A riveting read

A recent modification to the RepRap extruder is the addition of two 3mm pins through the clamp and the PTFE insulator to prevent the PTFE slipping out. My PTFE tube is only 12mm diameter compared to the current design which is 16mm so 3mm pins are a bit too big for it. Instead I used some shafts from pop head rivets which are about 2.3 mm.



I drilled the holes 2.2mm to make them a snug fit.



Here are the pins installed through the clamp after being cut to length and rounded of with a grinder:-

Nutty Nozzle

My old extruder nozzle was made from a solid brass rod with a 0.5mm hole in the end.



It was drilled 3.2mm from the other end to accept the filament. The problem was gauging how far to drill from the back. Ideally the hole in the end should be as short as possible to provide less resistance to the filament flow. Drilling too far would write it off so I erred on the side of caution.

I suspected it was a bit on the long side as I got more die swell than I was expecting. Since it is now scrap I sectioned it to find out exactly how long the hole was. It turns out it was about 0.6mm.

The latest RepRap design uses an acorn nut which gives much better access to the back of the hole. I used the smallest drill I have, which is 0.3mm, to start with, I might open it up later.



The dome of a brass acorn nut is quite thick so I opened the hole out from the back using a conical milling bit that I bought for PCB track isolation milling.



The point is actually about 0.3mm so I was able to countersink the hole from the back until the point came through. That means the rim of the hole is very thin indeed and there is a double taper leading to it. The first is created by the drill that made the thread hole in the acorn nut and then a shallower taper made by my mill bit. It will be interesting to see what flow rate and die swell I achieve with this close to ideal shaped aperture.



I turned down the front of the nozzle to a point to give some clearance to the work piece as suggested by Vik Olliver somewhere I can't find now.



The extra hole on the face next to the thermistor is to allow me to introduce a thermocouple during calibration.

J-B Weld Heater

I ordered some Cerastil H-115 high temperature ceramic glue today but it will not arrive for a few weeks so I made another heater with J-B Weld. It is much quicker and easier than using BBQ paint.

I spread a thin layer on the barrel to insulate it and left it for 6 hours to set. Last time I used a thicker layer and turned it down but this time I just spread it very thinly with a spatula while hand rotating the lathe.



Next I wound the nichrome using a nut with a small hole drilled in it to anchor the start. I anchored the end using a piece of copper wire tied to it and pulled over a support round the back of the chuck. I expect this could be done with a drill chuck if you don't have a lathe.



I then added a second, thicker, layer of J-B Weld and left it over night to set.



Finally I slowly heated it up to 200°C in an oven to cure it.



I haven't tested it yet, apart from checking it for opens and shorts but it is pretty much the same method I used first time around: hydraraptor.blogspot.com/2007/07/hotting-up