Re: Prusa Nozzle MKII December 17, 2013 10:27PM |
Registered: 11 years ago Posts: 661 |
Re: Prusa Nozzle MKII December 18, 2013 05:12AM |
Registered: 11 years ago Posts: 528 |
Re: Prusa Nozzle MKII December 20, 2013 12:16AM |
Registered: 17 years ago Posts: 392 |
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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
Re: Prusa Nozzle MKII December 20, 2013 12:18AM |
Registered: 17 years ago Posts: 392 |
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vegasloki
After a fair amount of tinkering I've been able to get a Prusa v1 very reliable for 230* plus temp material. A bit of PID tuning, a fan and finding the minimum extrusion temps for the material and I was good to go. It took quite a bit of work to make it happen. No go for PLA but I have an Aluhead I can use that prints great pretty much out of the box with minimal tuning.
Anonymous User
Re: Prusa Nozzle MKII December 20, 2013 12:32AM |
Re: Prusa Nozzle MKII December 20, 2013 12:34AM |
Registered: 11 years ago Posts: 246 |
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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...
Re: Prusa Nozzle MKII December 20, 2013 12:36AM |
Registered: 11 years ago Posts: 246 |
Anonymous User
Re: Prusa Nozzle MKII December 20, 2013 12:42AM |
Re: Prusa Nozzle MKII December 20, 2013 01:01AM |
Registered: 11 years ago Posts: 246 |
Anonymous User
Re: Prusa Nozzle MKII December 20, 2013 01:11AM |
Re: Prusa Nozzle MKII December 20, 2013 01:24AM |
Registered: 11 years ago Posts: 246 |
Anonymous User
Re: Prusa Nozzle MKII December 20, 2013 01:43AM |
Re: Prusa Nozzle MKII December 20, 2013 02:05AM |
Registered: 11 years ago Posts: 246 |
Re: Prusa Nozzle MKII December 22, 2013 09:41AM |
Registered: 10 years ago Posts: 550 |
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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!
Re: Prusa Nozzle MKII December 22, 2013 01:42PM |
Registered: 11 years ago Posts: 246 |
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Frans@France
replaced the delivered fan with a larger one and still no luck at all! (ABS)
Re: Prusa Nozzle MKII December 24, 2013 01:01PM |
Registered: 10 years ago Posts: 550 |
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RP Iron Man
Could you post your printing specs for me?
- Filament diameter? If 3mm let me know if it measures 2.85 +/- 0.1 or if it is 3 +/- 0.1.
- Geared extruder?
- Printing temp?
- Adequate extruder spring tension?
Also could you post a pic of your setup so I can see what it looks like?
Re: Prusa Nozzle MKII December 24, 2013 04:19PM |
Registered: 11 years ago Posts: 246 |
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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
Re: Prusa Nozzle MKII December 24, 2013 05:44PM |
Registered: 11 years ago Posts: 1,592 |
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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 (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.
Is there a 'thermal simulation' of the E3D to compare?
_______________________________________
Waitaki 3D Printer
Re: Prusa Nozzle MKII December 24, 2013 05:52PM |
Registered: 10 years ago Posts: 550 |
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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
Re: Prusa Nozzle MKII December 24, 2013 06:05PM |
Registered: 11 years ago Posts: 246 |
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waitaki
Is there a 'thermal simulation' of the E3D to compare?
Re: Prusa Nozzle MKII December 24, 2013 06:11PM |
Registered: 11 years ago Posts: 246 |
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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
Re: Prusa Nozzle MKII December 27, 2013 01:13AM |
Registered: 17 years ago Posts: 392 |
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RP Iron Man
The Pico thermal simulation is more of a marketing facet than design verification.
Eric
Re: Prusa Nozzle MKII December 27, 2013 01:18AM |
Registered: 17 years ago Posts: 392 |
Re: Prusa Nozzle MKII December 27, 2013 01:27PM |
Registered: 12 years ago Posts: 177 |
Re: Prusa Nozzle MKII December 27, 2013 01:54PM |
Registered: 11 years ago Posts: 246 |
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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!
Re: Prusa Nozzle MKII December 27, 2013 02:01PM |
Registered: 11 years ago Posts: 246 |
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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.
Re: Prusa Nozzle MKII December 29, 2013 07:18PM |
Registered: 11 years ago Posts: 544 |
Anonymous User
Re: Prusa Nozzle MKII December 29, 2013 09:06PM |
Re: Prusa Nozzle MKII December 30, 2013 12:57AM |
Registered: 11 years ago Posts: 544 |
Re: Prusa Nozzle MKII December 30, 2013 02:00AM |
Registered: 10 years ago Posts: 52 |