J1 Ribbon Cable strain relief fix?

Hi everyone, I just received my J1.
The issue I’m most concerned about is the failures I’ve read about, and seen pictures of, in the FB J1 owner’s group, is the bending and breaking of the ribbon cable.

Many have had to replace the cable. One owner added some extra layers of the old ribbon to act as a strain relief.

I’m surprised I don’t see other mods or fixes for this critical area. I’d like to address it before even powering up for the first time. It’s a tricky little problem to design a 3D printed fix. Anyone working on something for this?

Maybe add some DuckTape? :slight_smile:

For the time being I put some adhesive Teflon tape on the sharp edge at the print heads. @Mechanikus told me the cable itself must not be fixed as it is a balaced system of flexibility and damping.

Maybe as a additional information: I did not see any pictures from damaged ribbion cables yet (no Facebook here) but in general these cables are rather tricky since they are mechanically a lightly dampened mass between two soft springs (springs = cable elasticity, mass = cable mass, dampening = cable dampening). Anything added to the mass or tto increase the cable stiffness need to be carefully checked not to produce any negative side effects such as increased motion and/or bending at some place - for every possible printhead position and speed. That is why some desktop printers that use similar cables have a “do not touch” warning at these cables.

What I found tricky is that you can easily bend the ribbon cables out of place when working at the printer. Then they will either scratch over surfaces thay normally would not touch, or the flexible fixation at the hotend will not work as intended since it uses the cable bending resistance as a “spring” to push the cable against the protruding nose. If that does not work as intended due to a cable being bent out of place, you can easily imagine getting abrasion at places where you would not want abrasion.

Hi Mechanikus,

Thanks for your reply, and all your work on the nozzle replacement designs.
Here are some photos of others who have had their ribbon cables break, leading to all sorts of errors.
Mostly at the print head, and they can fold either forward or backwards. The problem is worst at the extreme diagonal range of XY motion.

Below that is a photo of my solution, which is a thin rectangle of Polyethylene or polypropylene, about 0.75mm thick, cut about 19mm wide, by 25 long. This material can flex easily and not fatigue. It just slips behind the little clips, and a single wrap of electrical tape. This takes the “edge” off when it flexes. I also put a small piece at the rear ribbon cable mount.

Testing by manually moving the axes through the full range of motion demonstrates this should help prevent the issue.

Thanks a lot for the pictures! Yes, these very much look like a fracture of the underlying material of the foil cable from either too high stress or from fatigue. You can see very well that these fractures are not caused by the supposedly sharp edges of the hotend mount on these pictures, the postion of the fracture does not fit to that.
Inside the silver coating that forms a shield, there should be a stiff (sometimes PEI, but today mostly other plastic since PEI is expensive) carrier with the copper or aluminum foil traces that form the “wires” glued/melted/etc. onto them. Search for “FFC cable” to see how that should look on the inside. If that plastic carrier starts to bend at one place (which is usually identical with an internal fracture of that carrier even if the wires are still conductive), you can be sure that this place will fail not too long afterwards. As soon as you can see such a crease, the only way to lengthen that time span is to splint the damaged area in the same way as you did.

There are two possible causes for such a failure: either overbending with a sharp impulse (e.g. the head crash that was mentioned) or simple fatigue which might be caused by a manufacturing causing a minor damage in the cable that then started to grow from the ongoing bending.

If the damage always occurs at the same place, your solution may work indeed. There is a risk however that you will only shift the position of failure outward. Make 100% sure that you will not get any sharper bending radius next to your support in any case. I would go for longer supports and try to sand these down to form a wedge in order to slowly increase the flexibility of the support instead of having a sharp transition between supported and unsupported area.

And it might pay off to glue some stop onto the hotends to keep them from contacting each other. At the endstops, the firmware makes sure that the hotends are always 24mm apart (measured nozzle centre to nozzle centre) - which means there is a gap of some millimeters between them. A spacer added to the hotends that mechanically ensures that this distance will never be smaller would be a good way to protect the cable to be bent overly in case of head crash.

I think that after seeing these pictures this will be the thing I will add to my printer as well as soon as possible.

Apart from that, it would be great if someone who got replacement cables from Snapmaker could measure these (total length, width and thickness of the area where the contacts are, maybe a close-up of front and back side of the contact areas). Then it might be possible to buy these from another supplier instead of having to wait for a delivery from China.

By the way, the maximum bend I could find when checking was in the back left (for the right hotend) or the back right edge (for the left hotend). In these areas, the cable of the other hotend gets in the way - and bends the cable of the hotend that is in motion even sharper than it would be bent if you would move to the edge where the cable is stretched most. This means for me that users that tend to print in these areas might get these problems more often than others. Do you happen to know if there is any indication of this in the Facebook group?

Edit: added material fatigue of a pre-damaged cable as a possible cause.
another edit: added last paragraph

Here’s another picture.

Screenshot 2023-04-23 152431

This one has two breaks, one folding towards the front, against the small “ramp”, center of picture, and even worse, the sharp break on the far right side of the picture, right at the sharp “clip” that holds the ribbon cable. Both these breaks are right next to the hard plastic fixtures on the print head. Basically the cable self-destruct without some strain relief.

And here is how another owner tried to solve it. After getting the whole ribbon cable replaced by snapmaker, they cut a few smaller sections of the old one and used them as strain reliefs.

Yes, I agree. that picture looks different from the others, here the support seems to be the culprit. But I wonder what happened with that cable before - either I failed to find the right position for the cable being pressed against that support edge or it does not happen on my printer, but so far that sharp edge was always free :thinking:

I noticed today one of my printer’s flex cables was scratching on the top X belt every time the print head went back. A closer look revealed a tiny dent at the bottom rim of the cable, exactly in the lower of the two clamps holding it.

This is causing the cable to go upwards slighly from the print head; in turn the cable is hanging lower in the section bending to the back plane.

I do not really like the fragility of this construction and would be happy to learn about a sturdier one.

I am thinking on how this might be solved… does anybody know where to get a thin (my blind guess would be something around 0.1 mm) spring metal sheet in the dimensions of the cable? Then we could try glueing these together (thin double sided tape should do the trick, but it needs to be temperature resistant - 3M type 926 would work for example*) and let the spring metal take the load, thus preventing the FFC cable from getting bent at weak areas…

edit: maybe that thin gauge metal band (german “Fühlerlehrenband” - I do not know the english name though) might be something, it is available in 25mm width and is made of rust-proof spring steel. It would need to be fixed into the cable clamps on both sides however to ensure bending resistance is identical over the whole length.

If I remember correctly, some industrial-grade plotters / large format printers use this to support the print head cables. Anyone who has access to such a device: go and measure :slight_smile:

*: that stuff is rather expensive, I know. There are other ATG tapes available, but be careful to get that is suitable for long term temperatures above 100°C. You would not want to get the wire become loose at some point…

Would it be feasible to get rid of the clamps moulded to the housing and attach some cable guard printed from TPU instead? The thickness of the TPU could vary over the length to generate a sloped resistance.

For the back clamp, I guess this would be possible even if I am quite unsure if this would actually help - and my experience is that TPU tends to stiffen over time and flips back rather slowly then.
For the hotend clamp, you will likely end up getting trouble due to the high friction TPU generates in addition to the above. I think the solution with the thin plastic pieces or the FFC cable parts might be better than TPU. When it comes to long-term flexibility, my experience is however steel is always better than plastic. There is a reason why cars don’t have plastic suspension springs :wink:

1 Like

Snapmaker is out of stock for FFC cable replacement. Does anyone know what cable specific are so I can order replacement from ffc cable company?