After melting the PTFE insulator yet another time, I’ve built another hot end. This one doesn’t use the PTFE as a stress-bearing part, but only to contain any plastic that may ooze above the top of the heater barrel.
The heater barrel is threaded into the PTFE about 0.25″, just enough to keep it aligned. The PTFE isn’t attached anywhere else, just sandwiched between the washer and the aluminum mounting plate above it.
I also made modular heater and thermistor, ala Makergear.com HeatCore. (I know a good idea when I steal it).
non-load-bearing PTFE
I’ve also ditched the separate nozzle, and used the brass screw as a one-part barrel+nozzle. The opening was drilled with a 0.45mm drill.
No nozzle!
Print quality has improved by a lot, and I haven’t had any problems with the feed pinch-wheel teeth stripping the filament.
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.
The RepRap is a 3D printer that builds small objects out of plastics, by squirting layers of melted plastic out of a nozzle, on to a computer-controlled moving platform. Once a single layer is made, it moves to the next layer up from the bottom, repeating this process until your object is created.
This process is called “Fused Deposition Modeling”, or “Fused Filament Fabrication”.
The end result is a strong plastic part, with a slightly ridged surface.
This is basically the same method used by the Stratasys FDM rapid prototyping machine, which costs around $30,000.
The Chicken & Egg problem of building a RepRap machine is that many of the parts are actually made using a RepRap, so if you don’t already have access to one, you’re at a disadvantage.
I’ve been working on what’s called a RepStrap, that is, it’s not exactly following the plans for a RepRap machine, but can be used to ‘bootstrap’ construction of a RepRap. The end result is the same in that you have a 3D printer, but the construction plans & materials differ.
When starting my build I had a few design goals: appearance, cost, and functionality.
For years and years I’ve been facinated with CNC machinery. There’s something incredibly compelling about the idea that you can design something digitally, with all the “undo” you want, and then have a machine make it for you.
Of course, it’s really not that simple in practice, but it’s still an incredibly exciting thing.
For a couple of years now I’ve been picking up motion control parts whenever I see them available cheaply, even if I didn’t have a particular need for them, yet.
Mid-summer 2009 I found a surplus X/Y table on eBay, put in a minimum bid of $50, and won.
This gave me a pretty good starting point for a light-duty milling machine, I had two axis’s that were more accurate than I’d be able to make myself, with 2 stepper motors. I already had a few stepper motor drivers.
I built a ‘Z’ axis that used bronze bushings sliding on steel rods, driven by 10TPI acme threaded rod. The lead-nut was a chunk of Acetal plastic that I’d tapped threads into using a home made tap.
The first revision used a Bosch Colt 1.0HP router for the spindle, as I’d read online that they had very low runout(ie: wobble) in the spindle. I’d measured the Bosch’s runout at about 0.0035″, which seems pretty good for a consumer grade router.
After making a few circuit boards I realized that I’d need something even smoother, and after a little deliberation I ordered a Proxxon IB/E rotary tool. It was $110, which is a lot to pay for what’s essentially a Dremel(which would have been about 1/2 the price).
Once the Proxxon arrived all my hesitations vanished, I can’t speak highly enough about it. I measured the spindle runout at about 0.0005″. I can turn it all the way up to 20,000 RPM and put it down on the desk, and it just sits there. A Dremel would vibrate itself off the edge of the table within a few seconds. Also, even at full speed, it’s quiet enough that I can run it at night while everyone is asleep. The Bosch was loud enough that I didn’t even like to be in the same room with it.
I was incredibly lax about taking pictures of the build process, but did manage to snap a few after it was done. Please ignore the cardboard-box-dust-suppressor system, I haven’t had time to make a proper box.
A proper shaft coupler handles small misalignments:
Repurposed ps2 keyboard cables used for the motors:
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.
