Prusa Nozzle MKII
Posted by thej
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Re: Prusa Nozzle MKII December 20, 2013 12:16AM |
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RP Iron Man
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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
Life? I think it does that to everyone!
I'm curious so see how the Pico hot end will do in the real world. The Pico is also shown at 260°C, well above typical. I think it is at the oposite end of the Prusa design, where the thermal break is not effective enough(too short), and too much heat is soaking up to the aluminium heat sink.
The nylon printer is on pause, I've been building a batch of Prusa i3s! I want to get back to the big machine though, I have all the parts for it now...
Yvan
Singularity Machine
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Re: Prusa Nozzle MKII December 20, 2013 12:34AM |
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Yvan
Life? I think it does that to everyone!
I'm curious so see how the Pico hot end will do in the real world. The Pico is also shown at 260°C, well above typical. I think it is at the oposite end of the Prusa design, where the thermal break is not effective enough(too short), and too much heat is soaking up to the aluminium heat sink.
The nylon printer is on pause, I've been building a batch of Prusa i3s! I want to get back to the big machine though, I have all the parts for it now...
Haha! Yeah, life can be a real PITA when you are trying to get stuff done.
Your points about the Pico hot end make sense. Having a longer thermal break really cuts down on the amount of active cooling that is required, but the trade-off is that the transition zone is also lengthened making the hot end more prone to jamming, especially with PLA. I imagine you could just throw a fan on the cold-side of the Pico when you are printing PLA to avoid this problem.
Perhaps the reason why people are having so much trouble with the Prusa MKII nozzle is because they are not using enough active cooling? The short thermal break necessitates a cooling fan on the heat sink. I would say that a 4CFM fan should be more than enough. I bottom part of the heat sink that is right above the thermal break should cool enough for you to touch without burning yourself!
Good luck with your Prusa I3 printers, Yvan! Let me know when you get that Nylon printer up an running. I'd be interested to see how it performs
Eric
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Re: Prusa Nozzle MKII December 20, 2013 01:01AM |
I appreciate your humor on some level, but I think you should be a little more diplomatic when you are making fun of people.
First of all, don't generalize. I did not buy the Prusanozzle MKI because I did not like the design (it was also rather expensive). Myself along with others on this forum noticed the lack of thermal control in the design and anticipated problems, of which there were many...
There will always be people who buy something because it looks cool or because it was "Designed by Jo Prusa", but to be fair to them, many do not understand the fundamentals of hot end design. So not everyone who bought the hot end is a "sheep". Some people just do not have the knowledge required to accurately judge the theoretical performance of a new design.
Also, many people here adopt a new design simply to help promote new development, which is a very good thing for RepRap. This helps fund the risk-takers and consequently helps us push the boundaries of what is possible within RepRap.
Next time you poke fun, do so in a way that is fair
Eric
First of all, don't generalize. I did not buy the Prusanozzle MKI because I did not like the design (it was also rather expensive). Myself along with others on this forum noticed the lack of thermal control in the design and anticipated problems, of which there were many...
There will always be people who buy something because it looks cool or because it was "Designed by Jo Prusa", but to be fair to them, many do not understand the fundamentals of hot end design. So not everyone who bought the hot end is a "sheep". Some people just do not have the knowledge required to accurately judge the theoretical performance of a new design.
Also, many people here adopt a new design simply to help promote new development, which is a very good thing for RepRap. This helps fund the risk-takers and consequently helps us push the boundaries of what is possible within RepRap.
Next time you poke fun, do so in a way that is fair
Eric
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Re: Prusa Nozzle MKII December 20, 2013 01:24AM |
That's a pretty good reaction. I can respect that too. 
I have seen your posts in threads all over the forum and I think people find that you are a little too extreme/unfair in your posts. I think if you took a more diplomatic approach people would have much more respect and would be more willing to listen to what you have to say. From what I've seen, you seem to have a fair bit of useful knowledge, so try not to just waste it on being ridiculous with people. I think people would enjoy having interesting discussions with you, but not if you are constantly trying to make fools of them.
Just my $0.02
Eric
I have seen your posts in threads all over the forum and I think people find that you are a little too extreme/unfair in your posts. I think if you took a more diplomatic approach people would have much more respect and would be more willing to listen to what you have to say. From what I've seen, you seem to have a fair bit of useful knowledge, so try not to just waste it on being ridiculous with people. I think people would enjoy having interesting discussions with you, but not if you are constantly trying to make fools of them.
Just my $0.02
Eric
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Re: Prusa Nozzle MKII December 20, 2013 01:43AM |
Don't be so didactic. That's my $0.02
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Re: Prusa Nozzle MKII December 20, 2013 02:05AM |
Haha! You were misbehaving, I thought you needed some schooling
Eric
Eric
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Re: Prusa Nozzle MKII December 22, 2013 09:41AM |
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RP Iron Man
Perhaps the reason why people are having so much trouble with the Prusa MKII nozzle is because they are not using enough active cooling? The short thermal break necessitates a cooling fan on the heat sink. I would say that a 4CFM fan should be more than enough. I bottom part of the heat sink that is right above the thermal break should cool enough for you to touch without burning yourself!
replaced the delivered fan with a larger one and still no luck at all! (ABS)
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Re: Prusa Nozzle MKII December 24, 2013 04:19PM |
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Frans@France
metric prusa i3, wade extruder, tried every extruder spring tension that was possible. eats filament
- printing at 220
- filament diameter is a bit weird! on one side very stable 2.97 but on it's other side it's flatter as flat as 2.91!
internal bore seems to be 3.05
Ok, if your measurements are correct, your filament should be able to pass through the 3.05mm internal bore. In addition, since the filament is very close to the bore diameter, you should have much less back-pressure during extrusion so it should not be difficult to feed the filament.
As an experiment, try pushing the filament through the hot end using your hand. You should be able to extrude the filament like this. If you can, then the problem is likely a result of a poor hobbed bolt, or insufficient spring tension. Could you attach a picture of your hobbed bolt and spring tension setup?
If you cannot extrude the filament by hand, then the problem is definitely the hot end. If this is the case, try feeding the filament down into the hot end and see if you encounter any resistance as the filament slides through the internal bore of the hot end. If the filament is the right size, you should encounter very little resistance. Also, it would be helpful if you could attach a pic of your setup because I actually do not have a Prusanozzle MKII so I am not exactly sure how the setup looks.
I hope this helps
Eric
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Re: Prusa Nozzle MKII December 24, 2013 05:44PM |
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RP Iron Man
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Yvan
SNIP>>>
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
Is there a 'thermal simulation' of the E3D to compare?
_______________________________________
Waitaki 3D Printer
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Re: Prusa Nozzle MKII December 24, 2013 05:52PM |
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RP Iron Man
Ok, if your measurements are correct, your filament should be able to pass through the 3.05mm internal bore. In addition, since the filament is very close to the bore diameter, you should have much less back-pressure during extrusion so it should not be difficult to feed the filament.
As an experiment, try pushing the filament through the hot end using your hand. You should be able to extrude the filament like this. If you can, then the problem is likely a result of a poor hobbed bolt, or insufficient spring tension. Could you attach a picture of your hobbed bolt and spring tension setup?
If you cannot extrude the filament by hand, then the problem is definitely the hot end. If this is the case, try feeding the filament down into the hot end and see if you encounter any resistance as the filament slides through the internal bore of the hot end. If the filament is the right size, you should encounter very little resistance. Also, it would be helpful if you could attach a pic of your setup because I actually do not have a Prusanozzle MKII so I am not exactly sure how the setup looks.
I hope this helps
Eric
Eric, thanks for the help, much appreciated!
Impossible to push the filament down by hand. It will hit the bottom of the hotend end that's it. I got the temp up to 300 and still no go! The filament will slide into the bore with minor (not consistent) resistance. On retract it will most of the time show a double melted tip of the filament with a long (very long) wisker. So wisker- solid filament 3-4 mm long then some thin (melted) and then again solid.
Will try to make some shots and post them, do have to install it again because currently running a j-head without any issue with the same filament @225
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Re: Prusa Nozzle MKII December 24, 2013 06:11PM |
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Frans@France
Eric, thanks for the help, much appreciated!
Impossible to push the filament down by hand. It will hit the bottom of the hotend end that's it. I got the temp up to 300 and still no go! The filament will slide into the bore with minor (not consistent) resistance. On retract it will most of the time show a double melted tip of the filament with a long (very long) wisker. So wisker- solid filament 3-4 mm long then some thin (melted) and then again solid.
Will try to make some shots and post them, do have to install it again because currently running a j-head without any issue with the same filament @225
Ok, definitely an issue with the hot end. It seems like the transition zone is uncontrolled and is very long, causing the resistance. A pic of the filament that you tried to push through the hot end would really help me get to the bottom of this
Eric
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Re: Prusa Nozzle MKII December 27, 2013 01:13AM |
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RP Iron Man
The Pico thermal simulation is more of a marketing facet than design verification.
Eric
Meh, not much of a surprise there, but I didn't know that. Will not be so gulible next time!
Yvan
Singularity Machine
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Re: Prusa Nozzle MKII December 27, 2013 01:27PM |
Regarding the E3D and thermal analysis of CAD - I've done a fair bit of this stuff a long time ago outside of the scope of 3D printing, and I did run plenty of analysis in the design/verification stages. However I am also aware of when these types of techniques fail to produce useful results - this is very much one of them.
The real design, analysis and calculation were done on a whiteboard with little more than fouriers thermal transfer equations, a bit of thermal resistance calculation and a hell of a lot of empirical analysis. I did do some post-facto analysis and sanity checking on CAD. I actually hoped I'd get some pretty thermal heat-map of temperature gradients in a beautiful rainbow like you see in the B3 blurb. Simple fact is that what I got was a heater-block, and nozzle that were uniformly scarlet red, and a heatsink that was uniformly blue. With a tiny little 2mm rainbow across the thin section of the heatbreak. It's not very interesting, nor does it provide any info beyond what I already knew.
Let us also bear in mind that the conditions we print in vary hugely, with print temperature ranging from 170C to 300C, and the temperature of the air we're pulling over the heatsink can be from 15C to over 75C in some cases. What do we stand to gain from computational analysis in a scenario with variables that range as wildly as this? Increased accuracy certainly isn't attainable because the data we would enter into our simulation would not be accurate for anything other than that single scenario.
The reasoning and design philosophy behind the E3D is simple; take these above hugely variable factors with dynamically changing variables, and with a fair bit of brute force engineering (big heatsink + fast fan, short sudden thermal break, high power heater cartridge) force the system to behave in an almost entirely static and predictable fashion where it remains in a state that works no matter what the user with a plethora of machines, materials and conditions throws at it.
The hot area where the plastic is liquid and flows remains hot, and of predictable length due to high conductivity of the block and nozzle, low heat creep up the break, and high power cartridge allows the PID to react to compensate for energy loss quickly.
The large heatsink with active cooling has only a small amount of heat flowing into it, which is rapidly removed by the fan. This maintains the filament within the heatsink as a rigid and effective plunger. It also ensures that the printed parts holding the hotend will not melt or deform.
The short heat break keeps the area of plastic in the undesirable state where it is semi-molten and adheres to the walls to an absolute minimum this prevents jamming and gives a consistent low extrusion force. This also maintains a consistent melt-zone length so you increase the volumetric precision of your extrusion. Imagine a PEEK hotend with a gradual transition, or indeed something like the Prusa nozzle - when extrusion is slow the melt-zone is long, there is a longer section of expanded filament in the bore, when extrusion is fast the melt-zone is short, there is less expanded filament in the bore. When you change from the slow state to the fast state you are effectively over-extruding as the melt-zone shifts downwards plunging out additional filament. The inverse happens in the change from fast to slow - you under extrude as the melt-zone increases in length consuming plastic that by your Slic3rs calculations should be being extruded. Obviously this is a simplified two-state thought experiment, and what actually happens in the hotend is more dynamic and complex as we change through a multitude of extrusion rates and accelerations. Nophead also documents this in his most recent blog post. By confining the shift in melt-zone length to around 2mm in the E3D this error is minimised.
TL;DR
Simulation is nice, reality is more reliable.
I Design/Sell all-metal hotends. My company is called e3d-online - you can buy at [www.e3d-online.com]
The real design, analysis and calculation were done on a whiteboard with little more than fouriers thermal transfer equations, a bit of thermal resistance calculation and a hell of a lot of empirical analysis. I did do some post-facto analysis and sanity checking on CAD. I actually hoped I'd get some pretty thermal heat-map of temperature gradients in a beautiful rainbow like you see in the B3 blurb. Simple fact is that what I got was a heater-block, and nozzle that were uniformly scarlet red, and a heatsink that was uniformly blue. With a tiny little 2mm rainbow across the thin section of the heatbreak. It's not very interesting, nor does it provide any info beyond what I already knew.
Let us also bear in mind that the conditions we print in vary hugely, with print temperature ranging from 170C to 300C, and the temperature of the air we're pulling over the heatsink can be from 15C to over 75C in some cases. What do we stand to gain from computational analysis in a scenario with variables that range as wildly as this? Increased accuracy certainly isn't attainable because the data we would enter into our simulation would not be accurate for anything other than that single scenario.
The reasoning and design philosophy behind the E3D is simple; take these above hugely variable factors with dynamically changing variables, and with a fair bit of brute force engineering (big heatsink + fast fan, short sudden thermal break, high power heater cartridge) force the system to behave in an almost entirely static and predictable fashion where it remains in a state that works no matter what the user with a plethora of machines, materials and conditions throws at it.
The hot area where the plastic is liquid and flows remains hot, and of predictable length due to high conductivity of the block and nozzle, low heat creep up the break, and high power cartridge allows the PID to react to compensate for energy loss quickly.
The large heatsink with active cooling has only a small amount of heat flowing into it, which is rapidly removed by the fan. This maintains the filament within the heatsink as a rigid and effective plunger. It also ensures that the printed parts holding the hotend will not melt or deform.
The short heat break keeps the area of plastic in the undesirable state where it is semi-molten and adheres to the walls to an absolute minimum this prevents jamming and gives a consistent low extrusion force. This also maintains a consistent melt-zone length so you increase the volumetric precision of your extrusion. Imagine a PEEK hotend with a gradual transition, or indeed something like the Prusa nozzle - when extrusion is slow the melt-zone is long, there is a longer section of expanded filament in the bore, when extrusion is fast the melt-zone is short, there is less expanded filament in the bore. When you change from the slow state to the fast state you are effectively over-extruding as the melt-zone shifts downwards plunging out additional filament. The inverse happens in the change from fast to slow - you under extrude as the melt-zone increases in length consuming plastic that by your Slic3rs calculations should be being extruded. Obviously this is a simplified two-state thought experiment, and what actually happens in the hotend is more dynamic and complex as we change through a multitude of extrusion rates and accelerations. Nophead also documents this in his most recent blog post. By confining the shift in melt-zone length to around 2mm in the E3D this error is minimised.
TL;DR
Simulation is nice, reality is more reliable.
I Design/Sell all-metal hotends. My company is called e3d-online - you can buy at [www.e3d-online.com]
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Re: Prusa Nozzle MKII December 27, 2013 01:54PM |
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Yvan
Meh, not much of a surprise there, but I didn't know that. Will not be so gulible next time!
Yvan, you shouldn't blame yourself. I am sure that the B3 guys have also done lots of empirical testing as well. I assume they included the thermal imaging as a way to establish some professional credibility with the Kickstarter crowd. While most people will be impressed by the fancy CAD simulations, it would have been much better if the B3 guys had simply attached a video of their Pico printing something. That and a few pictures of print quality would do much more to establish their credibility than a rather inaccurate thermal simulation.
Eric
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Re: Prusa Nozzle MKII December 27, 2013 02:01PM |
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SanjayM
Regarding the E3D and thermal analysis of CAD - I've done a fair bit of this stuff a long time ago outside of the scope of 3D printing, and I did run plenty of analysis in the design/verification stages. However I am also aware of when these types of techniques fail to produce useful results - this is very much one of them.
The real design, analysis and calculation were done on a whiteboard with little more than fouriers thermal transfer equations, a bit of thermal resistance calculation and a hell of a lot of empirical analysis. I did do some post-facto analysis and sanity checking on CAD. I actually hoped I'd get some pretty thermal heat-map of temperature gradients in a beautiful rainbow like you see in the B3 blurb. Simple fact is that what I got was a heater-block, and nozzle that were uniformly scarlet red, and a heatsink that was uniformly blue. With a tiny little 2mm rainbow across the thin section of the heatbreak. It's not very interesting, nor does it provide any info beyond what I already knew.
Let us also bear in mind that the conditions we print in vary hugely, with print temperature ranging from 170C to 300C, and the temperature of the air we're pulling over the heatsink can be from 15C to over 75C in some cases. What do we stand to gain from computational analysis in a scenario with variables that range as wildly as this? Increased accuracy certainly isn't attainable because the data we would enter into our simulation would not be accurate for anything other than that single scenario.
The reasoning and design philosophy behind the E3D is simple; take these above hugely variable factors with dynamically changing variables, and with a fair bit of brute force engineering (big heatsink + fast fan, short sudden thermal break, high power heater cartridge) force the system to behave in an almost entirely static and predictable fashion where it remains in a state that works no matter what the user with a plethora of machines, materials and conditions throws at it.
The hot area where the plastic is liquid and flows remains hot, and of predictable length due to high conductivity of the block and nozzle, low heat creep up the break, and high power cartridge allows the PID to react to compensate for energy loss quickly.
The large heatsink with active cooling has only a small amount of heat flowing into it, which is rapidly removed by the fan. This maintains the filament within the heatsink as a rigid and effective plunger. It also ensures that the printed parts holding the hotend will not melt or deform.
The short heat break keeps the area of plastic in the undesirable state where it is semi-molten and adheres to the walls to an absolute minimum this prevents jamming and gives a consistent low extrusion force. This also maintains a consistent melt-zone length so you increase the volumetric precision of your extrusion. Imagine a PEEK hotend with a gradual transition, or indeed something like the Prusa nozzle - when extrusion is slow the melt-zone is long, there is a longer section of expanded filament in the bore, when extrusion is fast the melt-zone is short, there is less expanded filament in the bore. When you change from the slow state to the fast state you are effectively over-extruding as the melt-zone shifts downwards plunging out additional filament. The inverse happens in the change from fast to slow - you under extrude as the melt-zone increases in length consuming plastic that by your Slic3rs calculations should be being extruded. Obviously this is a simplified two-state thought experiment, and what actually happens in the hotend is more dynamic and complex as we change through a multitude of extrusion rates and accelerations. Nophead also documents this in his most recent blog post. By confining the shift in melt-zone length to around 2mm in the E3D this error is minimised.
TL;DR
Simulation is nice, reality is more reliable.
Thanks for chiming in here Sanjay
I totally agree with your analysis of the hot end dynamics. It is the core of the success of your E3D hot end and all other successful all metal hot ends on the market. I am not sure of how the B3 Pico hot end will perform as they have not been very open about the real world performance, but I am very interested so see how it turns out.
It looks like they already have $36,000 in kickstarter funding!
Eric
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