How to replace the nozzle in my hotend assembly?

Question

What should I take care of to replace the nozzle of the hotend assembly the right way?

What kind of data, precautions, tools, steps, and verification are important for replacing the nozzle?

The procedure seems straightforward but tutorials differ greatly and seem often incomplete. Online videos are great but long, sometimes misleading, and difficult to compare if they use another printer model.

For example:

• This Prusa 3D tutorial starts from heating the nozzle to 280 °C, which is dangerous for some hotend setups. Also, it is created around a direct drive extruder, so it does not advise to what to do with a Bowden tube.
• Another Changing Nozzles & Bowden Tubes video seems to be a great tutorial but advises heating only to ~210 °C. So I need to make sure I know my hardware limits first? Should I take something else into account about temperature, or just act by experience, starting from 230 °C?
• Is that heating mandatory, or only when there is residue filament inside? If there is something to consider about replacement nozzle before installing it, or cooling down again, like PID calibration?

So I am looking for a general overview: what should I think of to be in control? And maybe a bit of why, but not necessarily how. (As always, each detail may be a separate study, so please don't to fall into troubleshooting, which could be done in separate questions like E3D V6 nozzle seized into heater block).

Answer 1

Tools

• spanners / wrenches - to turn both nozzles (common sizes are 6-8 metric wrenches)
• spanner / (fitting or adjustable) wrench - to hold a heating block
  • or small vise - to hold a heating block (if you are going to unmount the hotend for operation), with non-flammable soft-jaws,
• screwdriver(s)/Allan-keys - when you need to remove shroud or plan to umount the hotend
• non-flammable tray / plate (e.g. ceramic) - to put removed, potentially hot nozzle aside
• adequate personal protective equipment - against getting your fingers burned, etc.

Precautions

Beware of touching heater and thermistor wires with tools during operation. Electronics can be damaged by shorting the heater leads, thermistor leads, either with tools, the nozzle, or even a metal bed. Also, neither 12 V nor 24 V are pleasant to touch.

Using tools with plastic shielding can help to prevent this, but proper care is needed. Improvised rubber or tape wrappings are not advisable.

Step 1: Unload

Before swapping the nozzle, remove the filament. Follow the procedure of your manufacturer, though often this is heating the nozzle, then triggering the Swap-Filament or unload routine.

Many makers suggest a cold-pull. This is heating up to about the print temperature, then going back to off. Letting the filament cool by about 20 °C, they then yank hard at the filament, removing most of the plastic from the nozzle and melt zone. It is not applicable to some nozzles, especially those made from several parts (e.g. Olsson Ruby).

I have found it easier to put in an intermediate step of removing the whole hotend and use clamp it in a small vise to hold it on the heater block. This holds it steady and removes any stress from the heartbreak. However, this is more involved than using a fitting wrench to steady the heater block.

Step 2: Remove the nozzle

Dismount the extruder shroud if it blocks the way to the heater block, or hasn't already been removed to get the hotend dismounted.

If you have a lined hotend, remove the PTFE tube.

If you had oozing, this usually has glued the nozzle and heatbreak to the heater block. Heating the hot end to about the glass transition temperature of the filament will often make it easier (or possible) to remove the nozzle without stress to or damage to parts.

Now use a suitable wrench to remove the nozzle. Make sure to steady the heater block during this step. Otherwise, you might shear off a necked heatbreak, while lined heatbreaks might get deformed.

A Hot removed nozzle needs to be put aside on the safe surface or remain in the block with some windings.

If you work in a vise, you can remove the heatbreak too.

Step 2.5: Cool down

It's best to let the hotend cool down, so you can easier handle the parts. Unless you had to fight with oozing, you can have the nozzle col down still halfway in the block and then do the last windings by hand on a cold nozzle.

Step 3: Install new nozzle

Now, screw in the new nozzle hand tight. There should be at least half a millimeter stick-out between the nozzle flange and the heater block and it needs to butt against the heartbreak. (Nozzle must tighten against the heat break and not stress the heater block). Don't use a wrench yet, just hand tighten the nozzle against the heartbreak.

If you have a lined hotend, re-install the Bowden tube until it butts against the nozzle.

Step 4: Hot tighten

Heat up the hotend to your limit temperature:

• Generally: do it at the highest temperature you will run. Otherwise, you will not get a good seal between the nozzle and heat break if you depending on tightening at lower than operating temperature. A bad seal allows the filament to leak out (oozing). Do not exceed the limit for your hardware.
• For an all-metal hotend (a heat break without Teflon), this is dependant on your heater cartridge and thermosensor.
• For a lined hotend that is 245 °C. Teflon will degrade at 250 °C. This also applies to Bowden tubes that run all the way to your nozzle. Go to the maximum temperature for operating with your machine, then you usually clamp the Bowden tube in place so that it forms a good seal.

Now use the wrench to tighten the heated nozzle carefully. Use a second wrench to steady the heater block, if you don't have the setup in a vise. Don't waste too much time, but don't over-torque!

The exchange is done. If the hotend was unmounted, remove it from the vise, reassemble it fully and install it on the printer again. Make sure that your hotend cooling fan does put the heater block in the airstream.

Step 5: Validation

Run some filament through installed hotend. Observe if there is no ooze outside the nozzle.

Step 6: Finishing

If not already done, mount back the extruder shroud and any parts that had been removed.

Check homing of the Z-axis, as you will need to adjust the Z-height. If you have a sensor on the carriage, you might need to adjust its height to compensate for a slightly altered stickout of the nozzle.

Answer 2

The exact procedure depends on the design of the printer.

After unloading filament, remove and install the nozzle at the highest temperature you will run. Otherwise, you will not get a good seal between the nozzle and heat break if you depending on tightening at lower than operating temperature. A bad seal allows the filament to leak out (oozing). Tighten and untighten the nozzle with wrenches on the heat break and nozzle. The heat break is easily damaged if tightening too tight into the heat sink, but you need a tight connection between the nozzle and heat break. This means the nozzle must tighten against the heat break and not tighten against the heater block; thus space between the nozzle flange and heater block when tightened against the heat break.

Note: If you had oozing, it will glue the nozzle and heat break to the heater block. Heating the hot end will often allow you to remove the nozzle.

Note the electronics of some printer models can be damaged by shorting the nozzles to heater leads, thermistor leads, or even a metal bed. Check for your model.

Running the hot end at 250 °C or above requires an all metal hot end (a heat break without Teflon) or the Teflon will degrade. This also applies to Boden tubes that run all the way to your nozzle. Look for instructions related to your Boden tube. Go to max. temperature for operating with Boden tube, then you usually clamp the Boden tube in place so that it forms a good seal.