After melting the PTFE insulator on my RepStrap extruder twice, I went back to the drawing board and replaced the whole hot-end assembly.

I manually turned the new nozzle and barrel on my mini-lathe. The nichrome heater wire will wrap right around the nozzle, applying the heat as close as possible to the tip.

The heater-barrel has a reduced outer diameter, my theory being that less metal there will reduce the flow of heat up into the PTFE insulator.

Here are a few pictures.


Extruder nozzle, with channel for nichrome.

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This is Van de Graff machine I built in 2006. It’s made of some plexiglass tube, and two mixing bowls.

The rollers are Delrin and teflon, as you want to use materials from opposite ends of the triboelectric scale.

The base is 1/2″ plastic that I heated with a torch and bent,

The rollers and the roller-support pieces were turned on my mini-lathe.

The axles are made of 8mm drill rod turning in skate bearings.

The belt is made from a piece of Theraband, basically a big sheet of rubber used for exercise. It’s glued into a loop with contact cement.

The motor is a surplus DC motor, powered by a 24v DC power supply. I think the power supply was originally for some part of a phone system, I picked it up at a local freight-salvage store.

I put an AC light dimmer inline to adjust the input power to the AC-adapter, which works pretty well to adjust the motor speed.

One problem I did run into was that all the static building up would cause arcing within the power supply, so I broke it open and insulated everything with silicone caulking. Probably not the best thing for the cooling, but I never really run it for more than a few minutes at a time, so I haven’t had any problems.

I built a mounting for the motor and speed control, but I don’t have any pictures of it, hopefully I’ll remember to take some.

Here’s a few pictures.

my Van de Graff generator, made from some junk I had.

Here’s a picture of some sparks, this was a 15 second exposure, and the sparks arc up to two inches when it’s runnning well.

Long-exposure pic of Van de Graff discharges

Things that affect how well it works are mostly humidity, and how clean the ‘sphere’ is. Any dust causes sharp points where the electrons will ‘leak’ off, so for best results I’ll wipe it down first with some alcohol and a lint-free microfiber cloth, Supposedly it also helps to cook off any moisture by using a hair dryer, but I’ve never bothered to try that.

One more picture.

static electricity is hard to photograph

Last week I did a test pcb milling on my cnc pcb mill. I’m still learning how to properly configure the PCB-Gcode software, and I think this is the best result to date.

The board is the top side of LadyAda’s Drawdio board, and it took about 15 minutes to mill. I used a 60 degree pcb bit I got from a Chinese seller on eBay. Before drilling the holes I ran through the drilling gcode, once with the pcb bit still in the spindle, at a higher depth. Basicialy this drills shallow pilot holes through the copper, but not through the PCB. This helps reduce the amount of “walking” that the tiny drill bit does when it’s drilling the holes.

The holes are still off-center a bit from the pads, I’m still trying to figure out why that is. One possibility is that I accidentally twisted the router in it’s mounting when I changed from the pcb bit to the drill bit.


Milled pcb, with a dime for scale.

pcb pad/hole alignment at 100x magnification.

One more picture, after a little cleanup with some 1500 grit sandpaper, I think it came out pretty well.

after some cleanup with 1500 grit sandpaper.