Wildseyed Simple Hot End
This simple hot end design, while still a work in progress, works very well, and I encourage everyone to try it, and improve on it. The primary objectives of this design are to reduce the number of specialized tools and materials required to fabricate a hot end extrusion nozzle for RepRap and similar machines, to keep the part count to a minimum, and to provide a simple mounting method that is reliable under pressure.
B.O.M. From Top to Bottom 1 - 1/2" PTFE Rod cut to a length of 40mm (Forgive me for mixing SAE and Metric) 1 - 1/4" Brass Air Hose Coupling with 1/2" threading on the large end. 1 - MIG Welder Tip - Copper - 0.23mm or 0.30mm 1 - Block of Aluminum 1.5" x 0.75" x 0.375" (1-1/2" x 3/4" x 3/8") 1 - Dale 91637 Power Resistor - 10 Watts 5.11 Ohms 1% 1 - 100K Thermistor 1 - #6-1" Pan Screw (optional if doing a press fit) 1 - #6 Lock Nut (optional if doing a press fit) 2 - Aligator Clips With leads soldered on - Small ones are best 1 - Roll Kapton Tape 1 - Small Shrink Tubing for insulating Thermistor Leads
Drill Press Vice Pliers 3mm Drill Bit 1/8" Drill Bit 7/16" Drill Bit Small Table Saw Tap and Die for 7mm (optional if doing a press fit)
Construction and Assembly
Heater Block and Nozzle Clamp
1. Drill a 7/16" hole at one end of the aluminum block, 1/2" from one of the the 3/8" x 3/4" ends, through the 1-1/2" x 3/4" side.
1a. If you would rather press fit the aluminum block onto the brass coupling, make the hole a size smaller, and use the drill press and some sand paper to taper the end of the coupling slightly.
2. Drill a 1/8" hole through the 1-1/2" x 3/8" side of the block, 1/4" in from the end where you drilled the 7/16" hole. (optional if doing a press fit)
3. Cut into the hole from the 3/8" x 3/4" side. (optional if doing a press fit)
4. Insert the #6 - 1" pan screw into the 3mm hole, and secure with the #6 lock-nut. This clamp will hold the heater block onto the brass air hose coupling. (optional if doing a press fit)
5. The power resistor can be mounted in a couple of ways. You could screw it into the top of the block with a couple of M2 screws, but my preference is to use the table saw to cut a 10mm slot into the top of the block, at the opposite end from the tip clamp. The slot is just a hair narrower than the power resistor, and about 4mm deep. Once the slot is cut, apply a little heat sink compound, and use a vice to press fit the power resistor into the block.
The Nozzle and Heat Barrier
1. Clamp the brass air hose coupling in a vice, and thread the narrow end of the coupling with your 7mm tap.
1a. Instead of threading the MIG welder tip, you can use the drill press and sand paper to taper it, and then press fit it into the brass coupling using a hammer. This has the additional benefit of reducing the size of the hole in the tip from 0.8mm to 0.3mm, or less! It might take some practice to get it just right if you are not particularly handy with a hammer, so buy extra tips.
2. Clamp a block of wood, or scrap metal onto the drill press, and drill a 3mm hole into into it, close enough to the edge so you can insert a set-screw or two from the sides. Later, you will clamp your 3mm drill bit in this hole to drill out the center of the copper nozzle. Do not remove this block from the drill press unless you can make sure it goes back to the same position later.
3. Clamp the MIG welder copper tip securely into your vice, tip pointing down, so that the threads (not 7mm) and some of the smooth surface of the tip are exposed. Put a 7mm thread on this. Vice grips work here too.
4. Insert the copper tip into the drill press chuck, threaded end pointing down, and secure tightly.
5. Drill the copper tip down onto the 3mm bit. This should go into the center of the nozzle. Do not use too much pressure. The copper is very soft. Drill almost all the way through, leaving just 0.5mm - 1.0mm on the end.
6. Flip the copper tip in the chuck, and use the sand paper to sharpen the tip to a point. The sharper the better.
6a. If you press fit the MIG tip into the brass coupling, you will have to wait until the PTFE rod is screwed on to the coupling, and then mount the whole thing in the drill press. This is only true if your drill press has a 1/2" chuck.
7. Screw the copper tip onto the brass coupling if not press fitting it.
8. With the 3mm drill bit still secured in the block jig, mount the PTFE rod into the drill chuck, and drill a 3mm hole right through the center.
9. Running the drill press, take some sand paper, and sand a slight taper into half of the rod, up from the bottom.
10. Using the same technique, sand down the last 10mm of the PTFE to a diameter of 3/8". This part will fit snug into the bottom end of the coupling when heated.
11. Screw the PTFE into the brass coupling, using a pair of pliers to hold the PTFE. It should not be really tight. The PTFE will expand when it warms up.
12. Drill another 3mm hole into the block for the thermistor, but don't go all the way through. Insert the thermistor, and secure using the Kapton tape. Use shrink tubing to insulate the thermistor leads.
Mounting the Hot End
My version of the Wade's Extruder had four holes coming into the hot end hole from the sides. I don't know much about where this came from, but I assume this was for mounting a piece of PEEK on some other hot end design. I used four set screws to clamp on to the PTFE here. This compressed the 3mm hole in the PTFE, so I put the whole thing on the drill press and reamed it out abit.
Apart from these four set screws, nothing else holds my hot end onto the extruder body. Really! I have not had any problems with the hot end falling off, and even when it's hot (250C), there is little or no movement, or warping.
Use the alligator clips to connect directly to the power resistor on either side.