To make the Mk 2 Extruder nozzle interchangeable, just drill the 3mm central hole right through the brass M6 bolt normally used for the body of the nozzle. You can then fit a nozzle, made as detailed below.
You can do it all with hand tools; the fancy vices and drills are just nice-to haves.
- Smooth file
- Soldering iron and/or small gas torch
- centre punch or sharp nail
- vice, preferably a drill press vice
- disposable vice padding (a thick rag is OK)
- Power drill, preferably a drill press
- Dremel or other mini-drill
- Mini drill reaming bit
- Mini drill 0.6mm bit (you will want a mini drill)
- 2mm & 3mm bits
- fine carbide paper, pref. P1200 grit
- Stiff, fine (<0.5mm) wire for pricking
- Brass or steel wire brush
- 20mm section of M6 brass thread or similar bolt
Take a threaded section of M6 brass - a bolt offcut or somesuch at least 20mm long for ease of handling - and mark its centre point. Do not be fooled by the optical illusion caused by threaded rods. Check your centre.
Drill a 3mm hole into it about 4mm to 5mm without wrecking the thread. Get a brass M6 nut of a minimum 5mm thick for use later; if the nut is much thicker, you'll need a deeper 3mm hole in the threaded section.Then drill another millimetre down using a 2mm drill bit. Drill your nozzle's hole into the bottom of this hole, going in 1.5mm-2mm. As the drill bit does not emerge from the other side of the rod yet, it should be less prone to breaking fine drill bits off - I hate it when that happens.
Now, probe the depth of the 2mm hole. Add on a millimetre, mark that as the edge of where you'll cut the threaded rod, and take it off with a hacksaw or fine grinder disc - don't try tidying the cut just yet.
Screw the rod into that M6 nut about 1/3 the way down it leaving the little hole and untidy sawn-off end pointing out, and solder the rod into the nut without flooding the remaining thread. Use a big soldering iron, or preheat the assembly with a torch, then touch up with a small soldering iron. Do not heat and apply solder at the same time with a torch, or you'll melt the incoming solder before it gets to the workpiece. Let it cool before working further.
Some lead-free solders have a highish melting point. This is good, as it allows us to use a wider range of plastics. It has been noted that some do not wet the surface of the brass easily, making soldering difficult. This was solved by tinning the parts with a small quantity of lead solder, wiping off the excess, assembling and then soldering with lead-free solder.
With the nut clamped firmly in a vice, use a file to take off any exposed thread. If the exit hole is off-centre, now is the time to hack away excess brass so that the hole appears to be in the centre of your nozzle. Even nozzles that are desperately off-centre can be rehabilitated this way- trust me! Just don't take off so much brass that you expose the drilled steps inside.
Then use the file to put a roughly 45 degree taper all the way around, forming a cone with the exit hole at the apex. You'll find it easier to rotate the workpiece than file away from weird angles. You're aiming to have an apex that is less than 1mm across, with the exit hole in the centre. DO NOT file across the hole; shape the cone around it.
When all is shaped, smooth things off with fine carbide paper to make the removal of excess polymer easier.
Now attack the nozzle from the rear with one of those dremel tool bits that looks like the business end of an old-fashioned lemon-squeezer. The idea is to make the inside of the hole taper towards the exit.
Stop grinding when the tip of the tool reaches the nozzle's exit hole. Pause frequently to keep the hole clean, pricking (clearing) it with the fine wire - do not use a pin or you'll enlarge the hole. When done, there must be no debris of any kind left over in the nozzle, or the thing will clog. After checking the nozzle itself is clear one last time, scrub off any excess flux with a wire brush and screw the assembly onto the end of your Mk 2 extruder.
I liked this method because I am a lazy beggar and found with a little practice I could make one quite passably without having to set up the lathe.
If polymer leaks out of the thread where the nozzle attaches to the heated extruder barrel, cut a thin washer from suitably-sized silicone rubber tubing and sandwich it between the nozzle and the extruder barrel.
- Nozzle fitted to a half-finished extruder barrel.:
This version has been reduced in diameter with solder around a piece of fine nichrome wire, which is then removed to leave the vital hole. It is an early attempt and has not yet been tapered:
If cracks do develop, usually due to filing away too much, solder the cracks up generously and re-shape the nozzle so that the flat area around the exit area remains circular. Try not to flood the inside of the nozzle.
-- Main.VikOlliver - 16 Jul 2006