HotEnd Blowout

So I managed to blow out my Hotend when printing the first layers, When you look at the build plate it printed the top right first, then bottom right, and then bottom left. I have a few questions below:

1) Is this fixable? (I am guessing it isn't but correct me if I am wrong)
2) What could have been the cause? (The fan did bump the bull clip when printing the perimeter but I don't know if that would have caused the blowout)
3) Where is the best place to buy a new MKV J Head hotend?

Cheers,

The pics are not that clear, but it looks like the threads were also ripped out?
Without a clearer picture, its hard to tell.

My first guess is a temp issue. It was too cold, and caused too much back pressure
in the extruder causing everything to blowout...
What were your temps at the time of the blowout?

Hotends is a great source!

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Custom all metal CoreXY
- Duet 2 Wifi w/ PanelDue 7i
- 330mm x 360mm x 500mm
- 750w Silicon heater

Custom Mendel90
(Backup printer - Old reliable!) - Sold

I think the threads were ripped out but they are coverd in PLA. I was printing at 220C with the green PLA that came with the kit.

Looking at Pic #1 again... it looks like there is some blackening around the top of the heating element.
Have you verified your temps? Maybe it was too hot and burnt (and melted) everything?

Can you give some more details about your setup?

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--------------------------------------------------------
Custom all metal CoreXY
- Duet 2 Wifi w/ PanelDue 7i
- 330mm x 360mm x 500mm
- 750w Silicon heater

Custom Mendel90
(Backup printer - Old reliable!) - Sold

Setup was Nopheads kit with everything the standard settings including the PLA that came with the kit and the Skeinforge settings that came with the kit. I had printed for about 16 hours with the setup with no previous problems.

The only thing different from this print is I used the Plater.exe to generate a stl plate.

Thanks.

The few instances of that happening were due to using gcode sliced with absolute E codes instead of relative.

What is platter.exe?

Did you slice it with Skeinforge or something else?

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> The few instances of that happening were due to
> using gcode sliced with absolute E codes instead
> of relative.
>
> What is platter.exe?
>
> Did you slice it with Skeinforge or something
> else?

Out of interest, what is the benefit of having the firmware set to use relative extrusion. Would not using absolute mean that there was no risk to damaging the hot end. i.e. If you made the mistake of saying relative when the firmware expects absolute no harm would be done other than a duff print.

The only reason it can blow out the hot end is because Brian had a tolerance problem making the threads on the J-Heads, see [forums.reprap.org]. Normally the hobbed bolt would slip or the motor stall before it damages the hot end. I didn't foresee that when I decided to use relative.

In general relative causes less problems if you want to, for example, change filament during a print. You can pause and then manually rewind and extrude before resuming where the print left off. Also absolute isn't immune to big jumps if for example the counter gets reset for some reason.

Reprap using absolute E and having the origin in the corner of the bed is one of the many things I think are wrong, so I don't follow suit like a sheep and strive to do things better.

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[www.hydraraptor.blogspot.com]

Plater.exe is a program that combines STLs into a plate, it is in the same folder as Pronterface and came on the microsd with the kit.The SpherePlate.stl (Attached) was the file that I used to slice in Skeinforge. SpherePlate.stl was created using Plater.exe from the two ImpossibleSphere STL (Attached)

I have attached the first ~20% of Gcode (I deleted the other 80% as the file was too big to upload here).

I believe I used relative E values but not 100% sure as I am fairly new to 3D printing. There is a portion of the GCODE below which has a negative sign infront of the extruder command which I would think confirms it is using relative values.

G1 X-20.653 Y-48.022 Z0.3 F1500.0 E0.436
G1 F1200.0
G1 E-0.2895

Reading the thread from Brian would that possibly mean I can get a free hotend to replace my other one? Since you ordered it from Brian, Nophead would I need to get the HotEnd from you or should I email Brian?

Cheers,

Ryan,
Yes it looks like relative E and the bits that it did manage to print look like they have the correct amount of plastic. I will send you another.

In the meantime you might be able to clean it and put it back together. If you have any form of heat gun, or perhaps use hot water, you can heat the PLA to about 60. It becomes like rubber and can by picked out with needle nose pliers.

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[www.hydraraptor.blogspot.com]

I appreciate you sending a new Hotend.

I think the brass part is usable and I will try to clean it but I would need a new black part as the threads were stripped out when the brass part poped off.

Are you sure? I managed to put one together again that had been blown out by absolute extrusion.

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[www.hydraraptor.blogspot.com]

I will clean out both and see if they can be put back together. Is the white tape for the threads just standard plumbers thread seal tape(PTFE)? Or is it something else?

Yes it's PTFE tape as used for plumbing.

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[www.hydraraptor.blogspot.com]

For my own understanding of hotend failures, is it a correct statement to say a hotend shouldn't fail unless there are manufacturing defects, or from fatigue over prolonged usage.

Is it also correct to state the following wouldn't cause a hotend failure:
- For situations where excess plastic was being pushed into the hotend (mis-calibration, ie 3mm filament was entered at 2.75mm filament) there would be lumps of plastic in the print.
- For a blocked nozzle (foreign object or extruder at a cold temperature) the hobbled bolt would slip or motor would stall.
- If the hotend was touching the bed during the first layer the hobbled bolt would slip or motor would stall or there would be plastic lumps.

Thanks.

Yes it shouldn't be possible to push the end out assuming the temperature is not so high that the PEEK melts.

I have never had that happen to a PEEK hot end with any of the conditions you list. It happens all the time with PTFE though.

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[www.hydraraptor.blogspot.com]

I also had a blow out like that happen with a dibond kit from nophead. Not entirely sure what caused it.. but it was not because of absolute extrusion. I had noticed some problem with the first layer so I decided to try to get the z home position properly calibrated.. but no matter what I did the first layer just never got better.. no wonder because the brass bit kept slowly moving downwards everytime I did a test print! So after multiple tries the brass bit finally fell off.

So I just removed the hotend from the rest of the extruder.. held the brass part with pliers while hot.. grabbed a piece of cloth and wiped off most of the PLA from the threads.. and then just screwed it back in while still hot. I definitely could have cleaned the threads alot better.. but the hotend has worked just fine afterwards.. After a couple of weeks I did replace it with another one.. but I kept that old one as a spare as it still works.

I'm thinking that it may have been caused by too high temperatures..Before the hotend failed I had been using temperatures similar to those mentioned in the manual.. and if I remember correctly I was using 220C when the hotend failed..and had previously tried 230C briefly. A temperature like that shouldn't be a problem.. but after that incident I started testing different temperatures and realised that with my printer a good temperature range for PLA is 180-190.. which is way below the values mentioned in the manual. I use 190C for arctic white.. manual suggests 240C!

To rule out the possibility that my hotend was giving too low readings (and because I wanted a smaller nozzle) I ordered a new J-Head.. which uses a different thermistor and also a different thermistor table.. but that didn't make any difference at all. I can still print everything using 180-190C range.

This temperature thing is really weird. I use 1% thermistors and whenever I make myself a new extruder I check the temperature with a thermocouple and it agrees within a degree or two.

220C works fine for the green PLA in the kit for most of my customers but the odd person says 180C. Same plastic, same thermistors, same firmware.

I use 250C for ABS and never had a blow out.

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[www.hydraraptor.blogspot.com]