Broken PTFE insulator

Hello everyone,

I have a Longboat prusa bought from the reprapkitsore, and so far I still haven't printed anything
I've had several setbacks and the last one is that my PTFE insulator broke.
The thread at the end of the cylinder just broke. I had by extruder clogged, and after a while some plastic started to leak between the brass nozzle and the ptfe insulator.
I unmounted the whole thing and discovered that the thread had died. I managed to unscrew the broken part off the nozzle.

So here I am. I basically just need a new PTFE insulator to be ready to print, and I'm not too keen on buying a whole new hot end cause already had to buy a new set of stepper controlers (another story) and this reprap is starting to cost me quite a lot.
I tried to look on the wiki, on google and on ebay but I didn't manage to find the part I need.

Any idea or suggestion?

Thanks everyone.

Pierre

Well, that design is notorious for having a weak spot where the two materials meet. You CAN make a shorter insulator out of what you've got left, turn down the PTFE until its close to the same OD as the threads and it will self-thread into the brass or steel barrel (I did it with a hand file and six-pack of beer while watching TV), but the problem WILL reoccur eventually. Its at best a short-term solution and probably only for PLA because the extrusion temperatures are lower than for ABS. I think you can order just that part from Mendel-Parts, but he is notorious for very slow service.

I may have a spare or two full-size ones suitable for 3mm filament socked away after I gave up on those and went with the Makergear hot-ends, PM me with a mailing address and if I can find them I will mail you one.

That happened to me twice, even though I followed all the instruction as being NOT STRUCTURAL. I guess it broke because of the pressure built up after some time of printing.

Newer versions now use PTFE tube instead of a block, I'm using it and it is ok so far.

I had exactly the same issue with the same kit. It is a design/reproduction error:-

[forums.reprap.org]

What I did was to drill out the M8 thread in the brass to approx 7.5mm (to just leave the slightest trace of grip) and then turn the end of the broken PTFE to fit really well, and put a step on the end of the PTFE part so that it can slip inside the PEEK part enough for the shoulder to support the brass bit. I then made an aluminium spacer to go above the PTFE to keep the length correct. It now works really well.

I hope this is some help.

George

I decided to go with this design when I first started over a year ago. I had it fail in the same way. I moved on to a brass rod screwed into the PTFE. It also failed either by ejecting the brass rod or ballooning in the middle.

I've since designed a PEEK / PTFE hybrid that works flawlessly. It's the only way to go in my opinion. A hot end that relies on PTFE for any sort of mechanical strength will fail eventually.

Thanks people for your answers.
In a very short term I'll try Mkouri's tip. But from all I can read this problem is going to come back with a PTFE insulator under mechanical contraint.
So next step will be to look at alternative extruders.
If I buy a new whole thing, do you have any recommendation on the nozzle size? 0.5 is standard I understand. What would be the advantages over a 0.35?

Have a good day.

Pierre

If you haven't printed successfully yet, stick with .5mm. You need to get printing before you can start worrying about refining your print quality.

ps same failure mode for me, btw.

aplavins Wrote:
-------------------------------------------------------
> I decided to go with this design when I first
> started over a year ago. I had it fail in the same
> way. I moved on to a brass rod screwed into the
> PTFE. It also failed either by ejecting the brass
> rod or ballooning in the middle.
>
> I've since designed a PEEK / PTFE hybrid that
> works flawlessly. It's the only way to go in my
> opinion. A hot end that relies on PTFE for any
> sort of mechanical strength will fail eventually.


This design isnt really supposed to rely on the PTFE for its mechanical strength. The tensile load from extruding should be taken by the PEEK block and the two M4 screws on each side. But the particular execution of the design that comes with the Longboat from thereprapkitstore is flawed and so the PEEK block cannot support the brass tip properly and the particularly weak end of the PTFE part ends up seeing tensile loads that soon break it. If you simply re-jig the parts so that the PEEK part CAN support the brass tip then it works really well. Since I fixed mine I havent had any problems at all, never cleaned it out or anything and I have gone though most of the 100m roll of PLA.

George

why does the PTFE fail? would the glass mixed stuff work better?
I've found a place here that does different grades/mixes of PTFE and glass, wondering if the glass stuff would work better.

Hi everyone,

Just wanted to share with you my first successful prints (Thank you Mkouri!). You guys helped me to solve quite a few problems so thanks.

Here's a quick montage of my reprap (printing a Hangdrum model if you're curious).
Now it will be time for optimization...

Have a good day.

Pierre

Pierre,
Congratulations! I'm glad to see you're finally successfully creating things!

BTW, in the video it appeared like your Y axis belt is a little loose.

If your feeling adventurous and waiting for another one, do what i did as a quick fix. Remove all the threads from the insulator leaving just a round rod, then simply press fit it into the brass, put a "shelf" of something under the brass's shoulder with two predrilled holes in, one each side of the brass and with some spare studding clamp the shelf to the carriage of your printer. Although this expects you to have alot of stuff lying round, itll mean u can get some prints off now instead of waiting.

Ollie

I've had the same problem with my Longboat Prusa. After printing about a dozen objects with varying degrees of success, the extruder motor started skipping, and when I disassembled the hot end I found that the threaded part of the PTFE insulator had broken off.

I'll contact the RepRapKit Store for a replacement, but I haven't had much luck with previous email to them. Is the part for "Hotend V5" from Mendel Parts the correct one? (This one.)

I'd like to avoid this happening again. Can someone conform my understanding of how it's supposed to work? Presumably if there was no PEEK block, the pressure of the incoming filament would be resisted only by the thread of the PTFE insulator, and the brass nozzle would be forced off. When fitted correctly, the PEEK block holds the nozzle relative to the extruder base plate so that there is no pressure on the PTFE thread. If the PEEK block is fitted the wrong way round the nozzle is either inside the block (and not held, because the hole is too deep) or can be forced into it by the filament pressure (though it's a tight fit on mine). And presumably it's also important not to overtighten the PEEK block or the nozzle will exert force on the PTFE thread in the opposite direction.

Is that right?

(Edited: I said the Longboat Prusa instructions were wrong, but after looking at them again they may just be unclear. I'll add a note to them.)

Edited 1 time(s). Last edit at 05/06/2012 12:45PM by ebcdic.

I'm not really familiar with the longboat Prusa, but yes that's the same part I sent to Pierre and that worked for him. Yes, your understanding of how it's *supposed* to work is correct. When the tension on the PEEK block is correct that hot-end design can last for a long time. I probably pushed 10+ pounds thru mine before I moved to the Makergear hot ends.

I tried Mkouri's suggestion of cutting down the old insulator, using a cordless drill and part of an old "Microplane" grater to turn the PTFE, and to my surprise it works, though I'm not sure how long it will last. The shorter insulator makes assembling the hot end even more tedious, as the screws holding the PEEK block prevent you screwing the heating block on after assembly (obviously some shorter screws would solve this).

Thanks to Mkouri for his help!

Hi Ebcdic,

Did you manage to print complete objects with Mkoiri's advice? For me it worked for a while but i had the impression that any print that lasts for more than 30min would be too stressfull for this insulator. Also after a while the thread broke again.
Hope you got good prints/fun anyway.

Have a good day.
Pierre

> Did you manage to print complete objects with
> Mkoiri's advice? For me it worked for a while but
> i had the impression that any print that lasts for
> more than 30min would be too stressfull for this
> insulator.

I printed this, which took about an hour: [www.thingiverse.com]

I'm hoping that now I have the PEEK block installed correctly there will be much less stress on the insulator.