Clearing nozzles

Safety / Disclaimer
WARNING: Use all saftey considerations when working on your printer. Failure to do so can result in personal injury and/or damage to the equipment.

In Place Cleaning
Check out Whpthomas's post at Thingiverse for a tool and tips about cleaning the nozzle without having to remove it.

Removing the Nozzle

 * 1) Unload the plastic filament.  While this may not always be needed, it does help in keeping the process to a minimum of fuss and frustration.
 * 2) Heat the nozzle to near printing temperatures.
 * 3) Use a pair of pliers, vice grips, or other gripping tool to hold the heating block securely in place.  Take care not to pinch any wires.
 * 4) Use the right sized wrench for your nozzle.  (Replicator 1&2 designs use a 7mm wrench.)  Use this wrench to twist the heated nozzle counter clockwise to unscrew it.
 * 5) Use a scrap cloth or a metal container to catch the nozzle when it finally comes loose.
 * 6) If you have a spare nozzle, thread it onto the printer and secure it with sufficient torque.  Be sure to check your build platform's levelling afterwards and ensure the gaps are correct.  Take care that the nozzle does not crash into the platform - the nozzle may not be sitting at the same height as the old one.
 * 7) Turn off the heat on the printer.
 * 8) Allow the nozzle to cool before handling it with your fingers.

The quick way - ABS and/or PLA

 * 1) You'll need a blow torch, welders gloves (or something to protect your hands from the flames/heat), and a long handled set of pliers.
 * 2) Light the torch.
 * 3) Use the pliers to grasp the nozzle.  Position the nozzle so you can direct the flames into the inside of the nozzle.
 * 4) Use the blowtorch to burn away the plastic in the nozzle.
 * 5) Take care to NOT overheat the nozzle.  Too hot and it will deform/melt.  (I know of at least one person who has destroyed a nozzle this way.)
 * 6) You know you are done when you can see through the nozzle.  Position the nozzle with the hole pointing at a light source - you should see the light through the hole.
 * 7) Turn off the blow torch and allow the nozzle to cool.
 * 8) Use a toothbrush and/or water to clear away any remaining ash or plastic.
 * 9) Repeat the process if needed.
 * 10) When finished, it is advisable to manually rub a .4mm drill bit or carefully filed sanded needle (use calipers to verify diameter) through the nozzle to ensure it is perfectly circular.

When using ABS
ABS plastic disolves in Acetone. However, the outer parts of the plastic will protect the inner parts. So, the Acetone needs to be agitated periodically and the melted plastic cleaned up/removed from the nozzle.
 * 1) You will need Acetone.  You can find it at your local hardware store.  It should be pure acetone for the best effects - some nail polish removers may suffice, but some are too weak.  Use the Acetone in a VERY well ventilated area - too much exposure to the fumes may cause respiratory distress, iritated eyes, nausea, and other medical concerns.
 * 2) You will also need a  glass jar with a sealable lid that is not affected by Acetone.
 * 3) Soak the nozzle in Acetone.
 * 4) Every hour or two (you will not hurt the nozzle if you leave it in there for extended periods of time):
 * 5) Swirl the acetone around for a short while.
 * 6) Remove the nozzle from the jar.  Use a rag and/or your thumbnail to wipe away the crude on the outside of the nozzle. The acetone will evaporate quickly, so you'll only have a few moments before you need to soak again to do further cleaning on the outside.
 * 7) Use a small wire to gently probe and remove plastic from inside the nozzle.  Be careful to not scratch or damage the nozzle.  Wipe the wire off on a rag or napkin (to be disposed of later).  Repeat the process until the acetone evaporates and you can't get any more plastic from the nozzle, or until the nozzle is clean.
 * 8) Put the nozzle back in the jar to soak some more.
 * 9) You will know you are done when you can see through the nozzle and see that the opening is unobstructed. Hold the nozzle between you and a light source - if you can see the light through the nozzle and there are no obstructions, you are probably clean enough.  If desired you can do an additional test by rinsing off the nozzle in water and trying to blow through the nozzle.  If air is slowly escaping the nozzle, then you are probably done.  (don't forget the rinse - acetone tastes bad!!)

When using PLA
PLA does NOT disolve in Acetone. Do NOT put a nozzle with PLA in it into acetone.

nb: yes it does it just takes a lot longer. I'm watching PLA dissolve off a hardened steel nozzle in acetone as I write this. Are there any negative side effects from doing this? Why the 'Do NOT' in caps? Is this a warning or did you merely think it wouldn't work?

Other than the "quick way" above, I am not aware of any method to clean PLA that does not involve caustic sodas. The recommendations I've seen is to simply heat the nozzle and the "load filament" for an exdended period of time (5 to 15 minutes?) to clear away debris and old plastic.

I put the Nozzle into Tetrahydrofuran. It solve PLA.

Remounting the Nozzle
Once the nozzle is clean, or you have another nozzle to use, you can simply (re)mount the nozzle by threading it into the hole. You should not need to heat the print head to do this. Take care to ensure the nozzle is not cross-threaded. Use the wrench to tighten the nozzle as much as needed. It should be snug, but not any tighter or you risk stripping the aluminum block. If you have dual nozzles, raise your platform to a point where it is just touching the lower nozzle. You can tighten/loosen the target nozzle until both nozzles touch the platform at the same time. (and thereby ensure the nozzles are at the same height). One note on this - if your nozzle is too loose, you may get plastic escaping at the top of the nozzle threads and flowing into the surrounding area (heater resister, ceramic  insulator, etc.)