Clogged nozzle?

This may be really obvious to people who know what they're doing.

After several prints with moderate success, the nozzle started dragging up the raft it was building (temperature too low?). I stopped the print, but now I get no filament out at all. There's no obvious protruding filament; I've taken the nozzle up to 235°C and tried to extrude hoping that the blockage would melt, but the hobbed insert slips. Is it sensible to try to clear the nozzle with a fine needle, or is there something else I should be doing?

There is a procedure for the Ormerod, which tells to cool the hotend to 100°C (use the regulation to have the temperature stabilised), then pull the filament and all the plastic in the extruder will came.
That works, but they forgot to mention something important: you shall do that directly in the hotend, because what is get from the hotend is too big to go through the bowden, so you may reinsert later the cause of your clog. So, first unscrew the bowden tube.
In fact, 100°C is just the temperature where the PLA have sufficient strength to pull the whole stuff, and is sufficiently soft to get the stuff out. If it succeded, you will see the internal shape of the hotend. [`edit] The filament is thinned a lot while pulling it and may break without getting the stuff out.
They suggest to do that at least five time and then to disassemble the hotend, however, what to do after disassembly is not disclosed. I think you shall avoid any use of metallic part for cleaning. The hotend is full stainless steel, so relatively strong but that may not be a good idea. If the above procedure does not succeed, wait RRP instructions !

When you rescrew the bowden, do not overtight (personnaly, I unscrew 1/2 turn after, because I got problems of excessive friction at the end of bowden). There is no risk of leak because at the PTFE junction, filament is not melted.

Edited 1 time(s). Last edit at 07/27/2015 01:59PM by PRZ.

Thanks. I did get a fairly pointy end with a bit of thready filament on the tip when I took it apart, but that didn't help clear it. Nor did gently heating the nozzle with a small blowtorch. My wife eventually managed to dislodge what seems to have been a plug of PLA, using 0.4mm beading wire, and I'll put everything back together later and hope for the best.

Once the 0.4mm nozzle is on the storefront I'll order a spare…

If you succeded to get out the hotend content, it is not really "pointy". Unfortunately, I forgot to make photos of what I get, but you see clearly that you get it out.
What you shall get is a cylinder 2mm diameter with at the end a smaller diameter cylinder with a low angle conical end and the 0.4mm cylinder of the nozzle. In fact it is the shape of the hotend. The 'pointy' part is only the part which pull the end. If you get the pointy part only, it broke before getting the stuff. But as it is 2mm diameter, it wont go through the bowden.

Edited 2 time(s). Last edit at 07/27/2015 02:55PM by PRZ.

Quote
PRZ
If you succeded to get out the hotend content, it is not really "pointy". Unfortunately, I forgot to make photos of what I get, but you see clearly that you get it out.

Just happened to have an extracted piece of filament laying on the bench. Not sure if its from Fisher or Ormerod.

That's it! For the Fisher, from memory, it was slightly different, with two different diameters. Maybe a bit bigger, but scale is quite difficult to evaluate on your photo.

Edited 2 time(s). Last edit at 07/27/2015 03:40PM by PRZ.

Eh well. The clearance didn't work; the filament doesn't want to move more than a few mm forward or backward, whatever temperature I set. Thanks for your help, but I fear it's tech support time.

Hi RogerBW

This sounds like a fairly standard nozzle blockage, but there are a number of reasons why a blockage, or a failure of the extruder to drive the filament, may occur, which you need to work through.

First, to remove the filament from the nozzle. Usually you can heat up the nozzle, then retract the filament. However, for more stubborn nozzle blockages, you may need to disassemble the hot end. Once you have just the nozzle and a piece of filament going into it, you can heat up the nozzle (with a cigarette lighter, small blowtorch, or something similar), and pull out the filament. If the filament is broken off inside the nozzle, gently drill it out with a 2mm drill (do NOT use any bigger drill, and stop as soon as you feel it touching metal). Poking a piece of wire into the nozzle itself should remove anything from the actual nozzle orifice, eg if something has been swept down the Bowden tube.

Next, it's trying to work out WHY the filament stopped extruding, and there are a lot of places and reasons this can happen.
1. Insufficient heat. The thermistor should report the temperature pretty accurately, but if the heater block is loose on the nozzle, heat won't conduct well into the nozzle. Make sure it's mounted the right way up (with the thermistor hole nearest the tip of the nozzle), is done up tightly, and the brass tapered nut is done up tightly on the heater block. To check the heater block is getting hot enough, take a piece of filament and touch it on the heater block when it is up to temperature. It should melt.
2. Blockage of the tip, usually due to debris (see above)
3. Insufficient cooling of the top of the nozzle. This can be caused by the hot end fan not working (it must be on ALL the time), or poor contact of the nozzle in the heatsink. It causes filament to melt further up the nozzle than intended, and causes the filament to be harder to extrude.
4. Gap between top of nozzle and end of Bowden tube. Coupled with 3 (above), this can cause filament to swell into the gap. Once it cools, it then forms a plug, and you cant reverse or extrude without melting this first. It should be fairly obvious when you disassemble the hot end, though.
5. Tight Bowden tube. This increases the pressure needed to extrude. Make sure you drill out the Bowden tube ends with a 2.5mm drill, as shown in the instructions.

All of the above relate to the hot end. You can test the hot end independently of the extruder; disconnect the Bowden tube from the extruder, and manually push filament into the tube, with the hot end up to temperature. It should be reasonably easy to push filament through, and extrude material through the nozzle.

Then test the extruder, without the Bowden tube connected. Additionally, check:
1. The hobbed insert teeth are clean. Once the extruder has skipped, or ground away on the filament, pieces of filament will be stuck in the teeth of the hobbed insert, and it will slip again on these, rather than pushing the filament. Use a pointy tool to clean the teeth.
2. Check the idler bearing pressure adjustment is not too tight or loose.

There is a general troubleshooting guide to extrusion problems here: [reprappro.com]
This is largely for our other printers, but almost all of the points there are relevant, too.

Ian
RepRapPro tech support

To the above, I should add that the sequence for clearing nozzle blockages (and also for changing filament), such that you can clear it right down to the tip of the nozzle, is:

1. Heat nozzle to operating temperature (200C for PLA)
2. Extrude a little filament, like 10mm (if possible) by hand or via the interface, then set temperature to around 100C (try different temperatures if it doesn't pull out to the nozzle; 90C often works for me)
3. Wait for the temperature to drop to 100C, then reverse filament until it comes out of the extruder drive (about 380mm). You can do this at 600mm/min, or by hand if you wish.
4. This should pull out the filament from the melt chamber, hopefully down to the nozzle, along with any contamination.
5. Cut the contaminated end from the filament, and drive or feed the filament to just before the hot end.
6. Set temperature to operating temperature
7. Command the filament to extrude short lengths, 5mm at 200mm/min, until it squirts out of the nozzle.
8. Repeat steps 1 to 7 as necessary, usually at least a couple of times. If there is not improvement after 5 times, you may need to disassemble and clean the hot end.
9. If you have to disassemble the hot end, try to clear all of the filament out of the hot end before reassembly. You can heat the nozzle up with a lighter (hold it with pliers) to soften the filament, and pull it out. If the filament has broken off inside the nozzle, heat it up and gently remove it with a 2mm drill.

This is from 'Nozzle blockage (also for changing filament)' section, here: [reprappro.com]

Ian
RepRapPro tech support

As PRZ says, to allow for a steeper angle on the outside of the nozzle (90 degrees, which improves overhangs) compared with our previous nozzles (Quick set and one-piece stainless, which have a nozzle angle of 118 degrees, which is the same as the angle of a standard drill tip), the Fisher nozzle does step down from 2mm to 1mm internally, before the nozzle itself, of 0.4mm. This is effectively the same as the E3D nozzle tip.

If you extract filament as in the above guide, you should be able to extract the filament right down to the nozzle tip, as shown in johneato's post earlier.

Ian
RepRapPro tech support