The world's lightest open-source hot-end for 3mm?

Hello,

Based off of the J-Head nozzle , I may have the lightest 3mm hot-end at 14.7 grams. This weight includes the nozzle, nozzle holder, PTFE liner, hollow set-screw, heater resistor, and thermistor. While it is untested, I think the biggest unknown is how well the aluminum nozzle will work as the brass J-Head nozzles work quite well. (The aluminum is 2024, a lot harder and more expensive than the soft, gummy, hardware store aluminum that is quite common.)



Unfortunately, it is quite time-consuming to cut the flutes; but, if it works I may have it as an option. The fluting may also help to bleed off a lot of the heat. In the worst case, making this has helped me figure out how to lighten a more-feasible design.

It could probably be made lighter by:
1. Using a 6.8 ohm resistor and re-designing the nozzle around it. (Using this resistor would save 0.4 grams.)
2. Drilling lightening holes in the cold-end of the nozzle holder in the mounting groove area.
3. Using the 36.5 mm thermal barrier and making the same changes to it. (On some machines, it is too short.)

Given that the nozzle itself weighs under 4 grams, my guess is that a re-design could save 1 gram. It may be possible to reach 12 grams; but, I don't think it could be much lighter.

Regards,

Brian

Edited 6 time(s). Last edit at 08/21/2011 10:19PM by reifsnyderb.

That is a very nice looking hot end!

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That is one nice looking Hot End!

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Charles Gantt.
Build blog [themakersworkbench.com] <---- my personal site
Build worklong [www.thebestcasescenario.com]

While you're redesigning the nozzle, consider getting rid of the nipple. I find it easier to clean if there is no ridges from the edge of the nozzle all the way to the hole.

You won't get a flat top surface if you do that. The nozzle squashes the filament making it wider than the hole it comes out of. The nozzle needs to be flat out to that distance before it tapers away.

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[www.hydraraptor.blogspot.com]

Thanks everyone!

I just got in some 6.8 ohm resistors and there OD is smaller than expected. As a result, making a smaller nozzle may be more desirable as I could get the entire heater block into an area less than 13 x 13mm. So, I could make the nozzles with smaller stock.

I am going to look into it.

Regards,

Brian

If you got the Vishay ones from Farnel or Mouser they do seem smaller than the ones that Nophead used. I was surprised how small they were.

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Charles Gantt.
Build blog [themakersworkbench.com] <---- my personal site
Build worklong [www.thebestcasescenario.com]

Hello,

I got the Vishay ones from Digi-Key. The part number is RWMA-6.8CT-ND. I think mouser had them too. They are rated at 6.8 ohm, 3 watts.

In order to fit everything in a 13x13mm foot print, I'll have to leave the last 0.250 (or less) unsleeved and drill the remainder out to 3.5mm. I don't think that will be a problem as it will create a "heat chamber" of sorts. Besides, other designs have much longer sections unsleeved and the Universal Mini Extruder has a heat chamber like that as well. The resistor will be tucked right against the heat chamber. As a bonus, I think there will be room to put some 0-80 set screws in place to hold in both the resistor and thermistor. If this works, fire cement could be a thing of the past. I can also reduce the tapered area on the tip of the nozzle by a little bit. This design should be a nice, tight package and I am looking forward to machining it.

Who knows, it might even reduce the overall weight by another 0.5 grams.

Regards,

Brian






SCphotog Wrote:
-------------------------------------------------------
> If you got the Vishay ones from Farnel or Mouser
> they do seem smaller than the ones that Nophead
> used. I was surprised how small they were.

Quote

they do seem smaller than the ones that Nophead used

No they are exactly what I use. I did try some bigger ones initially but soon moved to those: [hydraraptor.blogspot.com]

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[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> You won't get a flat top surface if you do that.
> The nozzle squashes the filament making it wider
> than the hole it comes out of. The nozzle needs to
> be flat out to that distance before it tapers
> away.


ah, it can still have a flat tip (truncated cone), I'm just not a fan of the ridge.

Nice design. I would be interested in buying one when it's ready.

I don't think that the flute is necessary and it's probably not that efficient considering that the thermal conductivity of PEEK is low. A better way to cool it is to wrap it in aluminum or copper. For instance, two or more aluminum plates with four holes near each corner can be bent to ~170 deg arc and then bolted to the PEEK through the holes. You can also machine two heatsinks to do the same thing.

Thanks!

The main reason I fluted it was to reduce the weight. But, at the root of the flutes the PEEK is very thin. I would have to check my calculations; but, I think it is down to a little over 1/2mm. I do agree that the thermal conductivity of PEEK is very low. But, it could be enough to keep it cool. I don't really know. If it does keep it cool, it could completely eliminate the need for a separate heat-sink and that may be enough of a win to start fluting the nozzle holders.

On the other hand, I do have an aluminum heat-sink that sticks out either side of the PEEK nozzle holder. The heat-sink makes direct contact with the PTFE liner and has been proven to bleed off plenty of heat. While the aluminum heat-sink looks hard to make, once I have the right tooling it will be pretty easy. Since no hardware is required, installation only takes about 5 minutes. But the holes have to be drilled just right or things won't line up.

I may decide to make the Mk III with the aluminum heat-sink and either the aluminum nozzle or the smaller aluminum 6.8 ohm nozzle. Even with the heat-sink, it should be less than 21 grams. One of my big concerns is that the hot-end needs to be relatively quick to make. So, I have to keep in mind what I need to make it quickly.

Regards,

Brian





brnrd Wrote:
-------------------------------------------------------
> Nice design. I would be interested in buying one
> when it's ready.
>
> I don't think that the flute is necessary and it's
> probably not that efficient considering that the
> thermal conductivity of PEEK is low. A better way
> to cool it is to wrap it in aluminum or copper.
> For instance, two or more aluminum plates with
> four holes near each corner can be bent to ~170
> deg arc and then bolted to the PEEK through the
> holes. You can also machine two heatsinks to do
> the same thing.

Edited 2 time(s). Last edit at 08/24/2011 10:18PM by reifsnyderb.

Why not shorten the PEEK insulator and make the upper part out of aluminum with flutes?

Edited 1 time(s). Last edit at 08/24/2011 10:57PM by brnrd.

Hello,

The biggest reason is to keep the number of parts down. While aluminum is cheaper than PEEK, it is cheaper to have one expensive part as opposed to two cheaper ones. More parts also means more tooling, more time setting up machines (which is the most time-consuming part of making parts), and even more machines can be needed.

So, if possible, it would be ideal to have just a fancy PEEK nozzle holder as opposed to a PEEK nozzle holder and an aluminum heat sink.

The same goes for the nozzle. It is cheaper and easier (not to mention lighter and smaller), to have one nozzle/heater/thermistor mount as opposed to separate parts. This is even though the nozzle is rather complicated.

Regards,

Brian

brnrd Wrote:
-------------------------------------------------------
> Why not make the upper part of the thermal PEEK
> insulation out of aluminum?

reifsnyderb Wrote:
-------------------------------------------------------
> The same goes for the nozzle. It is cheaper and
> easier (not to mention lighter and smaller), to
> have one nozzle/heater/thermistor mount as opposed
> to separate parts. This is even though the nozzle
> is rather complicated.

I've found that one of the features I like most about MakerGear's "BigHead" design is that the head is easy to clean once it's removed from the heater. Given the troubles I've had with filament coking up the hot end, easy cleaning has become very important to me.

Hello,

I had a discussion, recently, with a J-Head nozzle user about cleaning. Since it is pretty easy to disassemble you can take it apart and clean everything. Optionally, it appears that acetone doesn't react with the PEEK, PTFE, the resistor, the thermistor, etc., so it may be possible to dip the whole thing in acetone. That idea needs some more testing, however. I don't know how fire cement will hold up, either.

In the end, though, the lack of modularity is a trade-off for a more light-weight and compact design.

Regards,

Brian




> I've found that one of the features I like most
> about MakerGear's "BigHead" design is that the
> head is easy to clean once it's removed from the
> heater. Given the troubles I've had with filament
> coking up the hot end, easy cleaning has become
> very important to me.

reifsnyderb Wrote:
-------------------------------------------------------
> doesn't react with the PEEK, PTFE, the resistor,
> the thermistor, etc., so it may be possible to dip
> the whole thing in acetone. That idea needs some
> more testing, however. I don't know how fire
> cement will hold up, either.

When ABS is heated above 260C, it starts to decompose and it becomes insoluble to acetone and probably most organic solvents. This happened to me a couple of times. I followed spacexula's repraplogphase video using a propane torch to burn off the insoluble ABS. This would require taking the hot end apart. I think nophead uses a drill by hand to clean the nozzle. This might be better so you don't have to take off the resistor and thermistor from the nozzle.

Thanks for the posting. Maybe drilling it is the way to go?

> When ABS is heated above 260C, it starts to
> decompose and it becomes insoluble to acetone and
> probably most organic solvents. This happened to
> me a couple of times. I followed spacexula's
> repraplogphase video using a propane torch to burn
> off the insoluble ABS. This would require taking
> the hot end apart. I think nophead uses a drill by
> hand to clean the nozzle. This might be better so
> you don't have to take off the resistor and
> thermistor from the nozzle.

Brian, Have you considered anodizing the aluminum? It should harden the surface considerably, and I expect it would make it easier to keep the nozzle clean.

While the aluminum, that I am using, is pretty hard that is a great idea as it would create a really hard surface coating! I never gave it a thought. The nozzle orifice be a problem...or not. But, we'll see how the aluminum works out first. If it does, then I'll investigate.

Thanks!

Brian


raldrich Wrote:
-------------------------------------------------------
> Brian, Have you considered anodizing the aluminum?
> It should harden the surface considerably, and I
> expect it would make it easier to keep the nozzle
> clean.

The extended nipple just means there is more length through which the plastic needs to be forced at the final nozzle opening diameter, and the extrusion force increases linearly in the length of this hole. You would be better off without the nipple (but still having the end slightly flattened). For the same reason, the larger diameter drilling inside of the nozzle should be drilled with a 'pointy bit' rather than a 'flat end' bit (whatever the jargon is), to help shorten the length of this narrow hole.

Hello,

The nozzle tip is at roughly the same angle as the drill bit in order to ensure that there is very little metal that the plastic must extruder through. However, I could probably shorten the spout a little more and will keep that in mind.

Thanks,

Brian



Lenbok Wrote:
-------------------------------------------------------
> The extended nipple just means there is more
> length through which the plastic needs to be
> forced at the final nozzle opening diameter, and
> the extrusion force increases linearly in the
> length of this hole. You would be better off
> without the nipple (but still having the end
> slightly flattened). For the same reason, the
> larger diameter drilling inside of the nozzle
> should be drilled with a 'pointy bit' rather than
> a 'flat end' bit (whatever the jargon is), to help
> shorten the length of this narrow hole.

Looking good Brian!

---

Charles Gantt.
Build blog [themakersworkbench.com] <---- my personal site
Build worklong [www.thebestcasescenario.com]

Anodizing aluminum can add more than .005" to the wall thickness of a part, and also may anodize unevenly inside the thin nozzle hole.

Just so you keep that in mind.



raldrich Wrote:
-------------------------------------------------------
> Brian, Have you considered anodizing the aluminum?
> It should harden the surface considerably, and I
> expect it would make it easier to keep the nozzle
> clean.

Hello,

That is a concern of mine, as well. The hole would need drilled after the part is anodized. Then, since the hole is really the most important section, as far as wear is concerned, the anodizing wouldn't help. It would look nice, though.

I wonder how well the anodizing would hold up with the heat, as well.

Regards,

Brian



Andrew Diehl Wrote:
-------------------------------------------------------
> Anodizing aluminum can add more than .005" to the
> wall thickness of a part, and also may anodize
> unevenly inside the thin nozzle hole.
>
> Just so you keep that in mind.
>
>
>
> raldrich Wrote:
> --------------------------------------------------
> -----
> > Brian, Have you considered anodizing the
> aluminum?
> > It should harden the surface considerably, and
> I
> > expect it would make it easier to keep the
> nozzle
> > clean.

Here is a pretty good handyman's reference for anodizing aluminum.

The value he gives for the size change is .0005", or 0.0127mm, which comes to around 4% of a .35mm hole - I don't think it would be noticeable in most printers. If Andrew's number is closer to correct, then it clearly would be an issue.

Heat, however, could be more of an issue - I found this discussion, which indicates that the anodized finish has a much lower coefficient of expansion than the aluminum. However, the temperatures they were discussing were in the 300c range, so it still might be worth the experiment.

Depends on the anodizing type and duration. My estimate was probably on the high side for normal applications.

My experience is with rocket motors casings, where coating thickness is a feature, not a bug :p