Should I fix my hot end or get a new one

I have a lathe and I am not afraid to use it! This pic is the Jhead that came with my MendelMax, and it had all of those scratches when it showed up. The threaded section was bent and it had been crossthreaded. I really wanted to root for this company I got it from because they made it so cheap, but now I know why. So the pathway is open over 3mm at the top and about 8mm in there is a lip that holds the PTFE sleeve from slideing up the heatsink. it Jams up regularly right at this bump, and it is kind of a no brainer that it shouldn't be there. So I am thinking of drilling it up and getting a longer PTFE tube to run the length of the jhead. Is the PTFE tube supposed to bottom out on the nozzle? Can it take that heat? Would I just be wasteing my time trying to get this piece of crap working, and I should just order a good Jhead? Do all jheads work in all printers or are there certain ones I should be looking at? What is the best kind?

ummm..... errr......

That's not a J Head.... That's some sort of all metal hot end. A J-Head has a black plastic body. There are a *lot* of all metal hot ends, not all of them work well. One might even say that most of them don't work well.

Sorry, but you'll have nothing but problems with that hotend, do yourself a favor and get a decent one. It's one of the most important parts in your machine! Not that you shouldn't shop around though.

If you have a lathe, do what you've said. It should work.
Drill through all the stainless tube. Put a long PTFE tube inside. Your maximum temperature is now 235°C, but you'll be able to print

Also, lathe the outer part of the threads, where we can see the outer threads from the outside at the minimum wall thickness you can achieve. Less section area -> less heat flux going up your hotend -> colder cold zone and less wasted energy.

There is a lot of voodoo in hot end design. The claimed magic (or lack there of) seems to involve:

1) The profile of heat as the filament goes down the tube (uniform in some / quite abrupt in others)
2) The taper of the tube in the (hopefully) melt zone. (none in many, "magic taper" in others)
3) Polish of the inner surface (PTFE all the way to what ever the drill left)
4) Heat sensing location (on the block / on the nozzle / close to the heater / far from the heater ...)
5) Liner / no liner
6) Mega heat sink (miles tall) / short heat sink / fat heat sink / skinny heat sink
7) Fan ducts
8) Subtle things like the diameter of the tube vs the filament diameter
9) Size of the nozzle (not just hole diameter)
10) Shape of the nozzle point

People spend a lot of time playing with all of this stuff. Some of the designs have been in the "we're still tweaking it" stage for years. Plastic is strange stuff, it's viscosity can change not just on the temperature, but also on the heating rate. It's not a simple liquid so modeling what's going on is not at all easy. Apparently getting all this stuff right is not at all easy.

Thanks for all the info, obviously I am new to this, I didn't realize that J-head was a specific one. If I had some PTFE tube I would just turn up the inside and use it, but I lost the little bit of extra that came with my printer, and the one in my hot end is messed up. Is that something I can find at a Home Depot or something? I am having trouble finding a place in the USA where I can find small printer parts like this, any suggestions? I can find some on Amazon, I was just hoping to get it today so I can get back to printing! I get that their is a lot of work that has gone into designing a hot end. I want to get a really good one (or make a copy of a really good one myself ;-{) what are the hot ends that you guys have had success with? Where could I buy them? is the J-head a really good one? What about Budaschnozzle?

Buy a real J-Head from the people who invented it. That way you are pretty sure it's not a clone and that there's someplace to go when you need this or that part for it.

Yes it costs more from them than from uncle_bob industries on eBay. Uncle_bob makes them out of old beer cans and isn't to careful with the machining details ....

[www.hotends.com]

I had similiar problems with a QU-BD mbe hot end. I spent a lot of time modifying it to get it to work. I drilled it out and added a ptfe liner but it still jammed. Best decision was when I binned it and got a jhead from hotends.com as recommended by uncle bob.
Mine was 0.4 nozzle and 1.75 filament size and is the Mk V version. It is a precision part. The machining is superb. I haven't looked back since. Coupled with a Gregs Wade extruder. All well sorted options. Ideal for ABS.

You can buy PTFE from McMaster-Carr.

If you have a lathe you could make a Budaschnozzle 2.0. I am in the process of making one myself. You will need to simplify the design on the mount plate if you don't have a CNC because of the arch. You will need a dividing head and a vertical mill to make some of the other parts.

The great thing about making a Budaschnozzle is that you can machine most of the parts from free scrap aluminum!

Take a look at:

1) A real J-Head

[www.hotends.com]

2) The E3D head

[e3d-online.com]

3) The Alu-Hotend

[3d-industries.myshopify.com]

All are in the $60 vicinity plus some shipping. Each of them has it's fans and it's not-so-fans. You should be able to get good performance out of any of them.

Nununugent:

where did you get the mendel max that the hotend came with ?

the reason that would be jamming is beause the stainless section is too short,

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thejollygrimreaper
Nununugent:

where did you get the mendel max that the hotend came with ?

the reason that would be jamming is beause the stainless section is too short,

Yes, very much so. I also have doubts about that aluminium "heat radiator".

I've used flat aluminium plates, look at the Eckertech design, it uses the same concept. You want to pull the heat away, not up along the filament feed path.

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Yvan

Singularity Machine

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Yvan

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thejollygrimreaper
Nununugent:

where did you get the mendel max that the hotend came with ?

the reason that would be jamming is beause the stainless section is too short,

Yes, very much so. I also have doubts about that aluminium "heat radiator".

I've used flat aluminium plates, look at the Eckertech design, it uses the same concept. You want to pull the heat away, not up along the filament feed path.

there's nothing wrong with the heatsink , it's being used in a way it wasn't designed and tested for, the stainless is supposed to be a minimum of 10mm between the heatsink and the heater block, in this case the thermal barrier is being used as a heat break which is just wrong

Edited 1 time(s). Last edit at 12/13/2013 04:51PM by thejollygrimreaper.

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Thanks for all the great advise! I got an origional j-head and I am getting it working now. I don't have any kapton tape and that is how he holds the thermistor in place. I jury-rigged a piece of wire to hold it in place and so far so good. Any other recommendations to hold it in place?

I got my MendelMax from Blomker industries. He is out of Malasia. For the size and capability it is great, and you couldn't beat the price. $700 for the I assembled kit, plus $100 S&H. The frame is very strong and he did a great job with the printed parts. The motors have had no problem. The board kept blowing the circuit breakers even though it was never drawing over 11.5 A. I replaced them both with 15 amp auto fuses at uncle bobs suggestion and have had no probs since. I got it thinking that it would have crappy parts and I would upgrade as I went, but I didn't realize how soon it would be.

Edited 1 time(s). Last edit at 12/14/2013 08:14PM by Nununugent.

Kapton tape is cheap enough (<$10 delivered) and it's easy to pull off. You may need to tear the hot end down.

I don't know enough about hot ends to understand what you mean by heat break and thermal barrier?

Yes, the gap is too short, but if there was a horizontal heat sink(where the base of the aluminium cylinder is now) wouldn't it have a better chance of drawing heat away from the filament coming along down the feed path? Right now it seems that the excessive heat reaching the cylindrical heat sink is more than enough to affect the filament on its way down.

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thejollygrimreaper

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Yvan

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thejollygrimreaper
Nununugent:

where did you get the mendel max that the hotend came with ?

the reason that would be jamming is beause the stainless section is too short,

Yes, very much so. I also have doubts about that aluminium "heat radiator".

I've used flat aluminium plates, look at the Eckertech design, it uses the same concept. You want to pull the heat away, not up along the filament feed path.

there's nothing wrong with the heatsink , it's being used in a way it wasn't designed and tested for, the stainless is supposed to be a minimum of 10mm between the heatsink and the heater block, in this case the thermal barrier is being used as a heat break which is just wrong

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Yvan

Singularity Machine

Nununugent, you meant the Blomker kit was unassembled, right?

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Yvan

Singularity Machine

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Yvan
I don't know enough about hot ends to understand what you mean by heat break and thermal barrier?

Yes, the gap is too short, but if there was a horizontal heat sink(where the base of the aluminium cylinder is now) wouldn't it have a better chance of drawing heat away from the filament coming along down the feed path? Right now it seems that the excessive heat reaching the cylindrical heat sink is more than enough to affect the filament on its way down.

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thejollygrimreaper

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Yvan

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thejollygrimreaper
Nununugent:

where did you get the mendel max that the hotend came with ?

the reason that would be jamming is beause the stainless section is too short,

Yes, very much so. I also have doubts about that aluminium "heat radiator".

I've used flat aluminium plates, look at the Eckertech design, it uses the same concept. You want to pull the heat away, not up along the filament feed path.

there's nothing wrong with the heatsink , it's being used in a way it wasn't designed and tested for, the stainless is supposed to be a minimum of 10mm between the heatsink and the heater block, in this case the thermal barrier is being used as a heat break which is just wrong

that would essentially be a "thermal break" and would require a much more aggressive heatsink,

in a thermal break: you separate the hot and cold section by a short thin section of stainless steel, the downside is you need to aggressively cool down and wick away all the heat energy that makes it across which is a considerable amount heat and is really just wasted energy and your firmware has to make sure your heater is putting out more energy to compensate for it, E3D Mk7 Mk7 up! extruders are examples of this , the good part of it is that the thermal barriers are easy to manufacture and the hotend as a whole can be made quite compact

in a thermal barrier : you separate the the hot and cold with a longer thin section of stainless, the way it works is that it takes quite a lot of heat energy to actually start heating the other end, from all the measurements i've taken on the tube there is a 100c drop just after the first 3mm and the heatsinks are cold to touch at anywhere between 25c and 35c the downside is there is a limit as to how short and compact you can make the hotend, the advantage is you are heating a hotend to then waste the heat again just for the sake of maintaining a temperature differential,


most hotend designs are built off the mk7 thermal break idea and a combination of thermal analysis modelling and don't in any instance consider the heat travelling up the filament in the modelling, where it can catch you out in a thermal break is that while the cold side may be getting maintained below the glass transition temperature of the plastic it doesn't nessessarily mean the plastic is actually under the same condition, what actually happens is that the filament is usually moving fast enough through the hotend the heat doesn't have a chance (kind of swims against the tide) of making its way past and up into the cold section.



what concerns me and why i asked where the kit came from is because the heat-sink looks suspiciously identical to mine and thats released under a NC license, the other thing is they shouldn't be advertising it in the kit as a jhead

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TJGR, I can't tell from your web site photos how much gap you have between the heater block and the heat sink, but it looks very close to what I used on mine. About 10 to 15 mm or so? That is the key element as you say. The Blomker varient can't possibly work well with the cylindrical style heat sink. All it does in that configuration is wick a lot of heat up towards the downward moving filament.

And yes, it is not a J-Head, in any way shape or form!

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Yvan

Singularity Machine

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thejollygrimreaper
what concerns me and why i asked where the kit came from is because the heat-sink looks suspiciously identical to mine and thats released under a NC license, the other thing is they shouldn't be advertising it in the kit as a jhead

Look at the MM 1.5 kit page on that Blomker site: [blomker.com]

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Blomker
All Metal Hot End (0.4mm nozzle diameter. 1.75mm filament)

But the MendelMax brochure.pdf that's linked in the same page does mention a J-head (with picture). Maybe Blomker used to sell their kits with J-heads and just switched to an all-metal one, and forgot to update the PDF?

The Assembly instructions are very nice. They do show a metal hotend, starting at page 77/108.

Hope you can straighten things out with them!

Edited 1 time(s). Last edit at 12/15/2013 04:10PM by NormandC.

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NormandC

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thejollygrimreaper
what concerns me and why i asked where the kit came from is because the heat-sink looks suspiciously identical to mine and thats released under a NC license, the other thing is they shouldn't be advertising it in the kit as a jhead

Look at the MM 1.5 kit page on that Blomker site: [blomker.com]

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Blomker
All Metal Hot End (0.4mm nozzle diameter. 1.75mm filament)

But the MendelMax brochure.pdf that's linked in the same page does mention a J-head (with picture). Maybe Blomker used to sell their kits with J-heads and just switched to an all-metal one, and forgot to update the PDF?

The Assembly instructions are very nice. They do show a metal hotend, starting at page 77/108.

Hope you can straighten things out with them!

i think you are right they just haven't gotten around to updating everything, my main reason i want to contact them is because i'm out of heatsinks and unless my cnc lathe is running inside the next week i might be out of stock until mid February so i might make them an offer for some of their stock

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Yes, I got a box of parts and put it together myself.

I am sorry if I caused any confusion, I can see from my writings earlier that it looked like I thought I had a real J-head. This just showed my ignorance. Blomker never said anything about a J-head, I just saw so many comments on J-heads that I thought all Hotends are J-heads. All my fault, don't blame him.

Edited 1 time(s). Last edit at 12/16/2013 09:20PM by Nununugent.