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Wildseyed Simple Hot End

by wildseyed, published

Wildseyed Simple Hot End by wildseyed Apr 15, 2011
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Summary

This is the result of my efforts to produce a reliable hot end for RepRap, using minimal components and tools. In it's most recent incarnations, you no longer need to tap threads for the MIG welder tip, make the nozzle clamp, or cut a slot for the power resistor.

The original instructions are on the RepRap Wiki (http://reprap.org/wiki/Wildseyed_Simple_Hot_End), but I'm not wiki savvy, so I think I'll be posting the progress here first from now on, and updating the Wiki with well tested results.

Instructions

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 Auto Hose Female Coupling (these are a little different from air hose couplings) with 1/2" ID 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 (Save yourself from cheap, thin tape that won't stick, and buy it from MCmaster)
1 - Small Shrink Tubing for insulating Thermistor Leads

Tools Required

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.

  1. 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)

  2. Cut into the hole from the 3/8" x 3/4" side. (optional if doing a press fit)

  3. 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)

  4. The power resistor can be mounted in at least three ways:

A. You could screw it into the top of the block with a couple of M2 screws.

B. 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.

C. My current favorite. Put some heat sink compound on the block, place the power resistor on top, and secure with Kapton tape (The thick good kind).

The Nozzle and Heat Barrier

  1. Clamp the brass auto 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.

  1. 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.

  2. 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.

  3. Insert the copper tip into the drill press chuck, threaded end pointing down, and secure tightly.

  4. Set the drill speed to the slowest setting. 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.

  5. 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.

  1. Screw the copper tip onto the brass coupling if not press fitting it.

  2. 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.

  3. Running the drill press, take some sand paper, and sand a slight taper into half of the rod, up from the bottom.

  4. 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. I actually use a sharp chizel tip to shave it down quickly.

  5. 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 and secure the coupling nice and snug.

  6. 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 the first time I did it, so I put the whole thing on the drill press and reamed it out abit. In other attempts, the extruder mounting holes were spaced farther apart, so it was not a problem.

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. This eliminates problems with solder melting, etc.

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Mig welding tips ay... 0.6mm is the smallest, so i guess people will start buying these up to test with :)

What I do now with the MIG tip is to tap them into the brass coupling with a hammer. As the tip begins to flatten out, the hole becomes smaller and smaller. When I feel that it looks small enough, I stop, and sharpen the tip using sand paper, the chisel, and anything else I have handy.

Great work, it would be good to give source and part numbers for all parts. My wade extruder has a 5/8" hole on the bottom, so I would need to have a bigger PTFE Rod.

Actually, my Wade's is the same. It does not have to fit tight in the hole. The set screws do all the work!

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