The Hotend Wire Broke Itself MK3S  

RE: The Hotend Wire Broke Itself MK3S

It got caught on something during your print. This is unusual and there are a few things to check.

1. Are any parts of print bed cable cover sticking up into cables? Check with bed max forward towards you and carriage to left. None of the plastics or bolts should touch your extruder cables. If so switch to newer cable cover or redo cable bunding to keep heater and thermistor secured upward.

More complete solution is to switch to a Bunny Science universal x-carriage which has a protective cable routing scheme 

2. Was a crash into a printed object able to snare the wire and snap it. Good lead dress to keep the wires up reduces this risk

3. Wire fatigue due to excess tension with over enthusiastic zip ties. Don't put the wires under tension as you tighten the zip ties. They need to be supported, not tensioned.

RE: The Hotend Wire Broke Itself MK3S

The screws on the bed stick up pretty far. I'm pretty sure the cable cover caught on one of these causing the cable to snag.

RE: The Hotend Wire Broke Itself MK3S

Prusa has new version of that cover with bolts going DOWN to avoid this.

Great alternative that works well inside LACK case (with limited rear space) is https://www.thingiverse.com/thing:2964580

 I have the front center bolt going DOWN in that cover.

RE: The Hotend Wire Broke Itself MK3S

Okay I have everything working again. I replaced the hotend, and rewired everything.

Now I'm printing the bottom and top from thinguniverse.

One thing I've noticed from the manual.

https://manual.prusa3d.com/Guide/7.+Heatbed++&+PSU+assembly+(Black+PSU)/1153?lang=en

It just seems like these two screws on the build plate could be half as long.

RE: The Hotend Wire Broke Itself MK3S

Those are not screws. Those are locator pins.

Just make sure the extruder cables are correctly supported by the nylon filament.

Nothing should be able to touch the locator pins.

RE: The Hotend Wire Broke Itself MK3S

Each time the calibration runs at the start of the print, the wire cover touches the locator pins. I might add another nylon rod coming out of the electronics box to keep the wires a little more straight so they can stay just out of reach of the pins...

RE: The Hotend Wire Broke Itself MK3S

We need a picture...

My extruder cable, supported by the printed support column, never droops below horizontal.

A picture might show us what is going on.

And it is kind of hard, getting that nylon filament correctly secured. One of my cables flexed so much I was sure the wires would snap - until I fixed it.

RE: The Hotend Wire Broke Itself MK3S

You can see the cables get pretty low. An extra nylon rod in there would lift it up a bit.

RE: The Hotend Wire Broke Itself MK3S

Larger image

RE: The Hotend Wire Broke Itself MK3S

I printed a 20mm X 112mm block and wrapped that into the wire sheath and that keeps things high enough to not brush the locator pins.

RE: The Hotend Wire Broke Itself MK3S

Let me try adding some shots of mine:  

RE: The Hotend Wire Broke Itself MK3S

How low do you get when it's calibrating zones 7, 8, and 9? It looks like you have a nylon rod coming out of your wire box. Your wires are erect where my wires come out limp at a 90 degree angle.

RE: The Hotend Wire Broke Itself MK3S

Sure sounds like you are missing the nylon rod.

Check the construction manual starting at Step 32:

https://manual.prusa3d.com/Guide/8.+Electronics+assembly/1052?lang=en

This rod is critically important to keep the wires from flexing and breaking.

And my cable never gets below horizontal...

RE: The Hotend Wire Broke Itself MK3S

From the Step 32 photo, it didn't explicitly mention it, but it looks like it's twisted 4 or 5 times to keep it rigid?

RE: The Hotend Wire Broke Itself MK3S

That nylon is stiff stuff. I don't think it is wrapped at all.

Hard part is getting enough out to be firmly secured in the hole at the Einsy end.

Like the instructions say - you may need to back off the sheath a bit to get enough out.

The extruder end is really secured by all those zip ties.

RE: The Hotend Wire Broke Itself MK3S

Now that I'm wrapped tight, the drooping slack is gone and there's no concern that it would ever touch the pins. It pretty much is horizontal now.

Thanks for the hint. It looks right now.

RE: The Hotend Wire Broke Itself MK3S

Congratulations - and Happy Printing!

RE: The Hotend Wire Broke Itself MK3S

I just experienced the same issue....does anyone know If you can purchase just the new wire, and not the entire hotend assembly? $80 seems steep to replace a wire 🙄

RE: The Hotend Wire Broke Itself MK3S

Posted by: @gweeen575

I just experienced the same issue....does anyone know If you can purchase just the new wire, and not the entire hotend assembly? $80 seems steep to replace a wire 🙄

If you can get the old thermistor out, that may be all you need to replace. If your hotend parts are bonded together, you could require:

• Heatbreak
• Heater block
• Thermistor
• Heater cartridge
• Nozzle

If you're lucky, it's a $15 thermistor. If you're really unlucky, $65 or more. You really need to take a look to see what can be removed successfully.