The Hotend Wire Broke Itself MK3S  

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timothy.g8
(@timothy-g8)
Eminent Member

Here is a normal hotend with the wires attached.

 

I was starting a new print when the extruder crashed into the left and the UI went non-functional with a ERROR: Mintemp. I couldn't even unload the filament with the UI.

 

I then noticed the thermistor wire was sticking out.

 

I've ordered a replacement. Seeing that the wire broke right on a zip tie, I think I might add a couple more zip ties in there to prevent any kind of repeated bending.

 

I'm not sure exactly how it broke. It's just something that can happen. This is a new hotend from April 2019. Barely even used. So I'm not sure how it wore out...

 

I had just completed a successful 90 minute print.

This topic was modified 2 weeks ago 2 times by timothy.g8
Posted : 05/09/2019 10:14 pm
guy.k2
(@guy-k2)
Noble Member

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.

Posted : 05/09/2019 10:26 pm
timothy.g8
(@timothy-g8)
Eminent Member

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.

Posted : 05/09/2019 10:51 pm
guy.k2
(@guy-k2)
Noble Member

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.

This post was modified 2 weeks ago 2 times by guy.k2
Posted : 05/09/2019 10:54 pm
timothy.g8
(@timothy-g8)
Eminent Member

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.

 

 

This post was modified 1 week ago by timothy.g8
Posted : 14/09/2019 1:55 pm
Robert-mm200
(@robert-rmm200)
Reputable Member

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.

Posted : 14/09/2019 4:32 pm
timothy.g8
(@timothy-g8)
Eminent Member

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...

Posted : 14/09/2019 7:30 pm
Robert-mm200
(@robert-rmm200)
Reputable Member

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.

Posted : 14/09/2019 7:51 pm
timothy.g8
(@timothy-g8)
Eminent Member

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

 

Posted : 14/09/2019 7:58 pm
timothy.g8
(@timothy-g8)
Eminent Member

Larger image

 

 

Posted : 14/09/2019 7:59 pm
timothy.g8
(@timothy-g8)
Eminent Member

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.

Posted : 14/09/2019 8:24 pm
Robert-mm200
(@robert-rmm200)
Reputable Member

Let me try adding some shots of mine:  

 

Posted : 14/09/2019 8:28 pm
timothy.g8
(@timothy-g8)
Eminent Member

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.

This post was modified 1 week ago by timothy.g8
Posted : 14/09/2019 8:41 pm
Robert-mm200
(@robert-rmm200)
Reputable Member

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...

This post was modified 1 week ago by Robert-mm200
Posted : 14/09/2019 8:47 pm
timothy.g8
(@timothy-g8)
Eminent Member

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?

Posted : 14/09/2019 9:00 pm
Robert-mm200
(@robert-rmm200)
Reputable Member

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.

Posted : 14/09/2019 9:38 pm
timothy.g8
(@timothy-g8)
Eminent Member

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.

 

 

 

This post was modified 1 week ago 2 times by timothy.g8
Posted : 15/09/2019 12:21 am
Robert-mm200
(@robert-rmm200)
Reputable Member

Congratulations - and Happy Printing!

 

Posted : 15/09/2019 12:38 am
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