Monday, May 11, 2009


The No-Lathe Barrel & Nozzle

In true Open Source fashion, I've been distracted by the attention given to extruders without a lathe and I've figured out how to make an extruder barrel and nozzle without one too. I used some handy but unlikely pre-formed components: A telescopic radio aerial and a posidrive machine screw. To repeat the trick, you'll also need some PTFE tape, kapton tape (or fire cement), 3mm inside diameter silicone tubing, nichrome wire, nuts, bolts, and bits of MDF or similar wood product.You will need a drill that can reliably make a 1mm hole – finer if possible – for the nozzle's exit, plus the usual hand tools. The coil of wire on the right is an improvised rheostat made from the guts of my expired fan heater (thanks for expiring it, Kate).

I Started by dismantling the telescopic aerial, removing the base and very tip so I could slide all the bits apart. Find the tube that is a snug fit on an M3 or M4 posidrive machine screw. Note that one of the ends of the tube has a shoulder turned over on the end of it that stops the other bits of aerial slipping through – this will be the nozzle end. Chop off 50mm of tube and smooth the cut end.

Economic note: More tubes with shoulders can be made by cutting lengths with a a pipe-cutter and gently hammering the cut end over, allowing one to make several barrels from one aerial.

Anchor the posidrive screw in a bit of wood with a nut to make it easier to clamp or handle. Using the dimple in the top, drill 5mm into the screw. Make a 1mmm one first and try finer ones when you get the hang of it. Lubricate with thin oil or WD40 and keep the swarf clear. When you're done, clamp the screw in a vice, file of the head and make it a bit pointy so you're left with something that looks a lot like the one below (it's standing in a nut so I could take a decent picture):

Hack off the top 5mm of the screw, tidy it up, and drill a shallow 2-3mm hole on top of the small hole you exposed with said hacking. You should now have something like a little grub screw with a hole through it. Why not put a hole through a grub screw? 'Cos I got no M3 or M4 grub screws. That is your nozzle.

So wrap the little beast with PTFE tape and pop it down the barrel that you cut off the aerial pointy end first. It should wedge itself in the shoulder at the other end. If you push too hard you'll deform the barrel and pop the thing out the other end. Bad move.

Insulate with kapton tape, add 6-7 ohms of nichrome wire near the nozzle, insulate again. That's your heater.

Slip 10mm of a 25mm length of 3mm ID silicone tube over the open end of the barrel and clamp it all in MDF. I found it necessary to add an MDF slip over the top part of the silicone tube later on to stop the soft plastic bulging within the tube. I used bolts to connect up the power to the nichrome and kapton-taped a thermistor probe to the side. The combination works well up to about 180C with PLA and is stable at temperatures of up to 300C by which time the PLA starts coming out as smoke rings. Surprisingly, the silicone stops the MDF from burning.

So there you have it. Easy to get bits, easy to make, no lathing.

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Brilliant stuff Vik.

So - is the nozzle 'grub screw' just held in the end by pressure and gravity?
Nice work.
I found that you can get brass tube from model shops about that diameter. I was fiddling with external nozzles, though - I like your solution.

a pipe clip could apply some pressure to stop the tube pulling out.

The 'lathe' problem is significant for those of us without access to machine shops - thanks :-)
Brilliant work on simplifying the process. The less specialized tools needed the better. I consider myself a crafty person but have no access to a lathe. Cheers!
@Adrian: From the picture of the nozzle in the barrel, it looks like the fire cement might be used to hold the screw in place.
Adrian. Pretty much. The nozzle/grub is just held in place against the shoulder of the tube by gravity, a little bit of wedging by some PTFE tape (not fire cement, sorry Jay) and the force of the incoming filament.

If the barrel isn't loaded, it is possible to smack the thing hard on a wooden block and extract the nozzle, or after use to push it back out from the other end to maintain it.

Vik :v)
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