Hot end blockages

[CrazyIvan]

Well I'm glad you've cleared that up for me, here's me thinking all this time that it was the extruder pushing the filament into the hot end that made the melted filament exit the out of the hole through the nozzle.

I don't know how much sarcasm to read into that. If it's all sarcasm, just ask yourself how come pressurised molten filament that can find its way through the threads of an insufficiently tightened nozzle can't also squeeze its way through the tiny gap between filament and tube wall?

[Bikeracer]

The opening post was about blockages at the end of the PTFE tube, I answered that using experience I gained from having had the same problem and also discussing the reason with Qidi support.

It's a very common problem with hotends that have PTFE tube in contact withthe nozzle.

You seem to want to over complicate the answer, I've never heard of a hot end having a melting chamber, the filament path is a straight hole through the heat break which screws into the heating block where it meets the nozzle, also the heat break is not to solidify the filament, it's to stop it melting in the first place, that's why a fan cools it.

[CrazyIvan]

The opening post was about blockages at the end of the PTFE tube,

Yes. If the heat break is not working effectively, the melt can get back and solidify at the interface or even in the PTFE tube itself.

I answered that using experience I gained from having had the same problem and also discussing the reason with Qidi support.

It's a very common problem with hotends that have PTFE tube in contact withthe nozzle.

I don't know the Qidi specifically, but these are general principles.

You seem to want to over complicate the answer,

Not really, but I'm pretty fed up with simple "answers" lacking technical accuracy (eg on FB!). The process is far more complicated than people seem to realise, and when a complication arises they don't know what to do.

I've never heard of a hot end having a melting chamber,

You probably have a different idea of what a "chamber" is. Call it the melt zone if you like. Take the Ender Mk8 nozzle for example (which is just the one I happen to have a detailed drawing of): the nozzle's filament inlet is 2.0 mm diameter, until it reduces to the nozzle itself. 2.0 mm is substantially larger than 1.75 mm (30% greater volume).

the filament path is a straight hole through the heat break which screws into the heating block where it meets the nozzle,

That depends on the design of the hot-end. Some models use a long nozzle assembly which goes right back through the heat break to the feed tube (especially direct drive hot-ends).

also the heat break is not to solidify the filament, it's to stop it melting in the first place, that's why a fan cools it.

That's where I think you are simplifying too much.

Even melted filament is quite viscous, and although it will just ooze out of the nozzle under gravity, to achieve any kind of printing speed it has to be forced out under considerable pressure. As I said before, that pressure is sufficient to force filament through the threaded fitting of a nozzle if the nozzle isn't screwed in tightly enough, and that usually means tightening it when it's hot.

By the same token, the melt will also easily find its way back between the solid filament and the tube wall. It's only because the heat break solidifies it that it doesn't reach the feed tube, and it's only by becoming solidified that the pressure is maintained to force it through the nozzle.

The effect of the melt backing up and meeting the heat break is to form a seal. The extruder has to be strong enough to continuously force the seal through the heat break into the melt zone, and an equilibrium is established (for any particular set of conditions including feed rate). Therefore, the internal bore of the heat break has to be very smooth, preferably polished,

I don't mind debating this sort of thing, I don't know everything, but please don't be close-minded. I am quite sure the first person to put together an FDM printer didn't realise the complications and took a punt which happened to work.

The thing that have difficulty getting my head around is why it starts out printing well only to fail after printing some 50 or so things what changed.

50 or so things continuously, or over a considerable period of time (with cool-down periods)?

[Philpow49]

50 things is an estimate time period about a year but this is a new assembly and the first print I have a picture (if I could work out how to attach it) showing a clog with plastic extruding up the outside of the PTFE tube.

[CrazyIvan]

50 things is an estimate time period about a year

OK, fairly irrelevant then.

but this is a new assembly and the first print

Explain please. New assembly of what?

I have a picture (if I could work out how to attach it)

See https://www.3dprintersforum.co.uk/viewtopic.php?t=197

showing a clog with plastic extruding up the outside of the PTFE tube.

Ye gods. So the heat break isn't doing its job, and perhaps the nozzle is blocked to make that worse. Do you swap between filament materials?

[Philpow49]

well I'm back I fitted a nice Micro swiss all metal hot end it was doing quite well and then started clogging I shal investigate and find out what I did wrong.

[CrazyIvan]

Any more info to go on? It's difficult to offer suggestions with so little. Is it a nozzle clog or a blockage further up than the nozzle?

A rough guess would be heat creep.

[Bikeracer]

well I'm back I fitted a nice Micro swiss all metal hot end it was doing quite well and then started clogging I shal investigate and find out what I did wrong.

This video might help you...

[bryant]

Hi my printer is constantly unable to print because of blockages these blockages occur between the end of the PTFE tube and the nozzle. Any suggestions please

Make sure your extruder tension isn’t too high — too much pressure can deform the filament at the PTFE-nozzle junction.