone insulated wire but I just needed to get it working again.

Napsal : 25/05/2023 3:10 am
JoanTabb
(@joantabb)
Veteran Member Moderator
RE:

I use flexible silicone insulated wire for these wires, and I add a Nylon support filament into the bundle too, 
I either use a sample of 3mm nylon filament or weed whacker filament...  (Round stuff, no sharp edges)

4mm PTFE Tube also makes a useful support filament, but the support filament MUST run the full length of  the wire bundle from the heatbed clamp to the einsy clamp, or it will concentrate fatigue where it ends.

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Napsal : 25/05/2023 6:29 am
Thrill Science
(@thrill-science)
Member
RE:

I suppose I should do that, too! Everyone claims the cable inside the bundle will actually break! I didn't even open the cable to examine it. 

On my printer, there were several inches of wire between the grommet at the end of the bundle on the bed and the thermistor that were just dragging along the bottom of the frame. After a couple years of being rubbed back and forth thre wire rubbed bare and failed. Since I don't see other people complaining about this, I presume this was just a "manufacturing defect" (I got a pre-assembled one) and most assemblies don't have a wire that can drag there.

My patch worked well, but I have a new thermistor coming from Prusa. When it arrives, I'll replace the whole thing, and use silicon insulated wire through the wrapped bundle into the control module to make sure it won't happen again.

I've heard that there's a similar failure on the hotend thermistor and the hotend fan with the wire eventually breaking inside the bundle.

This post was modified před 10 months by Thrill Science
Napsal : 25/05/2023 7:28 pm
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: Broken wires due to cable fatigue: Is there any long-term solution, like a refit kit, for dealing with this?

the conductors typically break, inside the insulation sheath, inside the braided cover, to discover the break, you typically need to remove the braided cover, then tension the wire to indicate where the break is. inside the insulation. 

when reassembling, ensure that no wires are pinched, or put under tension, during assembly and that the braiding and suspension filaments are located inside the clamps  at both ends. 
then ensure that the wire bundle is not touching the frame, or the wall!

Best wishes, 
Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Napsal : 25/05/2023 9:57 pm
Thrill Science se líbí
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