Firmware speed extrusion multiplier = f(target extrusion rate)
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Interesting points vp, and you do sound as if you have some knowledge in this area. A couple of things I'd like to pick up on, as they seem contrary to my experience so far (which could be because I have been making wrong assumptions or not).
a) Transition zone, I am now using water cooling for my heatsink which is never above 28 deg C even in a heated chamber. I should expect to be able to extrude a higher volumetric rate of filament all other factors being equal?
b) Are you printing 300-400 mm/s with a 0.4mm nozzle? As above I ask as I have not managed to exceed 9.1mm3/s via volcano/0.4 without significant under-extrusion, although I have not tried "boosting" the extrusion multipler under these conditions. Although I did try increasing the temperature which had as you point out only minimal effect. (210 to 230 for PLA).
c) Have you seen or tried Prometheus hotend where you can alter the length of the melt zone? Are you suggesting that short with a sharp transition would yield best results?
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The empirical data that I have collected is at odds with your theories so we'll just have to disagree. I can't bring myself to believe that time in contact (with a hot surface) is not a consideration.
Oh, by the way what you say about the Diamond geometry is completely wrong. The 0.4mm section is only 3mm long for each filament and then there is a combined 2mm section so a maximum of 5mm which is about the same as a V6 and not multiple parts longer as you state. Of course, the diameter isn't always 0.4mm -mine are mostly 0.5mm but I also have a 0,9mm version.
Anyway, we won't dwell on that. You are obviously very enthusiastic about your theory. Personally I just can't buy into it.
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@ DjDemonD.
ad a. my understanding is, that when filaments get soft, they get "sticky" (especially PLA). The shorter the transition zone, the shorter is the "high" friction zone. Increasing cooling leads to a sharper/bigger temperature gradient, which will make the trans zone shorter - this is good. On the other handside, if your cold end cools e.g. 20 W more than usual, your hot end has to provide the power - beyond a certain point this might get tricky. But i would expect that your constant thermal extrusion capacity is increased when cooling more. With air i had never the problem that i did cool too much. What should not happen is, that your transition zone is shifted inside the hot end - which is possible (at least in theory).
When priniting PLA, PTFE inliners which go directly to the hot end (through the throat) also allows about the same speed as with a full metal titan throat. So i guess it is really about the friction in the transition zone.
ad b. I have 2 printers, a slow one with an e3d v6 setup and a fast one with the following hot end (ubis style).
https://www.aliexpress.com/store/product/E3D-Upgrade-parts/1654223_32697889176.html.
With e.g. extrdr MF PLA 240 °C i have no problem to extrude with a 0.5 mm e3d like nozzle 1.75 filament with 10 mm/s, this is about 24 mm³/s or equals at 0.6 mm layer width at 0.2 mm layer height and 200 mm/s. And this is just a "e3d v6" hot end - no volcano. But i cannot print that fast with e.g. retraction. Any disturbance of the "constant extrusion capacity" will give underextrusion. At top/bottom layers this is no big problem (no retraction).With a volcano nozzle and the same hot end (no long e3d heating block) i manage > 300 mm/s at same conditions. If i reduce the layer height to < 0.2mm e.g. 0.1 mm 400 mm/s are no problem.
ad c. i did/do combine a volcano nozzle with the above ubis style heaterblock - the heater block is not located towards the nozzle tip, it is located towards the cold end, before the throat. So i did experiment. Placing the heater block towards the cold end, just gives a very sharp temperature gradient == short transition zone and i prevent, that the transition zone is shifted to the nozzle. In terms of heat transfer the contact area has to be "maximized" (but not more as needed otherwise friction is increased). If the transition zone is large (or already shifted into the hot end), it just means that the surface temperature is smaller than possible - this means you lose thermal capacity. I did not try the Prometheus hot end, but various nozzles up to 35 mm long.
@Deckingman:
thanks for "enthusiastic", i am just a nerd….
If i do a quick google for me it seems that the last part is much longer than at e.g. e3d nozzles. Maybe i found the wrong drawings.The time in contact is for sure important, but not (always) the limiting factor. For a given viscosity, flowrate and nozzle you need a certain "pressure". As long as your thermal capacity is big enough, it doesn´t limit you. But e.g. if someone uses a 0.2 mm volcano nozzle the length of the noozle is for nuts, it just increases friction. If you try to print really fast with e.g. 0.5 mm increasing temperature helps - why ? Going from 210 to 240 °C gives only about 30/190 = 17 % more deltaT (which would give you exactly 17 % more speed), but the viscosity will drop by a factor of e.g. 2 or more.... and by that the pressure is reduced. Increasing the temperature wouldn´t help as much if the thermal capacity is the limitation. The pressure built up seems to be the limit.
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@vp:
If i do a quick google for me it seems that the last part is much longer than at e.g. e3d nozzles. Maybe i found the wrong drawings.
I'd say that you probably misinterpreted the drawing. It's an easy mistake to make because at first glance the labelling does show a 24mm long section at 0.4mm diameter but when you look closely, you see that this is counter bored to 2.0mm for 21 mm of that length, leaving just a 3mm long section of 0.4mm diameter. Trust me, I own enough of them to know that this is the case. But of course, the drawings on the web are all generic and if you order a Diamond with a larger diameter at the nozzle tip, then of course the 0.4mm diameter section at the bottom of the melt chamber is also increased. I have 0.5mm and 0.9mm versions as well as the "standard" 0.4mm.
As a Diamond hot end user who has proven that it is indeed possible to print at up to 300mm/sec with a 0.5mm nozzle by exploiting the fact that there are multiple melt chambers, without increasing temperature or extrusion multiplier, you'll understand my scepticism about your theory. As I said, no hard feelings but from my own tests, I can't bring myself to accept your hypothesis. 10/10 for enthusiasm though.
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Thanks for your feedback.
The length of the 0.4 mm hole of an e3d v6 0.4 mm nozzle is according to this drawing https://wiki.e3d-online.com/File:DRAWING-V6-175-NOZZLE.png 0.6 mm - that is slightly longer than the diameter and needed to give the flow a chance to develop an even speed profile.
According to this drawing http://reprap.org/mediawiki/images/7/73/Diamond_Nozzle.pdf the length of the 0.4 mm hole is multiple times longer than 0.4 mm - there is no value given, but just compare the diameter 0.4 mm to the length of the hole…. it can also be seen, that the longer part of 0.4 hole doesn´t have to take the whole flow rate, the flow rate there will be total flow rate/#nozzle. Unfortunately it is the wrong way to try to reduce the pressure by splitting the flow rate and multiplying the length of the 0.4 mm section, we have laminar flow, pressure drop is proportional with speed not with speed^2.
1. We have laminar flow. The pressure needed is proportional to the speed. The cross section and speed is proportional to the diameter^2. Therefore the pressure drop per length of a 0.4 hole is (2/0.4)^2 = 25 !!! bigger than compared to a 2 mm section. So we don´t have to care about the 2 mm length too much in a "laminar flow" thinking. But it makes a huge difference if the 0.4 section is longer than needed. The minimum length is limited to the development of the speed profile (a too short 0.4 mm section would give an uneven flow).
2. Experience tells us, that anything which reduces friction, reduces the needed pressure. A laminar flow doesn´t care about roughness, the roughness is covered by the laminar boundary layer. If reducing the friction reduces the pressure, this effects cannot be related to the "hydro dynamically" flow, there must be something else. I call it "friction" and this friction has to come from some where where the filament is not flowing like a liquid, so the laminar boundary layer has no effect. Therefore i assume it has to come from the transition zone. This friction part will be proportional to the surface which is proportional to the length of the transition zone. Everything which reduces the length of the transition zone will reduce the friction and the needed pressure.
The problem is now, that at a constant nozzle temperature increasing the thermal active surface (nozzle length * filament diameter * pi) will lead to a reduction of the temperature difference between metal (nozzle) and filament. From that follows, that the transition zone gets longer because the thermal flux rate (W/m^2) gets smaller and the friction increases. The best nozzle length is just as long as needed to melt the material. Anything in addition will just increase the friction. So if the speed is increased, the part (%) of the pressure which comes from friction is reduced and the part (%) of the pressure which comes from "flow" is increased, up to the point where flow part limits (or the thermal capacity).
3. There is no doubt that you can print > 300 mm/s with a diamond hot end, but what i meant is just you don´t need it. You don´t need that much "surface area" this is not a limitation for 0.4 mm nozzles. When it comes to bigger nozzles e.g. 0.8 mm the thermal capacity will be limiting much earlier, because the pressure drop is much smaller (0.4/0.8)^2 = 1/4 and the extrusion rate (== needed thermal capacity) at equal speed is much higher (0.8/0.4)^2 = 4 compared to a 0.4 mm nozzle. But in real life using bigger nozzles the real limitation will be cooling and not extruding, it is not hot end constrained then.
4. To sum it up. There are 3 major constraints (flow, friction thermal) and all can be limiting, but the thermal capacity is not a real problem using small nozzles.
A small nozzle will be limited by the pressure drop due to the flow, a big one by the thermal capacity. In between the friction will also be important. -
This is starting to become tiresome.
How do you explain the following?
Using a single input on the diamond hot end, with a 0.5mm nozzle, I can get up to about 120 mm/sec at my normal print temperature before I see signs of under extrusion having an adverse effect on print quality. This is consistent with what most people see with a standard E3D V6. According to your theory, this should not be possible because as you say the diamond has a "restriction" that is multiple times longer than the E3D V6.
Furthermore, we have established that the "restricted part" of a Diamond hot end consists of a 3mm long section followed by a 2mm section giving a total of 5mm@0.4mm diameter (although the diameter depends on nozzle size). So now when I employ all 3 inputs, the "restricted zone" becomes 3 x 3mm (3mm for each of 3 filaments) plus the "common" 2mm length. However you look at it, the "restriction" is far more for 3 filaments than a single one. Yet by employing all 3 inputs whilst keep the temperate and extrusion multiplier the same, I am able to attain print speed almost 3 times as high. Clearly the limiting factor in this case is NOT friction, nor the pressure drop.
The reason why I am able to print at higher speed using 3 inputs compared to a single input, has to be that I am employing 3 melt chambers. This has two advantages. One is the greater surface area of filament to hot surface and the other is that for a given speed, each filament spends 3 times as long in the melt chamber compared to a single filament in a single melt chamber. Thus the main constraint to printing at high speed is the melt rate of the filament and not friction or flow rate through the nozzle.
Forget all this stuff about Laminar flow too. It may sound good but it's not relevant over the tube lengths we are talking about. In any case you seem to have completely over looked the fact the molten filament is a non- Newtonian fluid.
As I've said, 10/10 for enthusiasm but your theory is ….... I'm trying to think of a polite way of saying "just wrong".
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Using a single input on the diamond hot end, with a 0.5mm nozzle, I can get up to about 120 mm/sec at my normal print temperature before I see signs of under extrusion having an adverse effect on print quality. This is consistent with what most people see with a standard E3D V6. According to your theory, this should not be possible because as you say the diamond has a "restriction" that is multiple times longer than the E3D V6.
Furthermore, we have established that the "restricted part" of a Diamond hot end consists of a 3mm long section followed by a 2mm section giving a total of 5mm@0.4mm diameter (although the diameter depends on nozzle size). So now when I employ all 3 inputs, the "restricted zone" becomes 3 x 3mm (3mm for each of 3 filaments) plus the "common" 2mm length. However you look at it, the "restriction" is far more for 3 filaments than a single one. Yet by employing all 3 inputs whilst keep the temperate and extrusion multiplier the same, I am able to attain print speed almost 3 times as high. Clearly the limiting factor in this case is NOT friction, nor the pressure drop.
The reason why I am able to print at higher speed using 3 inputs compared to a single input, has to be that I am employing 3 melt chambers. This has two advantages. One is the greater surface area of filament to hot surface and the other is that for a given speed, each filament spends 3 times as long in the melt chamber compared to a single filament in a single melt chamber. Thus the main constraint to printing at high speed is the melt rate of the filament and not friction or flow rate through the nozzle.
The point is that you need something which has multiple times of the surface than e.g. a single easy and light volcano nozzle to print at the same speed a volcano nozzle is able too. I never claimed that you cannot print 120 mm/s with a diamond hot end….. i print 150mm/s with a single e3d v6 nozzle.
Forget all this stuff about Laminar flow too. It may sound good but it's not relevant over the tube lengths we are talking about. In any case you seem to have completely over looked the fact the molten filament is a non- Newtonian fluid.
Laminar or not has nothing at all to do with "newton" or "non newton" fluid. The difference regarding 3d printing of the "non newton" aspects is that the viscosity will get smaller with increasing speed - that´s all. But compared to the temperature effect vs viscosity you can assume the viscosity to be constant in the 3d printing speed range.
The laminar boundary layer doesn´t know if the fluid is newton or not. Roughness doesn´t matter in a lamniar fluid dynamic sense for non newton as well as newton fluids. For friction roughness does matter.It may sound good but it's not relevant over the tube lengths we are talking about.
Why? What else does matter (beside the friction you say it also doesn´t matter) ? If the nozzle is tooooo long, you are right, the tip of the nozzle won´t be a problem, because of the problems described above.
Beside the popcorn i still believe that we can learn something useful from such discussions. Nobody is forced to read it and everybody is welcome to join;)
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http://www.sherv.net/cm/emoticons/drink/popcorn-and-drink-smiley-emoticon.gif
I have now moved to the spectating area too.
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Is there an emoticon for "yeah whatever…"?
@vp.
What we have is your assumption of what might happen according to your theory(s) vs my knowledge of what does happen based on practical testing. If you want to convince me that your theory is right and that there is some flaw in my testing then you'll have to build a hot end based on your theory and present some "real world" test results. From what you say, this hot end would have an extremely short melt chamber because you claim that thermal capacity is not the limiting factor but friction is. So you can then present you findings to E3D who would be delighted to learn that their Volcano design, with it's long melt chamber is entirely the wrong thing to do.Another little flaw in your theory is this "you can assume the viscosity to be constant in the 3d printing speed range".
That's not the case I'm afraid as PLA will hydrolyse (go less and less viscous). This process starts at about 170 degrees C and is a function of time as well as temperature. So at slow speeds, PLA is indeed much less viscous than at high print speeds due to time time that the filament has been heated. It's another reason why increasing the temperature helps with high speed printing.
I'd love to continue this discussion along the lines of the complex rheology of non-Newtonian fluids and hear your views on whether you consider molten printer filament to be a yield-pseudoplastic fluid obeying the Herschel-Bulkley model, but to be honest, I'm starting to lose the will to live.
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Is there an emoticon for "yeah whatever…"
Hi Ian,
This is as close as I can find…. (rolling eyes)(◔_◔)
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Very interesting…. God read
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I wish I had time to test the core suggestion that increasing extrusion multiplier non linearly will result in better high speed extrusion. It's surely just a case of printing a rectangle of the type Ian and I have both played with that allows max speed to be attained and then nudging the speed up with each layer and applying the increased extrusion multiplier. Well soon see if it works. VP what do you suggest should be the factor for the multiplier? Your other thread suggests a square relationship so % new extrusion multipler=%increase in speed2?
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Hi Dj, see here https://www.duet3d.com/forum/thread.php?id=3728 These curves are based on one of my "high-speed PLAs", that means it is flow improved. Other filaments start to increase much earlier/steeper.
I started with printing a cylinder in vase mode and increasing the speed and the extrusion multiplier together so far that it still worked out for me (the diagram in the link above was done differently, but that takes more time). For the beginning, a round object without corners should be fine. It should be big enough (e.g 150 -200 mm diameter) because in vase mode the layer time is really small and you will run into cooling troubles at higher speed. You need a constant flow, any acceleration is not welcome because you might get under extrusion. Or you are able to accelerate really fast. In this case, the extrusion rate disturbance is small enough to get filtered through the hot end/nozzle.
The curves shown in the link are "constant extrusion capacity" curves, without discontinuities of the flow rate.
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What we have is your assumption of what might happen according to your theory(s) vs my knowledge of what does happen based on practical testing. If you want to convince me that your theory is right and that there is some flaw in my testing then you'll have to build a hot end based on your theory and present some "real world" test results. From what you say, this hot end would have an extremely short melt chamber because you claim that thermal capacity is not the limiting factor but friction is. So you can then present you findings to E3D who would be delighted to learn that their Volcano design, with it's long melt chamber is entirely the wrong thing to do.
I am sorry deckingman, english is obviously not my mother tongue, but i don´t know what your comments have to do with what i have written ?!?
1. You say you can print with one diamond nozzle with 120 mm. One diamond nozzle has multiple times the thermal surface area of a single e3D v6 nozzle and i have no problem at all to print with a single e3d v6 (no volcano) 120 mm/s . Isn´t it obvious that the "thermal surface/ residence time" cannot be the limitation in this case (small nozzle) ?!?
2. You say if you use 3 instead of 1 nozzle you can print faster - big surprise, what else should happen ?!? Did you ever think of that your limitation is the pressure because of the much too long small holes in the diamond hot end ? If you divide the flowrate by 3, the pressure drop will be reduced and you are able to print faster. But compare the thermal surface of all 3 nozzles to a single volcano nozzle. I didn´t calculate it, but bet 1 diamond nozzle has much more thermal surface than 1 volcano nozzle. In your opinion, you should have to able to print at about 2000 mm/s and not 300 mm/s, if the thermal surface would be the limitation.You did the tests already, just see the truth !
Another little flaw in your theory is this "you can assume the viscosity to be constant in the 3d printing speed range".
Just read/quote the whole sentence, " But compared to the temperature effect vs viscosity you can assume the viscosity to be constant in the 3d printing speed range. " And this is 100% correct. Besides this, this is not part of "my" theory.
That's not the case I'm afraid as PLA will hydrolyse (go less and less viscous). This process starts at about 170 degrees C and is a function of time as well as temperature. So at slow speeds, PLA is indeed much less viscous than at high print speeds due to time time that the filament has been heated. It's another reason why increasing the temperature helps with high speed printing.
I don´t want to discuss what hydrolyse is, but i guess you mean "polymerize" in this content and that means it will coke up, and coke is not really something with a low viscosity. You want a test ? Just heat your hot end, feed it with PLA and bake a PLA cookie…. To "crack" PLA it takes much more than a 1-2 seconds at 240 °C and if you don´t remove the cracked chains fast enough you bake them quickly.
The reason why a non-newton fluid like molten PLA has a smaller viscosity at higher speed has nothing at all to do with the residence time or temperature in the hot end. If you increase the temperature the viscosity will be reduced significantly. I measure the nozzle temperature directly at the tip of the nozzle. If the speed is increased the viscosity will be reduced (=> non-newton) and not increased (and i compare at same nozzle temperature and nothing else) ! That is the only interesting part of the non-newton PLA fluid - but as already mentioned, it is too small to matter.
It's another reason why increasing the temperature helps with high speed printing.
I am glad that we found something we agree;)
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Why do I feel this sudden urge to start gnawing off my leg?
Just checked my calendar and it's not the first of April either.
(Deep breaths…......., stay calm)
VP,
You have no idea what a Diamond hot end is do you? It has 3 inputs but a single nozzle! A single filament goes through a single melt chamber which has roughly the same dimensions as an E3D volcano - not multiple times greater as you keep stating!When using all 3 inputs, each filament goes through a separate melt chamber but then into the same nozzle. So I'm NOT using 3 nozzles! It's still the same single nozzle! I say again, when I employ 3 inputs, it melts each filament in a separate chamber but then passes them all through the same single nozzle! If the nozzle is the same one, then the friction/resistance to flow is the same! In fact it's greater due to the restriction that each filament has to pass through before all 3 of them join and flow through the same single nozzle.
Only one nozzle is employed but the number of melt chambers feeding into that nozzle can be varied. I don't know how many different way I can state this. The only thing that changes when feeding 3 filaments into the single nozzle is the number of melt chambers employed before the filament enters this single nozzle.
And no, I do not mean Polymerize when I say Hydrolyse. I mean Hydrolyse when I say Hydrolyse. Do not twist my words then waffle on about Polymerisation because I never mentioned the word. Hydrolyse means become less and less viscous as I explained, and as I also explained, it is a function of time and temperature and so is relevant. It means that for PLA, viscosity is not a constant. Do not dismiss this just because you have never heard of it and assume that I mean something else.
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@vp:
You need a constant flow, any acceleration is not welcome because you might get under extrusion. Or you are able to accelerate really fast. In this case, the extrusion rate disturbance is small enough to get filtered through the hot end/nozzle…..............
So how does this have any value in real life printing which involves continuous changes of speed as well as acceleration\deceleration, to say nothing about retraction and un-retraction?
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So how does this have any value in real life printing which involves continuous changes of speed as well as acceleration\deceleration, to say nothing about retraction and un-retraction?
1. Yes of course, if you read and understand what this test is for, it should be clear. Before you tell your slicer which parameters are possible you have to know where the real limitations are. So you need to know what your 100 % baseline is. The "constant extrusion capacity " is a hard limit you cannot (without hardware or filament change) exceed. if you set you slicer to a limit above, you have to fail. To find out what your very hard limit is (the constant extrusion capacity), you have to have "constant "extrusion during the test, that is all.
2. Once you know how much you would have to adjust the extrusion multiplier, you are also fine with retracts (that means it won´t get better or worse). Of course, the extrusion multiplier has only to be increased in case you push and not pull.
3. If you know what is possible, you can start to think about how to utilize the real limits. The reason why i use 1-10 g (the higher the speed the more) of printing acceleration is to achieve an as much as possible constant extrusion flow rate - by that i don´t run too much into these problems. I set my extrusion multiplier to e.g. 1.5 for some features and because my average printing speed doesn´t drop too much it works.
If one print at 50 mm/s 0.5 g is enough to keep the absolute extrusion speed variance under a certain limit, which means the extrusion won´t be a problem. But at 200 mm/s you have to increase the acceleration. Otherwise, you will run into extrusion problems (without adjusting the extrusion multiplier). Retraction is the worst case. A lot of prints have huge sold bottom fills, there is no retraction and it takes a lot of time to print them slowly. It is no problem to print them fast - if the extrusion multiplier fits !4. To adjust the extrusion multiplier will give a lot of benefit at high (e.g. > 150 mm/s) printing speeds, but it will also improve quality below 100 mm/s. TPU is a very good example, but also PETG and even PLA can be improved.
5. The way i do it right now is to use a different setting for different features, e.g adjust the extrusion multiplier when i do solid infill, according to the max speed - but that is not a beautiful and by far not the optimal way.
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I have recently been scratching my head trying to work out why I am getting under extrusion with a titan upgrade to my mini Kossel and this thread discusses the problem I am seeing. Before I found this thread, while searching for anything related to under extrusion vs feed rate, I discovered this very interesting article that was written over 4 years ago http://www.extrudable.me/2013/04/18/exploring-extrusion-variability-and-limits/.
Edit: I forgot to add that (as mentioned in the above article) this effect occurs at very low feedrates. I did a very quick test with PLA at 200C using the titan and a 0.4mm JHead hot end and got the following extrusion factors:
[[language]] mm^3/s %extruded 2.4 97.5 4.8 95.5 7.2 92.5 12 90With the hot end not connected (just the bowden tube) I get 100%
So my current solution (not so optimal) is to up the extruder steps by 5% in the Duet config and then in the slicer (Cura), I reduce the first layer flow to 95% to avoid over extrusion due to the low speeds used for the first layer.
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There is a similar nobservation at http://forums.reprap.org/read.php?262,802277,803224#msg-803224.
I am seriously considering adding a feature to make extruder_drive_speed = f(requested_extrusion_speed) where f(x) = x + ax^2 + bx^3 for some values of a and b. The values of a and b will depend on filament and extrusion temperature. Calibrating them would be done automatically with the help of a Duet3D filament monitor.
