J-Head Mk IV-B Issues

So today I was printing an iPhone case for my girlfriend and just to give my printer a good run. While the case was printing, I left my house for about 20 minutes to go get some food. When I came back my J-Head had more or less (in my opinion) exploded. The piece of PTFE tubing lay burnt and twisted on my heated bed amongst a pile of filament. The brass nozzle had cracked from the plastic nozzle holder. The holder is more or less useless now. But to the point of this story, what could have caused this? I've always taken the precautions to keep my extruder and nozzle from getting jammed, so I don't see that as the cause. My next question is, what's a good replacement nozzle to use? I'm not sure if I want to go J-Head again, as I don't trust them much now. It does bear mentioning the I bought it pre-built, but I don't chalk these issues up to that either.

Looking at the print, iether your extruder was extruding too much plastic and/or your z height is not set up correctly. The lumps of p
ASIC that you can see on the service of your print should not be there. I think your J head has caught on them. Normally, this causes the axis to slip or it knocks the item being printed off of the print bed. I think your j head may have been week. If had lots of head strikes as it just happens. I'm guessing we all get them from time to time but I've not come across anyone breaking a J Head before. You can buy the parts from hot ends.com in the US which should be cheaper than buying a whole new head.
Reprap is all about learning. You learn most from your mistakes.
Your first layer has to both be beautifully smooth and well attached. You can only do this if your extruder is calibrated and the head is adjusted to the right height. I do this by calibrating the extruder, levelling the bed so the first layer print is consistent across the whole bed and then adjusting the Z stop to get the smooth but well attached first layer.

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Using ABSPrusa Mendel Zaphod with Pronterface and slic3r 1.3.0. Printing well with 3mm PLA and ABS through 2 x J Head Mk IV b and Wade Geared Exruders. Controlled using RAMPS1.4 board running Marlin_v1.1.9

So do you think that my hot end needs to be higher off of my print bed? My bed is perfectly level to the hot end, so I know it's not that. As for calibrating the extruder, can you link me to a good guide on that? I've followed a few and thought that it was good, but who knows. As for not needing a whole new hot end, I don't feel comfortable using this one at least for the moment. I'm probably going to end up ordering a direct drive extruder, and will get a new hot end with that.

Get your reprap extruder up to temperature. I use Pronterface for controlling mine. Using a ruler or veniers, mark the filament 70mm up from wher it enters the extruder. Get Pronterface to tell your repeat to extrude 50mm. Check, using the measuring device of your choose that the mark has moved exactly 50mm into the extruder. If not, follow

[richrap.blogspot.co.uk]

Having checked that there is no slippage in the extruder.

I then have a gcode file generated with 5 10mm cubes in it, one in each corner and one in the middle of the print bed. I the move the print head in the x direction to its home position and then set the Z axis home switch so that when I home the z axis, I trap a piece of paper between the head and the bed. Adjust the Z home switch until you can ull the piece of paper out. You should feel some resistance. Now move the head to the other extreme on the X axis. Hear you adjust the head clearance by rotating the Z axis threaded rod nearest to the head until you get the same resistance as before when pulling out the piece of paper. Once done, it's roughly levelled and adjusted. Now print the first layer of the test print. On your first layer, the extrusion threads should be consistent across the whole bed. They may be rubbish but they should be consistently rubbish across the whole bed. Don't move the Z home switch yet. Adjust for consistency in the X axis by rotating the Z axis threaded rod furthest from the Z axis home switch. Adjust for consistence in the Y Axis using little bits of paper as shims under the glass print bed.

You should now have a consitent but possibly awfull first layer. Now, very carefully, adjust the Z home switch position until you get a good first layer. A good first layer is where all gaps between the threads are full and the surface is smooth and free of any lumps of plastic. Gaps indicate that the Z home switch is too high. Plastic lumps indicate that the Z home switch is too low.

I print with 0.2mm layers. This probably means that I have to set my Z home position to within 0.05mm. One day I'll modify my printer to allow a vernier control but, with a few tries, I can usually do it as it is.

Good luck with the new print head.

Incidentally, I normally stay and watch the first layer print before leaving the printer unattended as it is so critical.

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Using ABSPrusa Mendel Zaphod with Pronterface and slic3r 1.3.0. Printing well with 3mm PLA and ABS through 2 x J Head Mk IV b and Wade Geared Exruders. Controlled using RAMPS1.4 board running Marlin_v1.1.9

Hello,

I just saw your post and was wondering if you are printing ABS or PLA and what color was the PTFE liner?

The brass nozzle normally doesn't tear out, like that, unless the hot-end is overheated. But, sometimes strange things happen.

Did you get this hot-end at hotends.com?

Regards,

Brian




4t1fy Wrote:
-------------------------------------------------------
> [i.imgur.com]
> So today I was printing an iPhone case for my
> girlfriend and just to give my printer a good run.
> While the case was printing, I left my house for
> about 20 minutes to go get some food. When I came
> back my J-Head had more or less (in my opinion)
> exploded. The piece of PTFE tubing lay burnt and
> twisted on my heated bed amongst a pile of
> filament. The brass nozzle had cracked from the
> plastic nozzle holder. The holder is more or less
> useless now. But to the point of this story, what
> could have caused this? I've always taken the
> precautions to keep my extruder and nozzle from
> getting jammed, so I don't see that as the cause.
> My next question is, what's a good replacement
> nozzle to use? I'm not sure if I want to go J-Head
> again, as I don't trust them much now. It does
> bear mentioning the I bought it pre-built, but I
> don't chalk these issues up to that either.

MotoBarsteward, I'll be trying this when I get a new hot end. I've done something similar with the thumbscrews I installed on my heated bed, but I'll try it your way. Personally I feel that the first layer is too squashed, so that's what I'll be looking to fix.

reifsnyderb, I'm printing neon green protoparadigm ABS with a pre-assembled hot end from MakerFarm. I'm not sure of the original color of the liner, but as you can see, it's white in the picture.

As a point of clarification, I heard a *LOUD* pop noise, which is when I went to see what was happening. I found the two pieces of plastic pictured above hanging out of the end of the hot end where the nozzle had broken off. Maybe it was a jam?

Hello,

The MakerFarm liners are semi-transparent white in color. (Mine are red.)

My guess is that the hot-end died due being slightly overheated and the higher pressure of the Mk IV-B with the nipple on the tip. I have my doubts that there was a jam. However, I would be willing to bet that the temperature was around 248 degrees when the hot-end failed. It doesn't look like a failure where the temperature "ran away" and just kept climbing due to a thermistor failure. But, in my experience, every time the nozzle has been pushed out of the nozzle holder, the high temperature limit was exceeded.

Regards,

Brian





4t1fy Wrote:
-------------------------------------------------------

> reifsnyderb, I'm printing neon green protoparadigm
> ABS with a pre-assembled hot end from MakerFarm.
> I'm not sure of the original color of the liner,
> but as you can see, it's white in the picture.
>
> As a point of clarification, I heard a *LOUD* pop
> noise, which is when I went to see what was
> happening. I found the two pieces of plastic
> pictured above hanging out of the end of the hot
> end where the nozzle had broken off. Maybe it was
> a jam?

I guess I'll just have to watch the temperature next time I fire it up. I've never had the hot end over heat before, but I'll look into it. Is there anywhere in the US where I can buy PTFE tubing without ordering it?

Hello,

PTFE tubing can be obtained either through McMaster-Carr (http://www.mcmaster.com) and I sell the replacement liners (http://www.hotends.com).

At some point, hopefully in the near future, I'll have replacement Mk IV PEEK nozzle holders available as well.

Regards,

Brian


4t1fy Wrote:
-------------------------------------------------------
> I guess I'll just have to watch the temperature
> next time I fire it up. I've never had the hot end
> over heat before, but I'll look into it. Is there
> anywhere in the US where I can buy PTFE tubing
> without ordering it?

I also had problems with my mk-IV from makerfarm until I replaced the nozzle with one from hotends. Now it prints beautifully. Solid layers look as smooth as glass. But before that my mk-IV would just stop printing and sometimes i would see the brass slightly move inside the PEEK holder under a lot of pressure at only 225 C. For me it was the nozzle.

I'm not sure what it was with the MakerFarm nozzle that caused it to pop, but I ended up getting a QU-BD MBE extruder and ended up loving it. If I had to recommend an extruder and nozzle setup, I'd go with that.

I also have a maker farm mkIVb, never blew it open yet but man does that nipple like to catch on everything. I already plan on replacing it. Maker farm should really switch to a mkV...

Definitely have problems with that darn nipple.. same as you it digs not only into my first layer but successive ones as well. Haven't been able to print anything with steep overhangs due to that nipple catching everything...