RepRap: Blog

The difference in operation of the no-lathe extruder with different barrel lengths and a heatsink leads me to suspect that the main factor in reducing friction is to reduce the size of the zone where the plastic is actually melting.

As you can see in the photos I've chopped an old CPU heatsink (easily salvaged or made from copper/aluminium stock) into 10mm slices, and clamped a pair around the barrel. There is a recess in the middle of the two halves made with a drill 0.5mm smaller than the barrel's external diameter. I have experimented with moving it up and down the barrel. The barrel above the heatsink does nothing useful in this setup, but might be useful for guiding the filament later.


The heatsink stops the plastic melting on entry, keeping the top part of the barrel under 60C. I've rewound the heater to start the coil as close as possible to the nozzle, and to keep the windings close together. Kapton tape is great for this!

Best results definitely seem to be had with a small, powerful heater (1A@13.8V max, running at about 60%) and the heatsink placed as close as possible to the heater windings. This is much more successful than my earlier experiments with heatsinks.

The extruder works continuously, or in bursts, and I checked that it will restart after cooling. It still needs no lathe!

Vik :v)

Labels: melt, no lathe, reprap, zone

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):







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.

Labels: heater, no lathe, nozzle, reprap