TG All metal Hot End - Call for help

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Re: TG All metal Hot End - Call for help

Postby LaserGnomes » Sat Jun 01, 2013 12:38 pm

TheTechGuru wrote:right around 1.69-1.7

What do you live in the high desert?!

The PLA comes out at 1.75mm that's the nozzle the manufacture is using. So for it to reduce size means it's lost content... and that could only be moisture.
We live 3 blocks from the pacific ocean at 10' above sea level. So our humidity reading is typically 45-55% all day every day year round.

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Re: TG All metal Hot End - Call for help

Postby Liquid » Sat Jun 01, 2013 12:43 pm

Im hoping so. I tried to keep both reverse feed and nozzle removal in mind when cleaning.

Worst case, you just unplug, unscrew the whole block, remove the clamping screw and pull the nozzle. Although Im going to have to add some flats to the stainless barrel for re-tightening of the block.

I would have made it so the nozzle just unscrews, but I wouldnt be able to use the clamping type method which I think will allow this design to stand out in performance. Like I said, its alllll theory at this point but Im not usually too far off when thinking these sorts of things out.

The quickest swap possible is ideal, but I think its worth the extra seconds.

This is why Im going for the mirror finish, I think its vital, and will ultimately give potential users an awesome experience, since that is the main goal next to being able to print everything within reach.

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Re: TG All metal Hot End - Call for help

Postby Liquid » Sat Jun 01, 2013 12:46 pm

What do you live in the high desert?!

HAHAHA, if you mean desolate.... is chicago close enough? lol

I bag all my pla after use, and stick the desiccant back in the center. Its prob a little swelled now because its been humid here the past few days, but I seriously get (pink for instance) 1.68x1.7 averaging 1.69 all around.

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Re: TG All metal Hot End - Call for help

Postby Liquid » Sat Jun 01, 2013 12:56 pm

There are three obvious step downs in diametere even on this "nozzle" cut away.

LG I honestly only see one step down before it hits the extrusion width.

I agree that it def needs the best taper possible, but just wanted you to take another look at this pic to see the barrel for the most part is just one straight shot. I think the taper where the barrel meets the nozzle is being mistaken for a taper in the filament chamber.


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Re: TG All metal Hot End - Call for help

Postby Liquid » Sat Jun 01, 2013 1:23 pm

Then go and read all the posts Nophead wrote about extruder design and thermal transition zones and all that.

Andrew, Found them. Some of the information is spread throughout the comments sections of different blog posts, but he links to them as he speaks which makes it easy to follow.

Reading them now, so far its been very interesting, Im already seeing that large transition zones may not work very well, and whats really needed is a really quick transition between hot and cold (less than 50c)

The question is.... what will my current design do??? I have to build it to find out even if it fails I think :)

So Im still reading, only 5 mins into it, if thats not the info you were referencing to, I will surely find it.

Im not exactly sure what the mk7 looks like internally, but Im guessing its missing a quick hot/cold transition zone, which causes the filament to soften/expand/drag at certain points while being pushed, resulting in jams. Esp if the filament stops moving for a period of time.

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Re: TG All metal Hot End - Call for help

Postby AndrewRutter » Sat Jun 01, 2013 1:44 pm


That's important stuff.

The Mk7's files should still be up on github, there are both solidworks files and pdf drawings of everything. Compare the design Nophead produced and the MBI one. Its 1 small detail that you need to add, and it sounds like you close to seeing it.

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Re: TG All metal Hot End - Call for help

Postby Liquid » Sat Jun 01, 2013 2:23 pm

Okay... lets see. I accessed the files on github, they might have taken a pdf schematic out (again Ive been up for a long period of time) Dont have the means to open solidworks just yet.

But let me take one last stab at it before I get some sleep, and revisit it later tonight. I really do want to figure this out on my own, I believe there is a learning process in there somewhere also. Ive only been printing for a month so my eye isnt as experienced as some in regards to hotends etc

One thing that stands out is that MBI didnt seem to incorporate the aluminum sleeve nophead used to draw heat away from the "cold end" of the barrel to the mounting plate.

I see that nopheads inner stainless barrel incorporated a reverse taper on the inside of the barrel towards the nozzle, Id have to take a guess that MBI didnt do this either.

I see he likes to use ptfe to enshroud the nozzle area, but thats mainly for cleanliness from what I can tell, insulating it, and keeping the consumables from sticking to the tip.

I also see he uses heatsink compound for joints... do hipsters use arctic silver? I would guess some sort of tea extract....

This is after needing sleep, and a virgin eye, but I have to say its the aluminum shroud/tube that carries heat away from the barrel to the mounting plate. If its any of those mentioned, that one seems the most important, right above the reverse tapered barrel ID, if that actually has an affect.

If its not any of those, leave it for me, Im going to read up on it when I wake up, I want the knowledge that comes with being able to spot it quickly for future references.

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Re: TG All metal Hot End - Call for help

Postby Liquid » Sun Jun 02, 2013 4:39 am

Andrew, so far I have arrived at this post on HydraRaptor ... ruder.html

Where at the end he summarizes the following:

For an extruder to work I think the transition zone needs at least two of the following three attributes: short, slippery or tapered.

Ive had a bit of much needed rest, after revisiting the previous post, I still think MBI left out the much needed aluminum outer shroud/tube type of element. Ive never used a makerbot, but my guess is that some of the jamming is due to the consumables expanding causing resistance. Maybe even some sort of backflow issue. If thats not it, its got to be the reverse taper (draft angle).

This new post (plumbstruder) has got me thinking, I either need to break up the central barrel of my design (from the top down) into a Stainless Top Insert, Stainless Bottom Barrel with the heatsink being drilled at both ends leaving a center core section of aluminum for the two stainless pieces mentioned above to butt up against.


Reverse Taper (Draft Angle) the internal dimension of the barrel. Both configurations still requiring a somewhat mirror finish I was originally intending.

Link of interest: ... raft-angle

But the one thing I cant get my mind wrapped around is the new prusa hotend, or the pico for that matter. They seem to be for the most part, just one singular material. One not having a heatsink of any sort, unless you count the mounting plate that is recommended, one having a heatsink using one of the worst materials for dissipating heat?

I mean... if these actually work, it "almost" (but not quite) negates any tests done, hotend related on HydraRaptors blog. Which I dont think is the case frankly. My suspicion is that these newer hotends either work, in which case Im going to study a similar design so see exactly why, or they both eventually "soak" at some point with heat, which is not good. Im guessing they soak with heat, and will cause problems eventually.

So.. as a builder/someone who likes to tinker yourself... you know how this type of thing goes. I just gotta dive right in... Obtain my own potential variables. Develop my own understanding of those variables based on what "I" see.

If you could pm me, or post your specific initial thoughts on my design, I would greatly appreciate it. Im not looking for any pulled punches here, I will take it all. It may very well help me at some point while Im dicking around with this.
Last edited by Liquid on Sun Jun 02, 2013 8:42 am, edited 1 time in total.

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Re: TG All metal Hot End - Call for help

Postby Liquid » Sun Jun 02, 2013 7:01 am

Ok, after a little more thought...

Im convinced the MBI mk7 barrel ID is missing the reverse taper (Draft Angle) where the barrel meets the nozzle firstly.

Secondly, coupled with an ultra smooth ID, should give good results.

And an aluminum barrel shroud towards the top end couldnt hurt.

Will know more once something is physically made and tested..

Thats my final conclusion I believe until I actually make something....
Last edited by Liquid on Sun Jun 02, 2013 7:10 am, edited 1 time in total.

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Re: TG All metal Hot End - Call for help

Postby Cohbra11 » Sun Jun 02, 2013 7:09 am

While I am definitely not claiming to be an expert on the subject matter here, I do have some experience with the design of flow testing systems including work that was awarded both international & US patents for a fully automated catalytic convertor core flow testing system,(unfortunately, I wasn't mentioned in the patents though).

With your design that has a taper going all the way down to the tip of the nozzle, I think you will have a lot of problems getting the print results that we all desire. You need a straight section without any taper at the tip of the nozzle in order to allow the melted plastic to establish laminar flow before it is extruded. Without it, the plastic will most likely want to curl in random directions as it exits the nozzle, just as if it were clogged. The longer the straight section, the better it will be for laminar flow. If I remember correctly, I think a length of 2.5-3 times the diameter is typically the minimum (it's been over 10 years so cut me some slack if I'm wrong there). Also, all transitions from one diameter to another should be as smooth and as gradual as possible. This will also improve laminar flow and make cleaning easier.

I would also recommend reducing the mass as much as possible in the elements that are heated which will reduce the amount of time required to raise or lower the temperature. However, I'm suspecting that a well tuned PID will be much more critical if the mass is considerably reduced.

I think I read somewhere earlier in this thread that someone mentioned reducing the size of the reservoir prior to the nozzle tip. This is something that I don't really have much of an opinion on, but I think there are a few things to consider that this reservoir will affect, only testing, I believe, will allow you to determine what is optimal. If the reservoir is too small (or nonexistent), then you might notice pulses in the extruded material due to the steps in the filament feed stepper (I haven't even been able to set eyes on my printer yet, so I may change my mind on this one after seeing it in action). However, if it is too large, you're increasing the amount of time that the filament sits, melted, waiting to reach the end of the nozzle for it's chance to be extruded. From what I've read, it sounds like this will lead to more hardened chunks building up over time and increasing the amount of cleanings necessary. Plus, due to the slightly compressible nature of plastic when it's melted, you will have more trouble with oozing when you stop feeding filament into the head as well as decreasing the responsiveness of the starting/stopping of the extrusion. I would personally start with the reservoir being as small as possible to see if the pulsing from the steps in the motor are even noticeable at all. If they are, then gradually increase the size of the reservoir just enough for them to disappear.

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