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

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? 

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.

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,

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.

What is the average temperature of your workshop?

Cheerio,

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.

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!

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. 🙂

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.

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

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.

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