Glass nozzles for extruders

An update on my previous ideas:
My mendel is done! it sings and dances, but still needs a hot end.
Here is my progress so far.


(you can see that there is a .5 mm gap between plates 4 and 3. This is because i haven't cranked down on the screws; i'm scared of breaking the glass. the other 3 plates have no gaps between them. what looks like a gap between plates 1 and 2 is actually just a shadow from a horrible cutting job.)

(i drilled the hole for the resistor after i took this last picture, and even though the holes don't look like they line up, they do when properly aligned)

As you can see, i only am using 4 plates (badly cut, but i only have a hacksaw to work with)
the top two plates are for a homemade compression fitting. i used a piece of copper wire, but it is too thick so i had to work it down to size. Not ideal. i'll get smaller wire eventually.
the 3rd plate is a spacer. if you add another spacer, you could place two resistors on each side of the tube horizontally,, drilling a hole between these two spacers. But my arm was tired from cutting the other 4, so i put my resistor vertically :-)
The bottom plate is tapped for 2 m3 bolts. I drilled the center, where the orifice will go, about half way through with a 3mm bit (actually whatever the closest fractional SAE bit is)

my drill press is laughable and just barely adequate for the big holes. I have a .4 mm drill bit for the orifice, but am scared to use it :-)

Maybe a jeweler has an adequate drill press? I'll call around.

One benefit of this design is that the bottom plate can be switched out in order to change orifice size. it would be even better to have a screw in orifice. If i can get a drill press good enough for these micro bit sizes, i'll experiment with that.

The filament is also in direct contact with the aluminum, and the orifice is aluminum, which seems like it will transfer heat better.

Rocket_scientist sent me a flanged glass tube to experiment with the "flange inside the block" idea, but the flange has about an 10 mm diameter. ideally, it would be 8mm or less, and only as tall as one layer (3mm). i think a perfect flange would be ground to the proper dimensions.

The compression fitting holds very well, though, so i don't know if it's worth the extra labor. however, i haven't tried heating or extruding yet. i may find that the compression fitting breaks the glass, or the pressure of the filament slides off the block.

(Also, i was naive to think that a conical bit, like a countersink bit, would drill. all it does is spin and spin, since there are no cutting faces at the apex.)

Edited 3 time(s). Last edit at 10/27/2010 03:58PM by Buback.

Buback,
Do you need a different nozzle? I have a glass grinder, so I can grind down the flange to 8mm. I can also make you one with a tapered tip that id larger than 1mm so that different nozzle plates can be pressed against it and still seal fairly well.

The idea of putting a metal plate on the very bottom to create the orifice and heat the plastic right at the tip is good. I will have to try one of those too. For a screw in orifice, you can not use a set screw because it has the inside hole for the allen wrench. But a very short hex head bolt could be drilled for orifice size and then screwed into the bottom plate. I have some thicker blocks of aluminum that I can drill to fit over the glass, and have threading on the bottom to take a short bolt with an orifice drilled into it. Then the heater resistor and thermocouple can be bolted to the block of aluminum, and maybe some tape or insulation wrapped around that.

Mike

rocket_scientist Wrote:
-------------------------------------------------------
> I have a glass
> grinder, so I can grind down the flange to 8mm. I
> can also make you one with a tapered tip that id
> larger than 1mm so that different nozzle plates
> can be pressed against it and still seal fairly
> well.

That would be great! I'm not sure about the tapered tip though; while it's a great idea, i don't have the tooling to match the taper.

Once my mendel is printing i'm hoping i can improve some of the tools i have at hand.
--
A solid block would defiantly be better. Once i can find a thick piece of aluminum i'll try it. here's a revised sketch(attached).

For the screw in nozzle: it might be difficult to drill into a bolt with such a tiny bit. I was thinking a larger diameter anyway, like 8mm. some leftover studding would work, but the steel drilling would still be a problem (maybe. I don't have much experience with drilling such small holes). Brass M8 bolts?

if you cut or grind two flats on the part of the nozzle that protrudes from the block, you could use a small crescent wrench, maybe even the same size as the wrench included with a dremel.

the removable nozzle would also make cleaning out clogs easier.

Edited 1 time(s). Last edit at 10/28/2010 11:49AM by Buback.

Buback,
I wasn't cleat in my last post. In this case, I was referring not to the drawn out nozzles that I have made, but an unmodified glass tube that is ground down to a cone shape so that it will seal against a brass bolt with a similar taper countersink. I have attached a crude drawing of what I was thinking of. I tried doing this in Google Sketch, but it was faster in Word to do a 2D drawing.

I think there may some advantage to this approach. The metal will be better at heating the plastic, and the hottest part of plastic will be the part inside the narrow orifice. The glass will insulate the incoming filament to minimize the melt zone. With an all-glass nozzle, the friction will be less, but the hottest part is in the middle, the tip tends to cool off.

I am currently pushing to get my McWire built and running, so I may not work on making one of these for awhile, but I think this variation is worth a test.

Mike

yeah i understood you, but i still think my available tooling will be a problem. If i don't drill the countersink perfectly centered, the pieces won't butt against each other and the gap will fill with plastic. I think that you would have to make a matched set of glass and nozzle.
---
I wired up my hot end and gave it a test earlier. The result?: it slid right off after about 3mm of extrusion out the orifice. :-(
I think I misunderstood how the thermal expansion would affect the aluminum block. I thought that, if anything, the hole that the glass goes through would get smaller; in other words, it would expand into the hole, almost like the whole block was swelling. I think it's expanding more like a balloon, where it's just scaling up as it expands, and the hole gets bigger.

if this is the case I'll have to put a lot more force on the compression ferrule in the cold state in order to get any grip when hot. I don't know how much compressive force the glass can take around it's circumference like that. perhaps i'll try abrading the surface of the glass near the bottom, where it grips, and see if that does any good.

this test makes it more likely that a flange will be needed if going with a metal orifice design. I think a compressive fitting at the top will be fine, though, as long as it's far enough away from the heater (how far is that? no clue, yet)

Unless I left some hidden thermal stress, the glass should be quite strong. Especially with a balanced force around the circumference. However, if you break a nozzle following my instructions, I will send a replacement to continue experimenting with. I still think that some form a glass based nozzle is the way we eventually want to go.

Mike

I dont know much about the glass grinding process, but would it be possible to grind a notch in the glass that the compression O-ring could rest in? That would give some mechanical stability for the heater block rather than just relying on friction on the relatively smooth glass.

I think that would be ok, but but i see a couple problems to overcome:
-The ring has to be big enough to slide over the end of the tube. the compression fitting then has to squeeze it into the notch, which might be a lot of travel.
-I just assemble the plates, start the screws so it doesn't fall to pieces, and then set it on a table, orifice-down. then i push down on the glass and tighten the screws. this ensures that the glass is butted against the bottom plate and there are no gaps. A notch would have to be ground in very closely to where the ring will sit in order to prevent a gap. If you have the ability to do this, and a block of aluminum, i'd forgo the ring entirely, grind two troughs 180 degrees opposed, and just put two screws into the block


That being said, on lunch break i went home and abraded the glass some with a diamond dremel bit, and then really cranked down on the screws. wired it all up and i got some extrusion, and the block didn't slide off. At least not yet. Also, last night i put a drill bit into the block, in place of the glass, and cranked down the screws, hoping the form the ferrule a bit more to match the shape of the cutout it fits in. that may have helped as well.

Edited 1 time(s). Last edit at 10/29/2010 05:17PM by Buback.

Just had an idea. When pressing the replaceable orifice against the glass, it is hard to get a precise fit to prevent leaks. What about using PTFE or PEET washer as a gasket? It should be good through the entire temperature range, and compliant enough to seal the gaps if everything to smooth and clean.

Mike

yeah i'll have to use some sort of gasket. i'm getting leaks; damn thermal expansion!

I was hoping that the compression fitting would allow the use of unworked glass, but it seems like it will be a hassle to work out all the kinks. the aluminum expands slightly too much, so i have to tighten the fitting a bit too much, which will eventually lead to fractures in the glass.

I think it is a great low skill level solution, since at most it only requires cutting the glass to length (which is tricky, but probably only takes a couple cuts to get a adequate piece). the problem is that, being low-cost/low-skill level, it will inevitably require more maintenance.

For further development, i'm going to try isolating the compression fitting a bit from the heater. i'm hoping that if i keep it cool enough it won't expand enough to slip off.

I've attached two other designs for evaluation. just quick MS paint doodles. please take a look and tell me what you think.
-block3.jpg - in this design, there is a glass bead around the tube. rocket_scientists work shows that this should be pretty easy to do, with the right equipment. definatly not a low-skill option, and would require a finalized design in order to put the bead in the right place.
-block4.jpg - this design isolates the compression fitting further up the glass tube in order to keep it cool.

Edited 1 time(s). Last edit at 11/02/2010 01:10PM by Buback.

Running the glass bead around the middle of the tub will take a little practice, but once perfected would make the strongest connection. You could even put springs on the vertical bolts to handle thermal expansion. The second approach should work, and will likely work better with roughed up edges for the ferrul to grip. On the other hand, the flange at the end is easier, I just need to work on getting it straight and even. And that should be the strongest.

PTFE washers are inexpensive from mcmasters. The larger outside diameter would fit well against the flanged end. I will see if I can get you one of each to experiment with.

Mike

yes i forgot to mention that the flanged nozzle is my preferred choice. it should be the strongest and simplest of the metal nozzle designs.

I also want to post about the cold end attachment i'm using.
Wade's has a 16mm diameter by 10 mm tall cavity in the bottom, where the filament exits the extruder. I filled this cavity with leftover M8 washers. (I don't know if they are standardized at 16mm OD, but mine were)


The glass tube is 8mm and fits perfectly in the washers, centered on the filament exit.


I cut a strip of aluminum to fit on the bottom of the wade's, and drilled holes to match the screw holes. I drilled a 8mm hole to match the, now 8mm, cavity. I did this by using a piece of masking tape as a template; stick the tape to the bottom of the extruder, poke a pen through the tape where the mounting screws go the mark the edges of the cavity, unstick, and match the mounting holes to the holes in the aluminum. I then used a large countersink bit i happen to have to make the M8 hole conical.


I made another ring to use as a ferrule on this end.


it's secure and looks great. it only adds 3mm to the height of the wade's
.


tightening it too much makes it bow a bit too much, could probably do with one less M8 washer. both the plastic and aluminum bow.

I currently have the mounting holes on the aluminum tapped for M4 screws. it's a bit annoying when attaching to the carriage, but helps keep everything tight until it is attached to the carriage. And you will need M4x20 screws; 16mm screws are just a bit too short and don't engage the captive nut.

very little heat moves up the tubing, but the aluminum and stack of washers should dissipate the heat that does.

Edited 2 time(s). Last edit at 11/03/2010 12:38PM by Buback.

I just happened onto this site, looking for info on embedding nichrome in borosilicate, and your pictures of the nozzles you made look a lot like the tips of the volumetric pipets I use at work. An 0.1 ml volumetric pipet from Corning or Kinble will have a very tiny, perfectly round hole in the tip. You'd just need to cut it off. You can often find these on eBay or at surplus sales. Some have tempered tips for extra strength.

Example: [compare.ebay.com]

Here's a useful wikipedia article on glass to metal seals. it's very informative.

Glass-to-metal seals

moon rabbit,
it looks like someone will need to acquire a few and see if the inside diameter is large enough for the 3 mm plastic filament to pass, or perhaps shift to the 1.8mm filaments. My sister works for a microscope stain and medical lab reagents house, and they might have some use once pipettes that she can pull for me to test after they have finished with them.


Mike

I adapted a wades extruder for mounting the glass nozzle to and attempted to print something, but it was pretty much a disaster. The heat traveled all the way up the glass nozzle and softened the carriage (which I only had fastened in one place anyway), this caused the (PLA) extruder to buckle and the print became quite inaccurate. I also noticed that whenever the extruder stopped for a while, it had trouble starting up again. I think this is because as the heat traveled up the glass is further while it was stopped, it softened more of the filament. Because the filament is not a snug fit, it expands when the extruder starts again rather than pushing more out the extrusion tip.

Having seen this, I think the top of the glass will need some form of cooling (aluminium housing and fins and a fan?)

Has anyone in the US been able to order the PTFE sleeving from McMaster discussed earlier in this thread that will go around the filament and inside the glass tube? That would help with the expansion of the filament and would also make it slide out easier. McMaster don't ship outside the US, so if someone can get some, I'd like to try it.



Edited 6 time(s). Last edit at 11/20/2010 10:54PM by Greg Frost.

Buback,
I have attempted to make to make the type of glass nozzles you requested. Some have a lip slightly up from the end so that two plates can sandwich the lip between them. Others have a flange at the end that I worked harder on getting perfectly flat and perpendicular. I also chucked several of them in the lathe and tried to square up the rounded edges and and make the addition more circular. As the photo bellow illustrates, this is not easy. If one of these designs should prove useful, I will have to work on improving the manufacture of that shape.

Greg,
I have no idea how the heat is getting up the glass. When I work the glass, the hot end is just at the edge of a dull red glow, and the other end I am usually holding in my hand. I can only guess that with time, the heat slowly makes its way up. That still means that very little heat energy is getting to the cold end, and it would not take much of a radiator to cool it. Perhaps try a brass grommet that will slide over the glass tube and crimp it just enough to be a tight fit. Or use the high temperature adhesive that I think Makershed sells.

ok rocketscientist: it took me a while, but I finally have one of the glass nozzles you sent me attached to an extruder.
I have a thin ptfe sleeving tube (thanks to Have Blue who kindly ordered it from mcmaster carr and posted it to Australia) whose OD almost perfectly matches the ID of the glass. This tube is pushed in all the way to the melt zone. It was too tight to push in until I lightly sanded it which prevented it from suctioning on to the glass. This tube both makes PLA easier to push through if it goes glassy and also takes up a bit of the slop (the ID was a bit big for 3mm filament). I now print with a fan blowing on the workpiece, so any heat that may have been convecting up the tube inside my carriage is now whisked away. I was able to make a successful print:

I observed you attempt to put the heater inside a capillary tube of glass. Looks interesting. How about simply making a section of your extruder out of the spiral rather than wrapping it around another glass. I think the guys that made the tips for the experimental glass tips would have the skill to do this quite well. I would expect that they could construct an extruder that was heated wrapped so that the wires came out in a convenient location and so that the heating was right at the tip. This is properly the job for a skilled glass operation. It would be 3 segments. 1 the upper segment is just glass tube with a proper entrance. The second segment is the heater spiral. The third segment is the tip that extrudes. I would think this could be made pretty strong and pretty good. If the top segment were made with a proper taper in it the risk of leaks into a PEEK mount is just about zero. I think you guys are onto something here.

I also suggest you look at ultrasonic heating because it can be applied right at the site of need and help fuse to the work piece allowing plastic extrusion in a true 6 axis application. --- This has real possibilities!