My failed Parcan hotend..

I've been using Parcan's hotend for a while and it had been great. I used his version 1 and 2, and there was a huge improvement on his 2nd one already. Anyway, recently, it could not extrude plastic anymore, so I took it out from my extruder assembly, tried to see what was wrong.

I realised that the PTFE tube was slowly being pushed upward as I was pushing the filament down by hand. After pushing though around 10mm of filament, whilst the PTFE tube kept rising, the hotend came to a complete blockage, then no matter how hard I pushed the filament, I couldnt get any through. Also, the top part of the molten plastic was getting cooled and it was so difficult to get it cleared out. I am using PLA and I even had to heat the hotend to 230C in order to use a small narrow piece of metal to force the stuck plastic through the nozzle.

So after I spent 15mins clearing the jammed plastic, I pushed the PTFE tube back in as hard as I could then I repeated the hand extrusion. Again, it worked fine for the first 10-20mm filament, then it became stiffer to melt the plastic, PTFE came up again, then complete blockage again, and I had to repeat the whole cleaning process.

Has anyone had this issue like this? It seems like that the PTFE isnt properly fixed to the brass or PEEK block, so as the molten builds up, the pressure forced the tube upwards instead of coming out from the nozzle.

Can someone suggest what I should do?

Many thanks.
Adrian

Yes I think all hot ends that have thin PTFE tubing will fail like this sooner or later. There is enormous pressure at the join between the brass and the PTFE so it gets compressed upwards. Once there is a gap it jams solid. I haven't used Parcan's but the Wolfgang's suffer from the same problem.

I am coming to think that stainless steel is the only insulator that will last forever.

---

[www.hydraraptor.blogspot.com]

ic... I know the JHead is a popular choice.. but it seems like it also has a PTFE tube inside.. which means it is prone to fail after some time. Also I am a little put off by the length of the support block.. feels like that it will take away a few cms off my Z axis..

has any experienced a failed JHead so far??

Hello,

Unfortunately, there have been a few J-Head hot-end failures that were believed to be due to the PTFE liner. Specifically, if the hollow set-screw is too tight, it can cause the liner to constrict at the joint with the brass nozzle. If this happens, the filament won't properly feed and the hot-end will jam. I would estimate the chances, of this happening, at less than 5%. If this problem doesn't occur, people have reported the hot-end to be working for at least 6 months.

I am planning on fixing both the liner constriction issue and length issue in the next version.

As far as PTFE failing is concerned, PTFE is practically a necessary evil. It is present in most hot-ends, and is required in order to keep the friction to a minimum when printing PLA. Since it is good to 260 degrees Celsius, it will handle the heat quite well as long as it is not used for support in any way.

Regards,

Brian


ahbtsang Wrote:
-------------------------------------------------------
> ic... I know the JHead is a popular choice.. but
> it seems like it also has a PTFE tube inside..
> which means it is prone to fail after some time.
> Also I am a little put off by the length of the
> support block.. feels like that it will take away
> a few cms off my Z axis..
>
> has any experienced a failed JHead so far??

Edited 1 time(s). Last edit at 05/08/2012 09:37PM by reifsnyderb.

The problem is PTFE creeps, so a butt joint doesn't stay tight. It can then be pushed apart by the pressure.

Having said that I have had a J-head running for a few weeks without any problems.

PTFE isn't needed with a stainless steel insulator as long as it has a slight increasing taper, even for PLA. The downside is you need a heatsink and a fan so it isn't so good for moving head.

Edited 1 time(s). Last edit at 05/09/2012 02:47AM by nophead.

---

[www.hydraraptor.blogspot.com]

For my arcol v3 and mp v6, I cut the ptfe tube 1-2mm too long and make sure there's a good support for it on both ends. This way it's compressed slightly and forms a good seal. It seems to require a bit more force to extrude, but I've yet had them fail catastrophically after I did this 6-12 months ago.

I also use a fan to cool down the top of the hot end, and had to beef up the thickness of the extruder base to have it withstand the higher pressure.

---

--
-Nudel
Blog with RepRap Comic

When you say it is compressed slightly that is when it it cold. Under those conditions it forms a tight seal. When heated over time it relaxes and the seal will no longer be tight. That is when the extrusion pressure is enough to force it apart.

I have never known PTFE to keep its shape when hot. I slowly creeps. Thin wall PTFE tubes have lasted for me a minimum of 3 hours and a maximum of about 6 weeks continuous use.

---

[www.hydraraptor.blogspot.com]

thanks for your info guys.

So for my situation now, does it mean my hotend is beyond repair? meaning I need to get a new one??

I think the only part that degrades is the PTFE tube. It gets shorter and the internal diameter therefore gets smaller. If you replace it it should last just as long again.

---

[www.hydraraptor.blogspot.com]

oh. that sounds good. thanks. then I should order some in!

Hello,

Looking over your original e-mail, I'd like to add that to repair the ParCan 2, you will have to remove the brass nozzle from the PEEK and can't just push the PTFE in. The PTFE is held in by being squeezed between the brass and the PEEK. So, once you remove the brass nozzle, you put the PTFE liner over a thin-walled section of brass at the very end of the nozzle and screw the PTFE and brass in together. The PTFE may require a little bit of force in order to get it to expand over the brass.

Regards,

Brian


ahbtsang Wrote:
-------------------------------------------------------
> oh. that sounds good. thanks. then I should order
> some in!

Adrian,

Have you actually contacted Parcan about this. He is keen to know about any issues with his designs as it helps him improve. I think his customer service is great.

I have 2 of his hotends (only using one). I did have a similar figure to yours, but this was after I had been abusing the hot end. I have noticed that when I reflash my firmware, my extruder reverses a bit. With cold filament I think the thicker blob of filament is pulling on the PTFE.

Brian is correct in that you have to screw out the nozzle to fit the PTFE. When you refit it, I found that I had to be quite careful to ensure that I had tightened it the whole way. I took some careful measurements as I didn't want to damage it by overtightening. The first time around I did tighten it enough and it came back out quite quickly.

The design seems to make sense as it attempts to clamp the PTFE, but of course nophead comments stand as no matter how well you clamp it, if it is going to creep when under heated pressure then it will eventually give. I consider the PTFE to be a consumable (although long term, rather than short term).

Hi ahbtsang

I am more than happy to replace your PTFE Tube. Message me and I'll get that in the post.

You can not just push the tube in to the nozzle. The tube is clamped between the Nozzle and the PEEK.

To get you going again, you can use the spare bit of tube you trimmed off to replace the origonal, or you can probably turn the tube over.

Unscrew the Nozzle from the PEEK Insulator. It is tight and is designd to be tight.
Clear out any blockage in the PEEK with a 5mm dia drill.

Put the PTFE Tube onto the Nozzle Top and feed it through the PEEK whilst it's still on the nozzle.
The Nozzle can then be screwed back on to the PEEK until it's tight. 1 - 2 threads still showing.

The PTFE Tube should be held firm by the clamp between the Nozzle and PEEK.

To date I'm still using the 1st MK2 Production nozzle on my own Reprap Menedl. It's not been removed or rebuilt sinse I installed it mid December
That nozzle has printed 6 Prusa and 1 Mendel parts sets and a pile of other items without issue. Probably 10 KG of filament in all.

Alex.

Hi Parcan,

thank you very much for your response.

right at this moment, I am clearing out the jammed plastic in the PEEK block, as the PLA im using is stuck very firmly to it... I was a little bit worried whether I could just drill out the jammed plastic.. but since you've confirmed it, I'm gonna get fixing now.

I'll update everyone how it goes, and very kind of you sending over some PTFE tube for me.

many thanks,
Adrian

To all who read this thread.

I have worked around several open projects over the past 20 years.
I have put together Code, I have made bits and bobs, contributed to forums, IRC and Message boards and I have enjoyed every moment of what I do.

If any one who has purchased one of my products is unhappy with it I am happy to offer a full refund or replacement.
All I ask is that for a refund you return the product to me. If you want a replacement tell me why !

If a product fails in normal use I will be happy to send replacement parts free of charge.
If you crash your nozzle into the bed and snap it off I'm afraid that's your problem......

If you think you can improve on my products or have any other ideas again - I want to know.

My aim is to provide the reprap community with good, well tested and strong robust products that last well.
I think my feedbak here and in other places speaks volumes.

Alex
AKA: ParCan

Hello Parcan

I have one of your hotends (with the peek bar not the peek rod, Mk1 I think) It has been great even though I have abused it.

The only problem I have seen (caused by my abuse) was when I have been cleaning out the nozzle after a nozzle blockage or breakage of thermistor/resistor (yes I have broken them all at least once)

If you are not very careful not to leave any sort of PTFE swarf/dust etc. in the nozzle/PTFE liner (or Bowden tube if you have one that mates with the PTFE liner) the PTFE will not melt at the temperatures used on the printer and so this is a guaranteed failure (I have done this twice now whist drilling out the slightly compressed ends of my Bowden tube assembly and not ensuring that no PTFE swarf/dust is present)

The PTFE seems to crystallise somehow in the nozzle opening, I have used a 0.4mm to successfully drill out the offending PTFE blockage twice so far and all is well.

I have also broken my PTFE liner completely (my abuse again with a drill, ABS is harder than PTFE don’t you know! hey ho you live and learn)

Which had the fortunate side effect for me of allowing me to discover that I can use my PTFE Bowden tube screwed directly into the hotend (PTFE Liner removed completely) simplifying the hotend design if you are using Bowden tubes.

The PTFE Bowden tube I am using is quite thick walled 3mm ID (8mm OD I think) and very stiff but is a perfect fit for this hotend.

and all this begs the question of whether you (Parcan) sell just the brass bits to your hotend, minus the usual extras & PTFE liner at a cost reduction?

Thanks for the great hotend

Graham

Whoops I think I just posted this to the wrong user sorry

Hello Parcan

I have one of your hotends (with the peek bar not the peek rod, Mk1 I think) It has been great even though I have abused it.

The only problem I have seen (caused by my abuse) was when I have been cleaning out the nozzle after a nozzle blockage or breakage of thermistor/resistor (yes I have broken them all at least once)

If you are not very careful not to leave any sort of PTFE swarf/dust etc. in the nozzle/PTFE liner (or Bowden tube if you have one that mates with the PTFE liner) the PTFE will not melt at the temperatures used on the printer and so this is a guaranteed failure (I have done this twice now whist drilling out the slightly compressed ends of my Bowden tube assembly and not ensuring that no PTFE swarf/dust is present)

The PTFE seems to crystallise somehow in the nozzle opening, I have used a 0.4mm to successfully drill out the offending PTFE blockage twice so far and all is well.

I have also broken my PTFE liner completely (my abuse again with a drill, ABS is harder than PTFE don’t you know! hey ho you live and learn)

Which had the fortunate side effect for me of allowing me to discover that I can use my PTFE Bowden tube screwed directly into the hotend (PTFE Liner removed completely) simplifying the hotend design if you are using Bowden tubes.

The PTFE Bowden tube I am using is quite thick walled 3mm ID (8mm OD I think) and very stiff but is a perfect fit for this hotend.

and all this begs the question of whether you (Parcan) sell just the brass bits to your hotend, minus the usual extras & PTFE liner at a cost reduction?

Thanks for the great hotend

Graham