J-head Mk IV-B seperating from PEEK holder

I purchased a PRUSA Mendel V2 kit from makerfarm.com that included a MK IVB
J-head nozzle with Wades accessible extruder. The specs say the nozzle is .35

I am having a problem where the backpressure when printing is forcing the J-Head
to separate from the PTFE liner and then the PEEK holder.
And of course messing up everything with leaks and such.

I have reviewed a number of similar threads on this forum and am wondering if I just
have a bad design or if I damaged the nozzle?

The perimeter prints and the 1st layer starts. Once it got to the second layer
before jamming creating a mess.
If I move my z-stop higher the first layer just does not stick.
According to prontorface my hot end temp is right at 230C

First, there is no set screw I can find on mine so I suspect this is part of the
problem.

The PTFE is beveled on the J-Head end to fit inside.

I have tried just heating the hot end with the PTFE liner and pushing filament (3mm)
through and it just really won't go.

The J-Head did get pushed hard into the glass once when my z-stop slipped.

I am currently cleaning the J-Head in acetone. And will try to assemble
it again later today.

So my questions are:

1. Did I damage the J-head when it was pressed into the glass?

2. Any suggestions for securing the PTFE into the J-Head?

3. I have read that folks have filaments and such they have used to clean
the nozzle. What are they made of and where would I get such a thing?

4. Do I just have one of the questionable implementations discussed here?

5. I have ordered a replacement from Makerfarm.com but is there a better
US source folks can recommend?

Why not go straight to the maker Hotends?

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__________________________________________________________________________
Experimenting in 3D in New Zealand

OK. There is no set screw on top of the J-head? That is a problem.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

Because of the missing set screw and the fact that they are selling the hotends for the same price as Brian is, it makes me think that these are not genuine J-Heads. Brian Reifsnyder from hotends.com is the original and best manufacturer of these hotends. Many of the knock-offs have serious problems.

All:
Thanks for the quick replies. I did later find the set screw - I did not realize it was in the top of the PEEK part - I was looking
for something on the side. Sorry for the confusion.

In any case I am pretty certain I messed up the tip when it pushed into the glass. I cleaned the J-Head in acetone and
was able to force air through the nozzle.

I then set it up on a bench with PTFE in the J-Head , got it up to temp (230C) and tried to manually feed filiment through.
Even with that set up I was not able to extrude any plastic without the PTFE pushing back out of the J-Head.

So I am left to conclude at this point I likely have screwed up the oriface when the nozzle pushed into the glass.
I also think that the threads on the PEEK holder are shot - I suspect it got too hot and with the pressure stripped.

In any case I would have ordered from Hotends.com except he is not producing or shipping right now due to the holidays.
I will check back all week and order a new MK V and a replacement PEEK holder when they are available.

Anyone have any suggestions on how to clean/fix the tip?
I have read where folks have drilled them out with ultafine bits but the cost of the bits would be more than a whole J-Head.

Thanks again for the help and sorry for the newbie mistakes.

I assume your printing ABS by your temps,

Stand it in a jar of acetone (your wife’s nail varnish remover will do)

Let it sit over night and hopefully the ABS will dissolve out and it will become free again, you should be able to see a pin prick of light through it,

Take the PTFE liner out and check your filament pushes through easily, if not then run a drill through it to ease it off (but not to much) 3.2mm drill for 3mm filament and no more than 2mm for 1.75mm filament

I’ve crashed my J-head, even smashed a sheet of glass and never damaged the brass, but i have blocked it up a few times,

If you want a quicker fix Dichloromethane is great, but should only be used under lab conditions (work)

Rob

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Join us at a regular West of England RepRap User Group event
For details, visit tiny.cc/woereprap or tiny.cc/woerug

Rob:
Thanks. Yes ABS. I did the acetone soak and could feel compressed air blowing through the
end. But could not really see any light. The PTFE was fine but with just the head and PTFE I could not seem to manually
push the filament through.

I do suspect I screwed up the threads on the PEEK where the head screws in. I may repeat the whole
Acetone process again and then look to see if I can use a hose clamp or such to hold the PEEK tighter
around the threads until I get a new unit or replacement PEEK.

Hose Clamp!, That quite an achievement, the only way I can get the threads undone on my mk4-b is by putting the Peek in a lathe chuck, setting it to a low gear and getting a big Spanner to the brass bit,

Even with screwed up threads you should be able to see light through the nozzle,

ABS seems to burn after a while and form a hard black substance, it’s a nightmare to get off, especially when in a small hole, you might be able to use a pin or sewing needle to tease a bit out of the ends of the orifice, possibly just enough to get it clear,

The J-Heads are a great nozzle, well made with few leak points but they do seem to need a strip down and rebuild once in a while, I suspect I take mine to work for a clean every 3 months or so

Best of luck
Rob

---

Join us at a regular West of England RepRap User Group event
For details, visit tiny.cc/woereprap or tiny.cc/woerug

Rob:
Thanks.

I should have taken a picture of the brass being pushed out of the PEEK by the back pressure.

I will fool with a pin/needle and see what happens.

New unit has shipped so I should have a new one to try this weekend.

I would suggest you go with the 0.5mm nozzle if your surroundings are particularly dusty. Also, you want to stay away from temperatures that can harm your hot end. I would say, stay at or below 235°C. If you find that you cannot get the filament to melt and continuously at any temperature, it is possible that enough dust has collected in the hot end, and formed a partial of full clog behind the tip.

You can mitigate the problem of dust by keeping your filament covered, and blowing off any dust with compressed air from time to time. There are also some dust trap designs that you can print and build yourself.

Another thing, and a lot of people skip this, is that you need to use heat sink compound inside the resistor mounting hole to get the best heat transfer. This insures that the filament flows evenly at all times, at most printing speeds, without need to go to higher temperatures.

-Wildseyed-

I had the same thing happen to my J-head hot end made from Peek, so I developed my own using Torlon instead of Peek. Torlon has a continuous working temperate of 260° C and I have used them for hours with ABS and they stand up beautifully. You can find them on Ebay. Item number: 150865016722. I am soon coming out with a new nozzle that will be able to be changed while the hot end is still mounted on the printer. filament sizes are Φ3.0mm and Φ1.75mm and nozzle sizes are Φ.35mm, Φ.50mm and Φ.60mm. I devoloped these for my own use, but decided to offer them to the Rep Rap community. Many peaple have them an I have had good rusults with these hot ends. I hope you solve your problem, but if not you might consider the MT2 hot end.

Martyondrums

Nice looking hot end. I wish I had seen this a couple of days ago, before I bought some
more nozzles.

I really like the replaceable nozzle.

I am tempted to purchase one of your torlon bodies if my other nozzles will fit.

Funny, I run JHeads and my own PEEK hot ends at 250C 24/7 for months and the PEEK does not fail. I had one where the brass started to unscrew itself but that was caused by a hole in the PTFE that let plastic flow down the thread. That was after about a year of continuous use and it was still printing fine but the unscrewing caused the Z level to change.

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[www.hydraraptor.blogspot.com]

bytemedwb Wrote:
-------------------------------------------------------
> All:
> Thanks for the quick replies. I did later
> find the set screw - I did not realize it was in
> the top of the PEEK part - I was looking
> for something on the side. Sorry for the
> confusion.
>
> In any case I am pretty certain I messed up the
> tip when it pushed into the glass. I cleaned the
> J-Head in acetone and
> was able to force air through the nozzle.
>
> I then set it up on a bench with PTFE in the
> J-Head , got it up to temp (230C) and tried to
> manually feed filiment through.
> Even with that set up I was not able to extrude
> any plastic without the PTFE pushing back out of
> the J-Head.
>
> So I am left to conclude at this point I likely
> have screwed up the oriface when the nozzle pushed
> into the glass.
> I also think that the threads on the PEEK holder
> are shot - I suspect it got too hot and with the
> pressure stripped.
>
> In any case I would have ordered from Hotends.com
> except he is not producing or shipping right now
> due to the holidays.
> I will check back all week and order a new MK V
> and a replacement PEEK holder when they are
> available.
>
> Anyone have any suggestions on how to clean/fix
> the tip?
> I have read where folks have drilled them out
> with ultafine bits but the cost of the bits would
> be more than a whole J-Head.
>
> Thanks again for the help and sorry for the newbie
> mistakes.

I was going to say, i know makerfarm hotends have the set screw.

But I also have a big problem with backpressure on my makerfarm mkIVb. I think it's in part due to our small nozzle size and the fact that Colin's hotends still have a nipple.

I'd love to know how you make out. I've got a mkVb from Brian R., I'm interested to see if it's better.
I've also had a huge problem with the makerfarm tip catching on my prints.

"The J-Head did get pushed hard into the glass once when my z-stop slipped. ...So I am left to conclude at this point I likely have screwed up the oriface when the nozzle pushed into the glass."

So sorry to hear that you screwed up your j-head by pushing it into the glass when your z-axis slipped. Hopefully you can fix it, but if not, fortunately they're not terribly expensive.

Edited 3 time(s). Last edit at 02/25/2013 09:26PM by xiando.