J-Head MK5B blocked

Hi

I have a J-Head MK5B (on a Mendel90), which appears to be blocked. I think it has back filled and cooled in the wider, insulated part of the head, meaning it now won't extrude or reverse.

Here's what happened:

1) I started printing a model in PLA with a hot end temp of 220C (as I have already done a few times with the very same filament, and an almost identical model)
2) Unfortunately, for the first time I tried out printing from the PC (actually a Raspberry Pi in my case), but stupidly forgot to run the process as nohup
3) While I wasn't there, the print stopped, when my SSH session ended (stupid of me, I know)
4) I came back to find it stopped - there was a large blob of PLA around the head, and had probably been like that for 15 minutes
5) I set the temp back to 80, enough to peel off the blob on the head cleanly, and reset the printer
6) I then uploaded the model to the SD card, and set it of again. The initial outline (not part of the model, just a line running around the perimeter) looked fine, so I left it unattended again for 40 minutes.
7) When I came back the printer and extruder was moving, but no PLA coming out., and hadn't even got past the first layer.
8) The extruder (Wades gear) was still moving correctly, but no longer moving the filament

I then tried various things to fix:

1) Setting the temp to 220, while manually setting the extruder on, and applying manual pressure at the same time. Didn't budge at all
2) Doing the same, but in reverse - again, didn't move
3) Tried upping to the max PLA temp of 250c, and same thing - would not move either way, even with extruder motor off, and pushing/pulling the filament manually.

I think what happened is right at the beginning of the print, the filament caught an imperfection in the layer, and touched the hotend itself. I expect it then continued pooling around the head, until the outer part solidified, and then back filled. Looking at the blog post here sounds like it might be the case:

[spoolhead.blogspot.co.uk]

So is it possible to fix this? I thought about setting the temp to 250 and leaving it for a good half an hour, hoping the heat would eventually backtrack up and melt the upper part of PLA enough to get the filament going. But not sure if that would burn the PLA, and block the head forever?

So annoying - had printed and almost perfect version of the model, and this was just the last tweak I needed!

Thanks in advance

Marcos

Edited 2 time(s). Last edit at 01/01/2013 04:17PM by marcosscriven.

You can't pull the PLA back out when it is set to 220C? It should pull back out easily even of the hotend is blocked up. Also, are you using a fan to cool the thermal break of the hotend?

---

Help improve the RepRap wiki! Just click "Edit" in the top-right corner of the page and start typing. Anyone can edit the wiki!

If the PLA has backed up into the hotend far enough, you won't manage to melt the PLA that's causing the jam.
IME you'll end up having to pull the PTFE tube out of the hotend, and either replace it or clean it if you can.

NewPerfection Wrote:
-------------------------------------------------------
> You can't pull the PLA back out when it is set to
> 220C? It should pull back out easily even of the
> hotend is blocked up. Also, are you using a fan
> to cool the thermal break of the hotend?

Nope - well and truly stuck! And not using a fan in this particular instance

Polygonhell Wrote:
-------------------------------------------------------
> If the PLA has backed up into the hotend far
> enough, you won't manage to melt the PLA that's
> causing the jam.
> IME you'll end up having to pull the PTFE tube out
> of the hotend, and either replace it or clean it
> if you can.

I guess I'll have to take it apart - it came preassembled as part of a kit though, so not all that sure what I'm doing.

It's pretty much a requirement to use a fan with PLA. Otherwise you will get blockage like you have.

---

Help improve the RepRap wiki! Just click "Edit" in the top-right corner of the page and start typing. Anyone can edit the wiki!

before you go thru all that have you checked with a tiny wire to see if the nozzle is clogged? this happens to me with one particular brand of yellow pla. the pigment is not completely dissolved and it bakes into extruder when it is idle for too long at temp.

jamesdanielv Wrote:
-------------------------------------------------------
> before you go thru all that have you checked with
> a tiny wire to see if the nozzle is clogged? this
> happens to me with one particular brand of yellow
> pla. the pigment is not completely dissolved and
> it bakes into extruder when it is idle for too
> long at temp.

I haven't tried that - but presumably that wouldn't account for the fact the extruder won't reverse either?

Found this thread, looks to be a similar issue: [forums.reprap.org]

NewPerfection Wrote:
-------------------------------------------------------
> It's pretty much a requirement to use a fan with
> PLA. Otherwise you will get blockage like you
> have.


Interesting - I have used the fan, but only for smaller layers and overhangs. Not seen it mentioned using it to prevent this, but will certainly keep it in mind once I get this sorted out.

I have had this one time, and it sounds like filament is clogged in the liner. this comes when having your hotend to hot or a bad line/part of filament.

only way to fix it now is to take apart the extruder and unscrew the top screw in the hotend. Fire it up to 220degree and pull the liner out along with the filament. you will see its clogged there. insert new liner and you are good to go.

This can be prevented by aligning a fan on the top part of the PEEK. struggling with the mendel90 to add a fan to the carriage ive come up with this:
[www.thingiverse.com] this way the heat from the hotend and prevent clogging the liner by overheating the filament.....

I think it may have jammed where the grub screw that holds the liner is. The hex socket in that is bigger than the filament path above and below so if the filament gets soft there it jams.

Unfortunately you can't remove the hot end when it has filament in it without destroying the Wade's block. I changed the design recently to use three screws and washers instead of the integral groove mount.

I have printed plenty of PLA without needing a fan on the hot end but another customer has had this problem when trying to extrude at too low a temperature. The MK5 seems a bit marginal as I have never seen this problem with MK4. Most of the heat at the top is via convection rather than conduction so I got some silicone tape to try insulating the heater but I haven't had chance to try it yet.

I think you will need to break up the Wade's block to get the hot end out and I will need to send you another to the new design. Once the hot end is out if you find the PLA is jammed in the grub screw then the best way to get it out is to heat it with a heat gun until it goes rubbery and then pull it with pliers.

The only other way I can think to get it out is to heat the whole of the hot end to about 70C and then pull it. Perhaps by putting it in a low oven while monitoring the thermistor.

---

[www.hydraraptor.blogspot.com]