RepRap: Blog

Managed to blow the 4.7 Ohm filament at around 200C. By this time the wires were red hot, and a weak spot blew under the Kapton dammit. No matter, I have a New and Improved 6 Ohm version, all-ceramic insulation with double-twisted nichrome on the inputs to ensure a lower temperature on the input lines. I think it is those local hotspots that cause the Kapton to decompose. But hopefully I've just eliminated the Kapton - for the barrel insulation anyway; I might still use it to attach the thermocouple to the barrel for the moment.

Vik :v)

Labels: brass tube, ceramic, extruder, heater, reprap

Finally got over the flu that I brought back from LinuxConf 2010. Mendelssohn is now printing properly with a stepper-driven extruder and a new heating element/barrel design. This is essentially the old hack using a radio aerial and a heatsink. The M4 nozzle (not shown) fits inside the feed tube, so increased pressure forces the nozzle into a shoulder at the end of the tube. So the more pressure, the better the nozzle seal. The shoulder is created by slowly cutting the tube with a pipe cutter.




I'm dip-coating the 3/16" brass tube in fire cement slurry, drying this, and then wrapping the dry ceramic in Kapton to protect it while I wind on about 6 ohms of nichrome. If the Kapton gets vapourised, the heater element will not then short out on the brass tube. The heatsink traps the extruder as well as cooling the end of it, and also acts as an anchor point for connecting the extruder assembly to the X carriage.

Works so far. No lathe needed, no PTFE, no creep, no leaks.

Vik :v)

Labels: aerial, brass tube, extruder, heater, heatsink, nozzle, reprap

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

sid, who is a regular contributor to the RepRap forums, had an idea to get a soldering iron manufacturer to make a heater barrel assembly for RepRap. He approached a Chinese company with a specification and they sent him some prototypes. He forwarded one to me for testing. It appears that they ignored his specification and just sent a standard de-soldering iron element. Nevertheless it is a nice unit and looks eminently usable.



It works perfectly apart from one fatal flaw, full details in my blog.

Labels: heater