Prusa Nozzle MKII

my j-head nozzle broke so i though an upgrade to the Prusa nozzle MKII would be great. Or not?
I have been trying to print hole day but the filament keeps jamming.
I am printing PLA at 220-240 degrees have two fans cooling the heatsink.... still jamming...

anyone here having successful prints with PLA and prusa nozzle? I am really frustrated.

Hello,

What is broken on the J-Head? If everything appears to be ok, physically, try heating it up and tightening the hollow set-screw at the top end. It should take a 4mm hex key.

Regards,

Brian


thej Wrote:
-------------------------------------------------------
> my j-head nozzle broke so i though an upgrade to
> the Prusa nozzle MKII would be great. Or not?
> I have been trying to print hole day but the
> filament keeps jamming.
> I am printing PLA at 220-240 degrees have two fans
> cooling the heatsink.... still jamming...
>
> anyone here having successful prints with PLA and
> prusa nozzle? I am really frustrated.

well, when we look evolution of prusa nozzle looks like nozzle evolutes to the e3d hotend. it stil mmisses better heat conduit material in the nozzle

redirect the fans to only blow at the top 3 or 4 heat spreaders. with the fan exposed to the entire surface there is little change to the temp of the entire mechanism, top and bottom pretty much will equilize and nozzle heater will be on all the time. this allows for temps to rise up the hot end into the cold region, leaving the entire nozzle as a glass transition region. pla turns rubbery when it is in glass transition, and will grip about anything. you really want to keep the glass transition stage near the nozzle only in this design. or give abs a try.

I have tried everything its gets jammed ALL THE TIME i want to trow the nozzle in the garbage ffs.
80 euros of nozzle and you cant print PLA WELL DONE!

PLA is hard to print because of the very low glass transition temperature. You need to keep the top of the hotend below 58C or it will jam). You need to duct the airflow from that fan so that it only cools the heatsink part of the hotend.

i did. Nothing changed.

Hello,

Where did you get the J-Head? Was it from hotends.com or somewhere else?

Regards,

Brian



thej Wrote:
-------------------------------------------------------
> i did. Nothing changed.

Its the prusa nozzle mkII [reprapsource.com]
I dont like it this far...

Ok, now I understand. I thought you were having problems with the J-Head. (If the J-Head broke, it can be fixed.) You had a J-Head, it broke, and now you are having printing problems with the Prusa Mk II.

Regards,

Brian



thej Wrote:
-------------------------------------------------------
> Its the prusa nozzle mkII [reprapsource.com]
>
> I dont like it this far...

Maybe you could try putting a fan setup on it similar to the E3D one. It directly only cools the top several fins but they all stay cool to the touch. I can print PLA consistantly without jamming. I never even tried ABS yet.

You should be printing PLA at 195 with the Prusa V2 nozzle, not at 220-240, that's really way too hot for any hot-end. PLA starts to breakdown after 220.

Have you calibrated your thermistor, so you know the temperature is correct?

Have you limited the power to the hot-end PID? (use 160 rather than 255)

Have you ran an auto-tune M303 command to get the firmware settings for your hot-end.

It should work fine, I have been running a V2 with PLA for over a month now, no problems at all.

Or if you can't get on with fix your J-head, they are almost indestructible and can usually be fixed.

---

[richrap.blogspot.com]

Just throw it away and buy an E3D...

richrap Wrote:
-------------------------------------------------------
> You should be printing PLA at 195 with the Prusa
> V2 nozzle, not at 220-240, that's really way too
> hot for any hot-end. PLA starts to breakdown after
> 220.

Somehow Makerbot's default and recommended temp for a Replicator 2 is 230°C. And their parts curl up off the printbed. They have to superheat the PLA to make up for a bad extruder design and a bad printbed design. I run PLA anywhere from 185 to 200° depending on speed, layer height, and layer to layer print time with very good results.

Still no success with PLA ..... sucks.....
ABS prints just fine

Hey.

Your not the only one with these trouble, mine keeps jamming while printing ABS, I dont know if i have to much cooling on since my fan is ziptied to the top of the hotend.

Beekeeper Wrote:
-------------------------------------------------------

> Somehow Makerbot's default and recommended temp
> for a Replicator 2 is 230°C. And their parts curl
> up off the printbed. They have to superheat the
> PLA to make up for a bad extruder design and a bad
> printbed design. I run PLA anywhere from 185 to
> 200° depending on speed, layer height, and layer
> to layer print time with very good results.


I too can print PLA with a PTFE lined hotend at about 185 using a JHead or Aluhotend v4. The deal with an all metal hot end like the Prusa is that the thermal conductiivity of the material is less so it has to be heated more than brass or copper. With my Prusa v1 I had to go about the same as Rich suggests and even then PLA is dodgy after an hour so so due to heat travel up the material causing it to expand and jam. ABS @ 240*C works for hours on end. The primary advantage to an all metal hot end is being able to print at higher tenps for nylon, PVA, etc. Unless one needs those higher temps a lined hotend like an Aluhead or JHead I think is a better choice particularly if someone is new to printing and isn't experienced in machine setup.

make fan housing like e3d has, and problem solved....maybe....

woo Wrote:
-------------------------------------------------------
> make fan housing like e3d has, and problem
> solved....maybe....


With PLA the issue is heat traveling up the material due to the lack of a thermal insulator and the design of the transition zone. This issue was discussed pretty extensively when the first version came out (and in Sanjay's thread re: the E3D) but in a nutshell the fan can cool the hot end but it can't insulate the material internally like a liner can.

Edited 1 time(s). Last edit at 10/04/2013 03:05PM by vegasloki.

try oil on sponge wrapped around filament it has been mentioned in other threads. i tried everything with a similar hotend and was ready to give up tried this and not plugged since. i used vegetable oil.

You need to make sure that the fans are NOT blowing over the transition zone (short SS constriction between the heat block and the heat sink). It is essential that there is some sort of transition zone or else you may end up pulling liquid plastic into the "cold-side" on retractions. When this happens, the liquid plastic will cool in the cold side and form a plug and therefore jamming the hot end when your printer attempts to extrude again. A printed fan duct may be the way to go (as seen on the E3D hot end).

Eric

I found with my Prusa MK1 (and E3D at times)

If you leave the hotend idle with filament in it your gonna have a bad time and get jams

I normally let mine cool then start the prints so it starts printing as soon as its to temp so no idling.

iv not got a prusa Mk2 yet still waiting to hear from prusa but his on travels atm so not spoken with him

no jamming with mine e3d, and i actually dont have any problem with it, it cant be jammed, and i dont know how to do that, it just prints and prints...i have countless time set to preheat, ant then forgotten about it, left for hours etc....

Quote
thej
my j-head nozzle broke so i though an upgrade to the Prusa nozzle MKII would be great. Or not?
I have been trying to print hole day but the filament keeps jamming.
I am printing PLA at 220-240 degrees have two fans cooling the heatsink.... still jamming...

anyone here having successful prints with PLA and prusa nozzle? I am really frustrated.

Hi...
Have same problem with prusa nozzle MK II and I think I finally figured out whats causing it. Cause I have J-Head too it was easy to make some comparisions.
After countless of jamming/dismantle/cleaning for Prusa Nozzle I think I finally figured out whats causing the jam's.

Now look the attached photo.
There will be 2mm gap when everything is put together. For J-Head this ain't a problem cause that part is made of plastic, but for prusa nozzle this is big problem cause it's made from metal.
Heat accumulates on the 2mm gap and one point it will start slowly slicing filament with its edge and creates jam.

So from my research I conclude removing the gap should neutralize the jamming problems. Gona get back to confirm this when I get my J-Head up and running again and making new mount without the gap.

No luck at all with this nozzle (MKII, 3mm ABS) Always stuck! Looking forward to the findings (and maybe solution) of snowfly!

Quote
Snowfly

Quote
thej
my j-head nozzle broke so i though an upgrade to the Prusa nozzle MKII would be great. Or not?
I have been trying to print hole day but the filament keeps jamming.
I am printing PLA at 220-240 degrees have two fans cooling the heatsink.... still jamming...

anyone here having successful prints with PLA and prusa nozzle? I am really frustrated.

Hi...
Have same problem with prusa nozzle MK II and I think I finally figured out whats causing it. Cause I have J-Head too it was easy to make some comparisions.
After countless of jamming/dismantle/cleaning for Prusa Nozzle I think I finally figured out whats causing the jam's.

Now look the attached photo.
There will be 2mm gap when everything is put together. For J-Head this ain't a problem cause that part is made of plastic, but for prusa nozzle this is big problem cause it's made from metal.
Heat accumulates on the 2mm gap and one point it will start slowly slicing filament with its edge and creates jam.

So from my research I conclude removing the gap should neutralize the jamming problems. Gona get back to confirm this when I get my J-Head up and running again and making new mount without the gap.

That is the cold end, that gap should have no effect on jamming. The heat that melts the filament should be limited to the transition zone which is the gap between the heater block and the fins. If you are getting hot filament all the way up at the top of the hotend you have other issues.

Another thing to mention, I can print PLA (from JustPLA) at 170-175 with both the Budaschnozzle hotend and the E3D. You also never mentioned what kind of extruder. I tried designing my own direct drive to work with the E3D and it was jamming from 165-220, I went back to Wades and I am printing at 170.

Lastly, all-metal hotends were not made to print PLA. They are coming around now and becoming popular because of the availability of "exotic" materials like Polycarbonate, Nylon, and stuff like NinjaFlex which require temperatures that the PEEK hotends or PTFE liners can not take. People are using them with PLA because who wants to change hotends all the time?

If you are not intending to print materials that extrude at 240C+, you should have stuck with the typical PEEK body/PTFE lined hotends which are very reliable with PLA especially for newer users.

Edited 2 time(s). Last edit at 12/17/2013 01:06PM by tjb1.

Isn't it rather evident why the Prusa design is so prone to jams? Seems rather apparent to me...?

---

Yvan

Singularity Machine

Quote
Yvan
Isn't it rather evident why the Prusa design is so prone to jams? Seems rather apparent to me...?

That is definitely the case with the Prusanozzle MKI due to the very long and uncontrolled transition zone. However, Prusa added a heat sink to the MKII design and reduced the transition zone significantly, so from the theoretical perspective I would assume that it would work fairly reliably for ABS. Also, I think Jo Prusa polishes the inside of the SS Nozzle very well so theoretically PLA shouldn't be a problem either.

I am not sure why people are still having issues

Eric

Hey Eric, how are your projects going?

The Pico guys on Kickstarter have a nice thermal map of their hot end. In my mind is shows how things should be, heat flow wise. For that general style or layout anyways.

I should add the Pico heat zone is very long, so we will see how that works out in the real world.

Edited 1 time(s). Last edit at 12/17/2013 03:15PM by Yvan.

---

Yvan

Singularity Machine

Quote
Yvan
Hey Eric, how are your projects going?

The Pico guys on Kickstarter have a nice thermal map of their hot end. In my mind is shows how things should be, heat flow wise. For that general style or layout anyways.

I should add the Pico heat zone is very long, so we will see how that works out in the real world.

Yvan:

Unfortunately, life has been getting in the way and my projects have been moving along very slowly. However, things are clearing up and I am just about to start testing my final hot end prototype

I checked out the Pico Hot End on Kickstarter and it looks quite nice. However, I have to disagree with some of their design decisions, namely the use of Stainless Steel for the Heat Block and Heat Sink. While the 1 piece SS part simplifies the design, is mechanically strong, and looks pretty, it's thermal properties are not ideal for it's intended use. If you look at the E3D Hot End, there is a reason why Sanjay has a SS thermal break, but an Aluminium heat sink and heat block. You want the heat block temperature to be consistent so aluminium is ideal. The SS thermal break is effective in preventing heat transfer between the heat block and heat sink. The purpose of the heat sink is to disperse any heat that is transferred though the thermal break, so once again aluminium is ideal. The result of this design is a very short thermal transition from cool to molten plastic.

If you look at their thermal simulation, you can see that their hot end does not have a sharp thermal transition. From the picture I would estimate that the temp changes from 260C to about 45C (transition zone) over a length of about 30mm! This is very very long for a transition zone (It is 2mm in the E3D Hot End) This long transition zone was the cause of the jamming problems people were having with the original Prusanozzle MKI so theoretically I would assume that Pico would encounter the same issues.

They say that they have it working so my theoretical assumptions could be off... I hope I am wrong about these problems. It looks like they already have a lot of people backing this project and I wouldn't want the developers to get burned like Jo Prusa did when everyone started reporting problems with his Prusanozzle.

BTW, Yvan, how are your projects coming along? Have you been working on your Nylon printer?

Eric