Glass Nozzles

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Glass Nozzles

Release status: Experimental

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Description
Glass Nozzle to replace PTFE/Brass combination
License
GPL
Author
Contributors
Based-on
Categories
Extruders, Nozzle {url = N/A
CAD Models
External Link



The Glass Nozzle page is a tutorial on how to build and mount Glass Nozzles

One of the most frequently described failure modes for a working reprap is an extruder failure. This often occurs because the brass nozzle works loose in the PTFE thermal break, or slight mismatches in drilling create choke points that jam. Using a single material for both nozzle and thermal break would greatly simplify the construction of extruder nozzles, eliminate the drilling mismatches, and reduce or eliminate the nozzle working loose from the thermal break. Recent discussions about reducing the heat flow from the nozzle to the ABS mounting bracket pointed out that even stainless steel, a very poor conductor of heat, was still way to good for any normal length nozzle. The only way to reduce the temperature of the stainless steel tube in that short a distance is to add many washers or other heat sinks to cool the metal before it melts its mounting bracket. But this cooling wastes lots of power, and releases heat inside the reprap where it does no good. The only solution so far is to use glass or ceramic nozzles. Ceramics can be machined, but not formed or molded,and we are limited to ceramic nozzle shapes already produced. The glass can purchased in bulk and worked with a welding torch to create a very orifice. It can be made easily in two forms, one a blunt nosed tip in which the glass closes off the interior hollow by surface tension, and creates a blob tip that can be ground down until reaching a funnel shaped section, and then ground further until the desired orifice size is reached. The other is to heat the glass tubing in the middle and draw it out, just like making a micro-pipette. This can also produce small orifice sizes, but leads to very thin walls at the tip also. The blunt nosed nozzle is very strong and should be able to resist breakage even after a Z axis crash. The drawn tip is not a strong and may break. Both types can be fitted with a flange at the other end to make a simple saddle clamp a secure mount, or left as is for compression fitting mounting.

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This page present methods to wire up a glass nozzle, and to build simple mounts for them

Everything below this point is working notes.

Wiring the nozzle

Step 1

Here is a photo of the material needed to start. A glass nozzle, of course. This one has a flange and index key as well. Scissors to cut the Kapton tape as well as the Nichrome wire. A thermocouple has been prepared from extension wire by twisting and soldering the tip. A multimeter that read both ohms and degrees C from a Type K thermocouple.

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Description Quantity
glass nozzle 1
Kapton tape 1" 1
nichrome wire #30 1
thermocouple 1
Ohm meter 1
scissors 1

Here is a complete list of all the parts and materials and tools needed.

Step 2

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Cut off a 10 ohm length of nichrome wire. This will set the maximum heating rate to be 15 watts. For 30 gauge nichrome wire, this is a length of about 12 inches or 30 cm. The wire is so thin it is hard to see in this picture. Use the ohm meter to verify the resistance before you start. Remember the value, as we will check it again when done to test for shorts. Also make sure your thermocouple is ready to install. You can simply strip the ends of the thermocouple extension wire and twist them together, but it is better to solder or weld them together so that there is never any loose of continuity. Since the voltage differential is generated by the temperature change across the each wire, it does not matter if they are soldered together instead of welding. But don't splice any other type of wire to the thermocouple to extend it to the electronics. If you must extend it, use more thermocouple wire.

Step 3

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Cut a piece of Kapton tape long enough to go at least twice around the glass nozzle. Start the first little strip to get it securely bonded to the glass nozzle. Place the edge as far down the nozzle as possible. To get good flow rates, the very tip needs to be hot, and unlike the brass nozzle tips, glass does not easily conduct extra heat here. Having the tape all the way down means that the first few loops of nichrome wire will be that far down, too.

Step 4

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Insert the thermocouple first. It is th emost difficult to keep in place, and needs the strongest taping. Notice that the thermocouple wire and the glass key index match up. This will help later when mounting the nozzle.

Step 5

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Pull the tape firmly to get a good hold on the thermocouple, go about half way around and then stop. Now place the nichrome wire cut off in step 2 so that one end just sticks past the top of the nozzle. This will allow connecting it to the power leads using the same bolts that hold the mount the nozzle to the extruder base. The long end should run straight off the tip of the nozzle. Once again, the edge of the tape should be as close to the tip of the nozzle as possible.

Step 6

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Finish wrapping the tape on to the nozzle. This will hold the thermocouple and the starting point of the nichrome wire spiralling back up the nozzle.

Step 7

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Prepare the second piece of Kapton tape BEFORE you begin winding. Once you have the wire tightly wrapped around the glass, you will not be able to let go until the loose end is secured.

Step 8

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Now coil the wire as tightly as possible without have one loop touch another and short out a section. Don't worry too much if this happens once, but if it happens in several spots, stop, relax, and start over. You want to have as many loops as possible close to the tip. When you get near the other end of the wire, start spacing out the loops much further apart with each loop. This will cause a more gradual drop if glass temperature and reduce the chance of thermal stress induced breakage.

Step 9

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This is what the completed nozzle should look like. At this point, both the heater wire and the thermocouple are installed, and should be ready to wire up. You may decide to wrap some extra layers of Kapton tape around the heater section to provide insulation, or you may wrap fiberglass or other high temperature insulating material around the heater wires to keep the heat in.

Step 10

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To verify that the nichrome wire coils did not short each other out, test the resistance of the wire again. It should be fairly close to what you had before wrapping it. If it is too low, pull off all the tape and start over because the coils are partially shorted out and the heating will be very uneven.

Mounting a Flanged Glass Nozzle

Step 1

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The simple way to mount a flanged glass nozzle, and also works for an unflanged one too, is to cut out a block of wood and use it to make a saddle clamp for the nozzle. Start with a block that is 4x3x2 cm, with the grain running in the longest direction. I ended up shortening the 3 cm side a little to keep the bolts from being too long, but don't go under 2.5cm. I am fortunate to have a band saw to do the cutting, but this is not precise work, and can easily be done with a hand saw.

Step 2

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Find a drill bit that is very close in diameter to the outside of the glass nozzle, which should be around 8mm. It does not have to be exact, and it is probably better to be slightly too large than slightly too small. Drill a hole in the center of the 4x3 side. Once again, a drill press is nice, but a hand drill will be adequate. This hole deterimens what angle the glass nozzle sticks out of the bottom of the clamp, so try to get it perpendicular. But don't worry if it isn't, once rigidly mounted, the nozzle position will be repeatable, even if slightly off the true center.

Step 3

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Here I have placed the glass nozzle next to the hole. It would be nice to place it into the hole now to check the size, but now that there is heater wire on one end, and the flange on the other, we can not test it until we cut the block in two.

Step 4

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Next flip the block on its side so that the 4x2 side is exposed. Drill two smaller holes for the two bolts to go through. I used 1/4 20 bolts, which on reflection look over sized for the job. You might prefer #10 bolts or 4mm bolts. Drill one hole on each side, far enough out that neither hole intersects the hole for the glass.

Step 5

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Place the bolts into the bolt holes to verify that they are long enough, and that they will not interfere with the glass nozzle.

Step 6

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Once all the holes have been drilled, you are ready to cut the block in half and make it a saddle clamp. Once again, a band saw is nice, but a hand saw will suffice. You also don't need to worry about a thick cut, because you want some space between the pieces so that when you tighten the bolts it holds on to the glass.

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