They Like It
Metal Extruder and Syringe Pump by mattmoses is licensed under the Creative Commons - GNU GPL license.
© 2009 by mattmoses
Instructions
The standard safety warnings apply. Low-melt alloys are toxic and hot enough to cause burns and fires. Use them only if you are experienced in a lab environment.
In addition: the nozzle, cup, and plate get dangerously hot. These can cause fires and burns. Operate with good ventilation, never operate the system unattended, and know where your fire extinguishers and escape routes are.
1. Heated Cup ----------------------------------
The cup heaters were purchased from American Science and Surplus ( sciplus.com ) which seems to no longer have them in stock. They were intended for coffee makers or something. By chance, the cups were the right size and resistance (8 ohms) for what we needed. You can probably find something similar at one of the many surplus outfits. For temperature control, a thermistor was JB-welded to the bottom of the cup.
2. Heated Nozzle -----------------------------------
This is a derivative of the old RepRap Thermoplast Extruder V1.1. The copper part of the nozzle is treated with JB-weld, wound with nichrome wire, and equipped with a thermistor as described on the RepRap website here: reprap.org/bin/view/Main/ExtruderMechanicalParts .
The copper nozzle and PTFE adapter have to be machined using a lathe. A drill press or small milling machine, in addition to simple hand tools (files, etc) will come in handy. A standard disposable syringe is cut up and glued to the PTFE adapter with silicone caulk. The syringe top is used as a plumbing fitting to connect to the syringe in the pump.
The little safety pin is important. Without the pin, if the nozzle were to get blocked during use, the syringe pump could generate enough pressure to pop the copper nozzle out of the PTFE adapter, spraying molten metal everywhere. The pin prevents this. It can be tricky to get a good seal between the PTFE and copper nozzle. If needed, you can leak-check the whole assembly underwater using another syringe to provide pressure.
The nozzle mount is made from laser-cut parts and is intended to fit the old-school carriage of an early BitsFromBytes ( bitsfrombytes.com/ ) kit. It is a good idea to make a little stand that will safely hold the hot nozzle while it is not in use.
3. Syringe Pump --------------------------------------
The syringe pump uses a standard disposable 12cc plastic syringe (0.7 inch outside diameter). It is made mostly from laser-cut parts, except for the motor coupling. The motor coupling design could certainly be improved, but we made it with bits we had sitting around and so that is what's uploaded.
You will need assorted nuts and bolts to put the thing together, in addition to 2 microswitches, a Solarbotics gear motor, a 6-32 threaded rod (3.5 inches long), and a 6-32 nut. The syringes have a standard Luer-lock fitting, which allows quick connect/disconnect of the hose that goes from pump to nozzle.
If you bypass each limit switch with a diode, you can create a 2-wire device that acts like a DC motor, but has the limit function built-in.
4. Heated Plate ----------------------------------------
This is a 6 by 6 by 1/4 inch aluminum plate with five 40 ohm, 25 watt power resistors (wired in parallel) JB-welded underneath. The plate has some tapped holes at the corners so you can clamp stuff down to it. In the photo you can see some heat damage to the wiring underneath, indicating that this thing gets HOT when running. Be careful...
5. Electrical Interface to RepRap -----------------------
This system is designed for the older single-Arduino setup. The heated plate and heated cup are controlled by a separate Arduino with PWM Driver running off a 24V supply. The nozzle is a pin-for-pin replacement for the old RepRap Thermoplast extruder. The interface is: 3 leads for thermistor board (+5, ground, signal), 2 leads for motor, and 2 leads for nichrome heater. We use a big rotary switch to select between different toolheads.
6. Parts and Materials -------------------------------------
copper bar stock (0.5 inch diameter)
PTFE bar stock (0.75 inch diameter)
cable ties
hose clamp
JB weld
silicone caulk
superglue (for syringe pump parts)
5-minute epoxy (for microswitches)
3 RRRF thermistor boards (nozzle, plate, cup)
syringes - 12cc disposable plastic syringes (0.7 inch outside diameter)
0.2 inch thick acrylic (syringe pump and nozzle mount)
6-32 threaded rod, 3.5 inches long
Solarbotics gear motor
2 microswitches
assorted nuts and bolts
wire and connectors
