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made some progress on the next iteration of my metal hot end.
Added more cooling fins than before.
Changed overall shape. Machined from one solid piece of aluminum hexagon bar.
Filament tube is seamless stainless steel that will be formed on end to make the extrusion orifice.
My goal is to have seamless path for filament all the way from cold end to orifice.
Only two pieces for the complete hot end.
Still need to build tooling to form end of tube.

~*Brian

Wow! looks really nice Brian! Anxiously waiting for an "all metal" choice of hotend. This one looks like it will definitely be in the running.

ohhh when can i order one. been waiting for it.

bvandiepenbos wrote:Filament tube is seamless stainless steel that will be formed on end to make the extrusion orifice.
My goal is to have seamless path for filament all the way from cold end to orifice.

I understand the huge advantage of not having any seams, but stainless has relatively low thermal conductivity compared with aluminum, brass, or copper. That's why its used for a thermal break. Wouldn't that make it problematic to use for the nozzle orifice?

I don't think there is any issue using it for the nozzle orifice, if anything it should retain heat better. The prusa hotend is the same way.
I still think you'll have issues with PLA though, I can get decent prints in PLA out of the E3D Hotend, but it's considerably more sensitive to various settings and there is an issue with retraction, speculating as to what happens I would suggest that the rubbery PLA partially jams in the stainless tube on the forwards stroke dramatically increasing the time for the pressure to equalize, IME this leads to inconsistent extrusion following any significant retract.
Note with ABS and Nylon the E3D hotend is really very good.
I think Nopheads taper through the thermal break is probably the best solution to the issue, but for 1.75 it would probably require a custom tapered reamer.

Reading through the threads on the reprap forums about all metal hotends, some people seem to have some problems with all of them, and I have to wonder if any all metal hotend is the best choice for PLA.

I am now of the opinion it is not. While you can get it to work, the temperature window is so small and so sensitive it is simpler to just change to a jhead or the like and not have issues.

Thanks for all your helpful comments and suggestions!

Yes, I definitely want the I.D. of tubing to have a smooth taper to the orifice opening.
From 2mm to .35 mm in distance of 4mm is what I am shooting for.

If the filament can be kept well below it's softening point up to a short melt zone, I speculate the retract will work better.
Also hoping the smooth slow tapered I.D. at end will have less back pressure. Maybe even drool less, therefore needing shorter retracts.?

With my J-Head and ABS it seems to have better more predictable retracts with fan on hot-end ALL the time, keeping it really cool.
Could it be that the ABS is soft and stretchy some distance before the melt causing issues because it stretches thin on retract the balls/jams just a bit when restarting extrusion?
I do not *have* to run fan with ABS, but it works better I think.
PLA's lower melting point may just make it more of a problem than ABS/

~*Brian

Flateric wrote:I am now of the opinion it is not. While you can get it to work, the temperature window is so small and so sensitive it is simpler to just change to a jhead or the like and not have issues.

Flateric,
Do you think an all metal hot-end *IF* it's barrel is kept really cool could work as well as the J-Head with PLA?
Or are you thinking the slippery PTFE liner is why J-Head would be better for PLA?

~*Brian

bvandiepenbos wrote: PLA's lower melting point may just make it more of a problem than ABS/

~*Brian

No that's not the issue with PLA, it goes through another state between melted and solid where it has a rubbery consistency, the problem is in this state it expands outwards when pressure is applied and literally grips the wall of the extruder. This is the primary reason extruders moved to using PTFE liners.

Nopheads solution was the taper the Hotend through the transition zone, which is the same way that dies are made.

Polygonhell wrote:

bvandiepenbos wrote: PLA's lower melting point may just make it more of a problem than ABS/

~*Brian

No that's not the issue with PLA, it goes through another state between melted and solid where it has a rubbery consistency, the problem is in this state it expands outwards when pressure is applied and literally grips the wall of the extruder. This is the primary reason extruders moved to using PTFE liners.

Nopheads solution was the taper the Hotend through the transition zone, which is the same way that dies are made.

That helps to explain why the E3D has a problem with PLA.

Eaglezsoar wrote:
That helps to explain why the E3D has a problem with PLA.

I've gotten pretty good results with my replacement, even in PLA, but it's certainly not the easiest to use Hotend with PLA. I believe most of the issues come down to this.
They sort of get away with it because of the very short transition zone, which greatly reduces the need for retraction, and while printing at a reasonable speed results in a very short area where the PLA is in it's rubbery form. IME any significant retraction causes issues on the E3D with PLA, but you can just about get enough that kisslicers wipe will clean up the rest of the stringing.

I think the answer may just be two hotends, one for PLA and one for everything else and an easy way to swap between them.

Which is the BEST hot end for PLA?

g.

I think Jheads are hard to beat for PLA, there are a lot of them out there for good reason. I'd still run a fan on the peek, but for most of them you can get away without it.
They are not very friendly for higher temperature plastics, because the heater block literally screws into the peek, so destroying one by overheating it is very easy.
I also have a Budaschnozzle it's a good hotend, but very different, it requires very little pressure to extrude which results in the ability to print faster, but makes dealing with strings considerably more painful.

As a follow up to that, who makes the best j-head?

g.

Buy the original from hotends.com, you're supporting the creator and he's very quality conscious.

every time i go to that website there always out of stock.

From what I've been told, they're always out because a) they're that good and b) it's only one guy making them in his spare time.

g.

He does tend to go out of stock for weeks at a time.
It's one of the reasons I own a buddaschnozzle as well, at one point a year or so ago for several months a 1.75mm JHead might as well have been made of unobtanium.

If your going to buy a clone you should read this first, they're not all bad, but some of the generic Chinese copies don't bother to follow critical dimensions and are basically unusable.

http://jheadnozzle.blogspot.com/2012/12 ... lones.html

FWIW the same is true of some of the buddaschnozzle copies that have started to pop up.

yes, I agree the J-Head from hot-ends.com is the original and best. very nicely made. that is what I am currently running and it works great.
From what I hear he only takes orders on Fridays staring at Noon, then makes them for shipping out the following monday/tuesday.
That's what I did and got in the following thursday.

~*Brian V

Here is a revised design I machined up today for the cooling fins on my hot-end.
I think I will go with it. calling it the "Starfin" design
Test piece only has 2 fins, the actual one will be 1" long and have 5 fins of same dimensions.

~*Brian V

Is it just me or is the center hole WAY off?

g.

geneb wrote:Is it just me or is the center hole WAY off?

g.

Gene, I'm beginning to think that you are way off! I did get a chuckle out of it though!

Oh hell yes. I'm out of round too.

g.

bvandiepenbos wrote:Thanks for all your helpful comments and suggestions!

Yes, I definitely want the I.D. of tubing to have a smooth taper to the orifice opening.
From 2mm to .35 mm in distance of 4mm is what I am shooting for.

If the filament can be kept well below it's softening point up to a short melt zone, I speculate the retract will work better.
Also hoping the smooth slow tapered I.D. at end will have less back pressure. Maybe even drool less, therefore needing shorter retracts.?

With my J-Head and ABS it seems to have better more predictable retracts with fan on hot-end ALL the time, keeping it really cool.
Could it be that the ABS is soft and stretchy some distance before the melt causing issues because it stretches thin on retract the balls/jams just a bit when restarting extrusion?
I do not *have* to run fan with ABS, but it works better I think.
PLA's lower melting point may just make it more of a problem than ABS/

~*Brian

I am curious. How does one go about machining a smooth inner transition like the one you mention above? Grind down a nice sharp drill bit to have a pointy end?

When's this gonna be ready? I'm stuck using the stock hotend for PLA, hot-ends.com is out of stock, and I am dying to get this thing actually printing.