Josef Prusa's Next Gen Hot-End (Print Nylon, Peek & PC)

Don't know what is more interesting on this thread...the new hot end design or the comments (More efficient resistors????). Anyway, I digress:

While the proof is in the pudding, this looks like a potentially very elegant and effective design. It looks (as best I can determine from the picture) that it is a two piece design...what I will call the barrel and the heat block.

All the angst in the comments about stainless being a poor heat conductor I believe is potentially misfounded. It appears (again, based on one picture) that the barrel can be very thin in the lower region where it is in contact with the heat block. I would see no reason that the heat block itself is not aluminum for very good conductivity.

This looks like a case of good engineering...making the tradeoffs. In this case: use stainless steel because it *is* a poor conductor of heat (but will take basically any temp you throw at it in terms of melting polymers) and is structurally strong so that the heat won't climb up to the filament drive area and melt the filament before it can be driven...then thin the barrel out where it clamps to the heat block (stainless is relatively strong...my guess is that you could get away with under a millimeter thick wall...maybe 0.5 mm...and get adequate strength. I am no mechanical engineer, but it would seem that that section of the barrel is under a compression (hoop) loading by the heater block that may actually make the combined structure stronger (comments on this theory, please).

Then add grooving in the mid to upper barrel to promote convection heat loss to cool the upper barrel.

What you now have is potentially a one piece...*no* seams...combined feed channel and melt chamber that you can heat pretty much as hot as you want.

It was hard to hear on the video interview with Josef, but I believe he said he needed to polish and lap the inside of the barrel...my guess (if I heard correctly) so that the plastic does not stick (thereby eliminating the need for the PTFE liner). That may be one of the key requirements to make a metal barrel work.

If I have the time/energy tonight, I will try to estimate/calculate how inefficient the use of a thin stainless wall between the barrel and the heater is compared to, say brass (which is not as good as aluminum but is commonly use as a barrel material) and even copper. My guess is that it is pretty good if kept reasonably thin.

Can't wait to find out more.

Polygonhell Wrote:
-------------------------------------------------------
> If you have one of the 12V 40W cartridges and are
> comparing that, then they have lower resistance
> and draw more power than the typical resistors
> used in reprap hotends.

Fits into the same hole on the hot end, but produces more heat driven by the same circuit - as I said, more efficient.

> I'd also assume that more regular shape gives them
> a more consistent contact area, and since air is a
> good insulator that probably helps.

Fits into the same hole on the hot end, but produces more heat driven by the same circuit - again, as I said, more efficient.

>
> I really don't think we have to discard things
> like the conservation of energy to explain your
> observation.

I'm not suggesting that don't observe that law, I'm suggesting that what is happening in practice is more relevant than what that law says "should" happen.

> And for the sorts of devices, temperatures,
> voltages and current that we're talking about Ohms
> law is more than adequate.

Yes, if you wish to remain inside that box of thought, it is...

But, why not explore other, possibly more efficient ways of achieving this?

Believing the world was flat, and all of the supporting theories, laws and general beliefs of the times was also more than adequate for the purpose it served...

Edited 1 time(s). Last edit at 01/03/2013 06:24PM by Tekwizard.

Tekwizard Wrote:
-------------------------------------------------------
> A 100 watt light bulb produces a
> fraction of the heat that a 100 watt wire wound
> resistor does given the same voltage applied, and
> the newer light bulbs generate so little heat that
> you can touch them with your hand.

That's plain wrong, if they have the same resistance they will generate virtually the same heat. "Newer light bulbs" generate less heat because they are lower power.

> I am well familiar with the formula's you've
> quoted guys, but thinking inside the box like that
> is only for engineers - the cartographers of of
> open minded thinkers paths.

If you refuse to learn, you are either trolling or an idiot. Please stop wasting our time.

Edited 1 time(s). Last edit at 01/03/2013 08:13PM by bobc.

mars bonfire Wrote:
-------------------------------------------------------
> Don't know what is more interesting on this
> thread...the new hot end design or the comments
> (More efficient resistors????). Anyway, I
> digress:
>
> While the proof is in the pudding, this looks like
> a potentially very elegant and effective design.
> It looks (as best I can determine from the
> picture) that it is a two piece design...what I
> will call the barrel and the heat block.
>
> All the angst in the comments about stainless
> being a poor heat conductor I believe is
> potentially misfounded. It appears (again, based
> on one picture) that the barrel can be very thin
> in the lower region where it is in contact with
> the heat block. I would see no reason that the
> heat block itself is not aluminum for very good
> conductivity.
>
> This looks like a case of good
> engineering...making the tradeoffs. In this
> case: use stainless steel because it *is* a poor
> conductor of heat (but will take basically any
> temp you throw at it in terms of melting polymers)
> and is structurally strong so that the heat won't
> climb up to the filament drive area and melt the
> filament before it can be driven...then thin the
> barrel out where it clamps to the heat block
> (stainless is relatively strong...my guess is that
> you could get away with under a millimeter thick
> wall...maybe 0.5 mm...and get adequate strength.
> I am no mechanical engineer, but it would seem
> that that section of the barrel is under a
> compression (hoop) loading by the heater block
> that may actually make the combined structure
> stronger (comments on this theory, please).
>
> Then add grooving in the mid to upper barrel to
> promote convection heat loss to cool the upper
> barrel.
>
> What you now have is potentially a one
> piece...*no* seams...combined feed channel and
> melt chamber that you can heat pretty much as hot
> as you want.
>
> It was hard to hear on the video interview with
> Josef, but I believe he said he needed to polish
> and lap the inside of the barrel...my guess (if I
> heard correctly) so that the plastic does not
> stick (thereby eliminating the need for the PTFE
> liner). That may be one of the key requirements
> to make a metal barrel work.
>
> If I have the time/energy tonight, I will try to
> estimate/calculate how inefficient the use of a
> thin stainless wall between the barrel and the
> heater is compared to, say brass (which is not as
> good as aluminum but is commonly use as a barrel
> material) and even copper. My guess is that it
> is pretty good if kept reasonably thin.
>
> Can't wait to find out more.

Being able to build the walls thinner on stainless is simply a silly argument, there is no real structural requirement of hot ends as they have very small amounts of "tool pressure" and really only serve as a guide for hot plastic. (I've cut 6061 down to .01" wall thickness before, with no issues) All I'm trying to say is that, in this case, you could build thin walled copper/aluminum/brass just as successfully as you could thin walled stainless. Regardless, copper is vastly more efficient in terms of conductance and would thereby apply more even temperature, faster, and more consistently than stainless. Comparing conductivity in terms of k, (Btu/hr-ft-F), Copper can be around 226k compared to stainless at a meager 6.5k - only 35x more conductive. Even just plain old 6061 aluminum has a value of 104k - only 16x more conductive. The link provided said his design is ALL stainless. So, maybe (hopefully) the heater block is made of aluminum and it's just not well described?

ALSO, take a look at Makerbots extruder (CU-BD copied it) which has a stainless insulating rod, brass nozzle, and aluminum heat block, as well as an additional stainless insulating block that the stainless insulating rod screws into - I believe makerbot uses a heat cartridge and cu-bd offers a resistor or cartridge. They don't use ptfe or peek either - I highly doubt a "lapped or polished barrel" is required. If you use a decent machine with decent tools, you can get a good finish that is at least as smooth as is required.

I'm not sure there is anything revolutionary, remotely special, or even new about this design - at least not that has been mentioned. I'm wondering if people are excited about it solely because it is a "Josef Prusa" design?

bobc Wrote:

> If you refuse to learn, you are either trolling or
> an idiot. Please stop wasting our time.

Nobody is twisting your arm to respond Bob.
If you feel your time is being wasted, then ignore what I have to say, and do something else.
I don't recall asking you, or anybody else to "teach" me anything.

Actually you can ignore bob too right? If you feel so right about your theory.

I think he feel the need to respond because this is a public forum where people come to for information. Sending incorrect information is worse than sending no information at all.

I seriously don't get all the prusa hype. They all looked like copied designs to me.

Tekwizard Wrote:
-------------------------------------------------------
> bobc Wrote:
>
> > If you refuse to learn, you are either trolling
> or
> > an idiot. Please stop wasting our time.
>
> Nobody is twisting your arm to respond Bob.
> If you feel your time is being wasted, then ignore
> what I have to say, and do something else.
> I don't recall asking you, or anybody else to
> "teach" me anything.

Actually, you did :

Tekwizard Wrote:
-------------------------------------------------------
>I would be interested if you could demonstrate that a hot end that uses a 5 ohm 5 watt carbon film resistor as a
> heater, is able to heat the nozzle to operating temperatures using the same amount of electricity as a 5 ohm 5 watt
> wire wound resistor. If not, can your formula's explain why not? How about you Nophead?

Post nonsense, challenge people to explain it, lie about what you said. Classic troll.

This is crazy. It isn't debatable. It's like arguing black is white. If resistors had an efficiency rating show me a data sheet that gives a value for this important design consideration? They are all 100% efficient at producing heat. Other things like light bulbs, that have resistance, but are not resistors, produce a little less heat because they produce light but paint it black and it will produce 100% heat.

If a resistor dissipating 40W of electricity doesn't produce 40W of heat where does the remaining energy go? Or is Tekwizard claiming the law of conservation of energy is wrong?

---

[www.hydraraptor.blogspot.com]

Pazu Wrote:
-------------------------------------------------------
> I seriously don't get all the prusa hype. They all
> looked like copied designs to me.

I guess that a famous name, a novel design feature, and a lack of published information to go on leads to a lot of hype/speculation. Regardless of theory, how the thing performs in practice won't be known until many people have tried building/using it.

The design has a nice elegant look, and the two part construction appears to reduce the part count to bare minimum. I suppose that preparing the stainless steel barrel takes more time though.

Prusa has some more pictures on his flickr account, and a couple of videos on youtube. In one picture he shows the heater got hot enough to melt its cladding. Ceramic heaters can easily get hot enough to melt aluminium.

The higher temperature pushes things forwards in terms of higher temp plastics, but as you note this is not the only all metal design. I would be more interested to see if it enables higher print speeds.

I would very much like to know more about the other all metal designs that have been alluded to. Are the details of these designs documented somewhere so that I can study them?

I am particularly interested in how they perform in terms of upstream filament sticking to the barrel. Seems to me, that is the reason so many designs employ a PTFE liner. Note: I am not knocking this approach but I think it is fair to say it limits the temperature range and *if* it can be eliminated, would be a good thing (flame suit on...).

A couple of further thoughts (maybe best called musings) on the new Prusa hotend.

As regards the choice of a cartridge heater. No question that if the design considerations were only limited to heating the melt area, stainless would not be the choice. But *if* one concluded that when all design considerations were taken into account (high temp, no seams to leak, maybe even a teeny bit of structural...oh, silly me.., keeping the upper barrel cool enough, keeping the heater block reasonably small, others?) and one decided (maybe just to rile up the reprappers) to choose stainless, then one may need more power from the heater element and this could lead to consider the use of a cartridge heater (was that tiptoey enough to keep hackles in place?).

Now just to prove I am not worshipping the design or the designer, one apparent knock on the design (again based on scant info), is that in appears that the nozzle is part of the barrel and that *if* one decided that it needed changing due to damage or clogging, it would require changing out a fairly complex (expensive?) piece of metal. Might be a good tradeoff in terms of no seams, and intial cost of product but may be a problem in terms of cost of ownership?

As someone pointed out, it is not clear how the temperature sensing is done. Any clues if this is just a thermisor in the heater block and if so, anything special about location? My guess is that if the block is aluminum or something of high thermal conductivity, it doesn't matter much?

I would like to add that my main interest in this discussion is not the specific design being analysed but rather to learn from the experts on this forum about the design considerations (material choice, heating methods, filament sticking, need to replace parts/maintenance, and many others) . It appears to me that the hotend design is still a dynamic and fertile area of interest and pivotal to the quality of the machines and that we are not at the final design (yes, even with this design).

I thought I would take a cut at calculating the impact of using stainless versus aluminum for the walls of the melt chamber portion of
the barrel of the new Prusa design.

The following are my assumptions (please review and comment):
* The thermal conductivity of aluminum is roughly 250. Watts/(meter-degreeK)
* The thermal conductivity of stainless is roughly 19. Watts/(meter-degreeK)
* Without access to the actual dimensions of the hot end, I am guesstimating that the heater block-to-barrel
interface can be modelled as a cylinder of 0.5 inches tall and 0.25 inches diameter with a wall thickness of
0.020 inches.
* To simplify, even though the shape is cylindrical, assume because of the relative thinness of the wall to the
height and diameter, that a reasonable model is a rectangular "prism" shape of the same thickness and equivalent area
* Ignore end effects.

Using Fourier's Law relating heat flow to temperature (fancy language for basically the Ohm's law of heat):

q = kA dT/s

Where :
q = heat (power)
A = heat transfer area
k = thermal conductivity of the material
dT = the temperature difference across the material
s = material thickness

For discussion purposes, assume a heat source capable of delivering 40 Watts (I believe fairly reasonable for a cartridge heater).
Assume the full 40 Watts flows through the wall into the melt chamber. This assumption should lead to
the biggest possible temperature delta (I believe this is correct?) between the heat source (block) and the chamber.

So plugging into the above for aluminum and after converting area and thickness to meters and solving for dT:

40 Watts = (250 Watts/(Meter-degreeK)) * 2.54 x 10 -4 sq. meters * dT/ 5.1 X 10 -4 meters
dT = 0.32 Degrees K (or C)

Calculating now for stainless steel with the same geometry:
dT = 4.24 Degrees K (or C)

This appears to indicate that the temperature drop is many times bigger for stainless than aluminum as expected
but is relatively (based on my sensibilities...YMMV) small compared to the melt temperature of the plastic. If, as one of the posters was
confident he could achieve (a 0.01" thick wall...i.e. twice as thin) while maintaining sufficient structural integrity,
the temperature drop for the stainless drops to 1/2 of this value or 2.12 Degrees K (or C).

Again, please check my calculations and assumptions...and I leave it to the designer to decide if
a 2 or 4 degree drop across the chamber wall is unacceptable given the full set of considerations in the overall design.

The biggest wrong assumption here I think is the "all heat goes into the barrel" assumption. Much of the power is lost through convection/ conduction. Also, the heater isn't on all the time (wouldn't run at 40W). Both these things will make the temperature difference smaller. So the use of stainless is not a big problem assuming your calculations are correct.

I agree. All the heat won't go into the melt chamber. My intent with using the assumption of "all the heat" was that it would worst case the temperature difference. Even with that overly conservative assumption, the temp difference was about 4 degrees. As you correctly point out, since realistically, less than the full heat flows into the chamber the temperature difference is even smaller, further supporting my contention that the use of stainless is not inherently the wrong choice.

as one of the few people who have successfully built and all metal hotend which is in use across multiple printers,
the only critical thing i can say against the "PrusaNozzle" :

- the series of small constrictions really should be replaced by one long one,

- he should really show the aluminium plate it comes with in the photo

other than that it's a pretty sound design and it's a design i might lean towards in the future for my hotends, the argument on wall thickness isn't particularly well founded as it takes no consideration as to length or structural integrity and is based on nothing but theory, in practice its a combination of wall thickness and length of the thin wall section in a stainless steel thermal barrier that makes the difference,

here is two stainless thermal barriers, with a wall thickness of 0.5mm with lengths or 20mm(for 3mm filament) and 12mm(for 1.75mm filament)
click here

you could not realistically make a thin wall section out of aluminium or copper or brass like this without it being really fragile especially at 0.01" which is 0.254mm to put it perspective is about as thick as two sheets of 80gsm printer paper(dependant on manufacturer),

if you add up the lengths of all the thin wall sections on the "PrusaNozzle" you will find that the numbers are somwhat similar there, looking at the mk7 and the qu-bd the contricted sections are too short, and the design is too reliant on the heatsink and a fan to keep it operating, both designs would work much better if they increased the lengths of those sections,

with heaterblocks in most cases a bare cartridge heater or resistor will struggle to keep a hotend at it's target temperature and the pid functions in most of the latest firmware do wonders to help this, somthing as simple as the mozzle traveling between two points is enough to start cooling a hotend let alone sustained motion

to try and calculate anything with these hotends you have to take into consideration a very large number of variables, variables which by the way change and fluctuate with things like travel speed feedrate flow rate, current temperature, ambiant temperature ,where temperature is measured, average flow for the last 30 seconds, ..... etc just to name a few,

Edited 1 time(s). Last edit at 01/04/2013 05:48PM by thejollygrimreaper.

Pazu Wrote:
-------------------------------------------------------
> Actually you can ignore bob too right? If you feel
> so right about your theory.
>
> I think he feel the need to respond because this
> is a public forum where people come to for
> information. Sending incorrect information is
> worse than sending no information at all.
>
> I seriously don't get all the prusa hype. They all
> looked like copied designs to me.


True, but then I'm not complaining about my time being wasted, am I?

bobc Wrote:
-------------------------------------------------------
> Tekwizard Wrote:
> --------------------------------------------------
> -----
> > bobc Wrote:
> >
> > > If you refuse to learn, you are either
> trolling
> > or
> > > an idiot. Please stop wasting our time.
> >
> > Nobody is twisting your arm to respond Bob.
> > If you feel your time is being wasted, then
> ignore
> > what I have to say, and do something else.
> > I don't recall asking you, or anybody else to
> > "teach" me anything.
>
> Actually, you did :
>
> Tekwizard Wrote:
> --------------------------------------------------
> -----
> >I would be interested if you could demonstrate
> that a hot end that uses a 5 ohm 5 watt carbon
> film resistor as a
> > heater, is able to heat the nozzle to operating
> temperatures using the same amount of electricity
> as a 5 ohm 5 watt
> > wire wound resistor. If not, can your formula's
> explain why not? How about you Nophead?
>
> Post nonsense, challenge people to explain it, lie
> about what you said. Classic troll.


I read an article in an american psychology magzine a number of years ago about IQ's Bob, and the relationship between them and individuals who resort to name calling (Troll, Liar, Idiot etc...), and other negative labellings of their fellow human beings, and they had found that the IQ and emotional maturity of such individuals was inverse to the number of times they resorted to such childish behaviors. They even went so far as to say that this sort of imature emotional behavior was just one step below - having a tantrum.

Do you know what a forum is Bob? It is a place, in this case a virtual place, where individuals with their own opinions and points of view can come and share those unique points of view with others. You don't "see" my point on any of this, so you become emotionally distraught and riled up and you attempt to shout down what I have to say. That kind of behavior belongs in either of two places, parliments and governments during debates when it's done purely for theatrics, and in kindergarten, and perhaps the early grades of school.

Troll, Liar....Idiot.....Really Bob?

You can't use engineering terms like efficiency and expect to be taken seriously when you are really meaning effectiveness. Heater cartridges may well be more effective, but that will be because they produce more power or have better thermal transfer characteristics but they are not more efficient.

As a point to note...our cartridge heaters certainly do not struggle to keep it at targer temperature, in fact we have run ours continuously at 350c with no problems (not extruding plastic, just moving around at printing speed).

Although we have recently come up with an odd solution to this...typically drilling very deep with a small diameter drill bit causes problems, either through shattered bits or a huge increase in machining time. We could make the same nozzle/barrel as Josef but it wouldn't cost anywhere close to the same cost as our stainless barrels ($8) due to a lot of extra machining time, although it wouldn't be anywhere near what he is charging (probably more like $20). Therein, to us the weakness of the design is cost, especially if there is a clog, damaged tip or a desire for a change in orifice size. Otherwise it looks pretty solid.

Chelsea - QU-BD

Chelsea - QU-BD Wrote:
-------------------------------------------------------
> As a point to note...our cartridge heaters
> certainly do not struggle to keep it at targer
> temperature, in fact we have run ours continuously
> at 350c with no problems (not extruding plastic,
> just moving around at printing speed).
>
i'm not suprised there, the hotend part looks to be completely shielded from the cooling fan on the heatsink!,

whats the hysteresis in temperature while printing? it's one thing to get it to a target, it's another thing to keep it as close to it as possible,

> Although we have recently come up with an odd
> solution to this...typically drilling very deep
> with a small diameter drill bit causes problems,
> either through shattered bits or a huge increase
> in machining time. We could make the same
> nozzle/barrel as Josef but it wouldn't cost
> anywhere close to the same cost as our stainless
> barrels ($8) due to a lot of extra machining time,
> although it wouldn't be anywhere near what he is
> charging (probably more like $20). Therein, to us
> the weakness of the design is cost, especially if
> there is a clog, damaged tip or a desire for a
> change in orifice size. Otherwise it looks pretty
> solid.
>
> Chelsea - QU-BD

you should see what the local cnc shops around here charge(australia), to put a 2mm hole in some stainless threaded m6 rod(20mm long), would cost me nearly $30 for 1 and if i wanted to get the price down i'd have to order over 2000 to get the price to $11 a piece, i might call you guys,

Edited 1 time(s). Last edit at 01/04/2013 07:18PM by thejollygrimreaper.

nophead Wrote:
-------------------------------------------------------
> This is crazy. It isn't debatable. It's like
> arguing black is white. If resistors had an
> efficiency rating show me a data sheet that gives
> a value for this important design consideration?
> They are all 100% efficient at producing heat.
> Other things like light bulbs, that have
> resistance, but are not resistors, produce a
> little less heat because they produce light but
> paint it black and it will produce 100% heat.
>
> If a resistor dissipating 40W of electricity
> doesn't produce 40W of heat where does the
> remaining energy go? Or is Tekwizard claiming the
> law of conservation of energy is wrong?

Of course I'm not claiming that the law is wrong. Heat is light, albiet at a slow wavelength that we can't see, but it is still just light. An ideal resistor would be one that did not heat up, because it would last longer. However, in order to stay in line with the law, it could perhaps convert that energy into a much higher spectrum of light - like a light bulb does, or even higher so that there is no felt heat. That energy that would normally be felt as heat to us, would instead be converted to something we could see, but not feel. The law would not be ignored. At a higher spectrum, that energy would still be accounted for, but it would not cause nearly the same amount of damage as a resistor that just heated up.

Other things,

This debate started way back on page one when Traumflug said in reference to Joseph Prusa's use of ceramic heaters in his new hot end:
- IMHO, heater cartridges are a waste of money. No technical advantage over wire resistors.
To which I reponded by telling how I had experience with both and that I could attest to the fact that the ceramic heaters are much more efficient at the task than a resistor,
Which caused Nophead to declare that: "All resistors are 100% efficient. They convert electrical energy to heat, nothing else."
Which caused me to disagree and say that resistors are used to resist (impede) the flow of electrons in an electronic circuit and that heat is a by-product of their design and that more efficient devices could be used to impede the flow and they would in effect be more efficient at the task...

Which caused Bobc to border on a tantrum and start calling me names...?

Here in a nutshell is my point of view:

A device to create heat = a heater
A device to create light = a light bulb
A device to impede the flow of electrons = a resistor.

All three devices can be made more or less efficient.

A heater without a blower fan = inefficient
A heater with a blower fan = more efficient.

A light bulb painted black = inefficient
A light bulb that generates more heat than light = efficient

A resistor that gets really hot and burns up when it passes 40watts = inefficient
A resistor that convert 40 watts to a high spectrum light (a light bulb?) = more efficient.
Those big honking 40 watt resistors we used to use in the 1950's = inefficient
Modern ceramic 40 watt resistors that don't need heat sinks = much more efficient.

If you're right Nophead that the primary function of a resistor is to generate heat, then I'm wrong.
However, If I'm right that the primary function of a resistor is to resist (impede) the flow of electricity in a circuit, then there is always room for improvement in the design of the devices.

Definition of efficiency according to Wikipedia: Efficiency, the extent to which time or effort is well used for the intended task or purpose

Edited 1 time(s). Last edit at 01/04/2013 07:44PM by Tekwizard.

Greg Frost Wrote:
-------------------------------------------------------
> You can't use engineering terms like efficiency
> and expect to be taken seriously when you are
> really meaning effectiveness. Heater cartridges
> may well be more effective, but that will be
> because they produce more power or have better
> thermal transfer characteristics but they are not
> more efficient.

It is not an engineering term, although engineering uses it. It is a common term that is part of everyday english.
Definition of efficiency according to Wikipedia: "Efficiency, the extent to which time or effort is well used for the intended task or purpose"

A heater, designed to generate heat is doing is fulfilling it's intended purpose, but that is not the intend task or purpose of a resistor.

It makes me chuckle a little to think that a few RepRap Icons (nod to NopHead and Greg Frost) are here arguing the semantics of the term efficiency.

Don't waste your brain power on this, go work on your next awesome designs!

It is my belief that heater cartridges will eventually be accepted as more effective than heater resistors

Edited 1 time(s). Last edit at 01/04/2013 07:48PM by Idolcrasher.

Dear jollygrimreaper,

I am woefully ignorant of your design but would like to find out more. Have you or Is it possible to make the design details available? As I mentioned in my post, I am particularly interested in hearing if you had any problems with the filament sticking which as I understand it (again, correct me experts) is the reason that people use PTFE liners and if you needed to make special accomodations in the all metal hotend to deal sticking (special polishing? surface treatment? special geometry?).

Can I assume since you have make a workable all metal hotend you believe that is the way to go?

TIA.

Tekwizard Wrote:

> Of course I'm not claiming that the law is wrong.
> Heat is light, albiet at a slow wavelength that we
> can't see, but it is still just light. An ideal
> resistor would be one that did not heat up,
> because it would last longer.

It might be your ideal resistor but it doesn't exist. Resistors slow down electrons and in doing so turn the kinetic energy of the electrons to heat, which is vibrational energy. The heat produced is always the same. You might think the primary function of a resistor is to slow down electrons. You might think the primary function of a wire is not to slow them down. In reality the both have resistance and produce exactly the amount of heat according to P = I^2 R or V^2/R.


>However, in order to
> stay in line with the law, it could perhaps
> convert that energy into a much higher spectrum of
> light - like a light bulb does, or even higher so
> that there is no felt heat. That energy that would
> normally be felt as heat to us, would instead be
> converted to something we could see, but not feel.
> The law would not be ignored. At a higher
> spectrum, that energy would still be accounted
> for, but it would not cause nearly the same amount
> of damage as a resistor that just heated up.

You are saying a light bulb is a more efficient resistor than a resistor? Well that is an odd way of looking at things but yes it produces less local heat, but it produces light which travels and produces heat at distance when it is absorbed. If you put a light bulb inside a sealed tin it will heat the tin exactly the same as a resistor dissipating the same power, or a cartridge heater. From the outside you would not be able to tell the difference.


>
> Other things,
>
> This debate started way back on page one when
> Traumflug said in reference to Joseph Prusa's use
> of ceramic heaters in his new hot end:
> - IMHO, heater cartridges are a waste of money. No
> technical advantage over wire resistors.
> To which I reponded by telling how I had
> experience with both and that I could attest to
> the fact that the ceramic heaters are much more
> efficient at the task than a resistor,
> Which caused Nophead to declare that: "All
> resistors are 100% efficient. They convert
> electrical energy to heat, nothing else."

Yes

> Which caused me to disagree and say that resistors
> are used to resist (impede) the flow of electrons
> in an electronic circuit and that heat is a
> by-product of their design and that more efficient
> devices could be used to impede the flow and they
> would in effect be more efficient at the task...

But you don't understand electronics or physics. If you slow down electrons with a resistance you get heat. The amount of heat is defined by the Ohm's law not by the construction of the resistor.


>
> Which caused Bobc to border on a tantrum and start
> calling me names...?
>
> Here in a nutshell is my point of view:
>
> A device to create heat = a heater
> A device to create light = a light bulb
> A device to impede the flow of electrons = a
> resistor.

Yes they are named by their primary function but they all obey the same rules of physics and they all convert electrical energy to electromagnetic radiation with 100% efficiency. The only thing that changes is the frequency spectrum.

>
> All three devices can be made more or less
> efficient.

Only at their primary function. Bulbs create a lot of heat so are not very efficient at producing light.

Heaters are 100% efficient unless they get hot enough to glow and then produce a little light.

But both are 100% efficient converting electrical energy to electromagnetic radiation. The distinction between heat and light is just an artefact of our eyes and nerves.

Resistors (the electronic devices of that name as opposed to things having resistance) do not emit light so they are 100% efficient at converting electrical energy to heat. As are most electronic components by the way: transistors, capacitors, etc. Any power lost in them appears as heat.

>
> A heater without a blower fan = inefficient
> A heater with a blower fan = more efficient.

No actually. A fan heater is better at distributing the same amount of heat energy more evenly over a distance.

>
> A light bulb painted black = inefficient
> A light bulb that generates more heat than light =
> efficient

A bulb painted black becomes a heater, 100% efficient at heat generation.

>
> A resistor that gets really hot and burns up when
> it passes 40watts = inefficient
> A resistor that convert 40 watts to a high
> spectrum light (a light bulb?) = more efficient.

No both produce exactly the same amount of heat. The temperature they reach is determined by how quickly heat is lost. So a small resistor will get hotter but the heat it loses to the environment is exactly the same. If it gets hotter than it can handle it will fail but that is not inefficiency.


> Those big honking 40 watt resistors we used to use
> in the 1950's = inefficient
> Modern ceramic 40 watt resistors that don't need
> heat sinks = much more efficient.

No there is no such thing as an efficient resistor. Put a 40W resistor in a tin and it will warm it the same amount regardless of it construction. A resistor that can handle a higher surface temperature can be smaller for the same power dissipation but it will give exactly the same amount of heat to its environment.

>
> If you're right Nophead that the primary function
> of a resistor is to generate heat, then I'm
> wrong.

Resistors reduce the flow of electricity by producing heat. Whether you think of the heat produced as a primary or secondary function doesn't affect the efficiency of that process. The two things are inseparable.

Think of a valve (or vacuum tube). That also impedes the flow of electrons but in quite a different way to a resistor. Nevertheless the amount of heat it produces will be determined by the current through it times the voltage.

> However, If I'm right that the primary function of
> a resistor is to resist (impede) the flow of
> electricity in a circuit, then there is always
> room for improvement in the design of the
> devices.
>
> Definition of efficiency according to Wikipedia:
> Efficiency, the extent to which time or effort is
> well used for the intended task or purpose

The primary purpose of a resistor is to reduce the flow of electricity but it only does that by creating heat, so it is always 100% efficient.

A resistor placed in a heater block produces exactly the same heat a cartridge heater dissipating the same power. They are both the same thing, a coil of nichrome or constantan wire wound on a ceramic former cemented into a metal container. They both have 100% efficiency.

A cartridge heater has a regular outside shape so you can slide it into a close tolerance hole and the job is done. They cost many times more than a resistor. Most are too big so they make the heater block bigger and thus waste a lot of heat. So in terms of heating the hot end they are actually less efficient. Also the power tends to be too high to be safe without a thermal fuse.

Vitreous enamel resistors are much cheaper but they have an irregular outside shape. You have to cement them into a clearance hole. They then last forever. They get a bad name because people try to use a push fit, hold them in with Kapton or glue them in with silicone. They will fail unless the air gap is filled with a thermally conductive cement.

Because resistors are available in smaller packages and any resistance you want they allow a smaller heater block, which is more efficient as it has lower surface area, so loses less heat. And you can pick a value which won't get too hot even if they are on 100% due to a fault.

Vitreous enamel resistors are only rated for a surface temperature of 350C so cartridge heaters have the advantage of being able to run at higher temperatures but they are in no way more efficient.

Edited 3 time(s). Last edit at 01/04/2013 09:28PM by nophead.

---

[www.hydraraptor.blogspot.com]

you can see some images of it here
and i'm putting the finished touches on the drawings for the "V1 ALUHOTEND" so i can put them up somwhere,

the ptfe liners used in some are really just guides to get around interfacing section between two pieces, to avoid this i run a 2mm drilbit down the filament hole after it's been screwed together, and with the thread reduced a small amount you can get a near seamless interface which won't grab the filament,

as for special treatments, internal honing and polishing doesn't seem to make any real difference that makes the process worth it, (for those who are going to ask "how do you hone the inside of a 2mm hole?", a piece of string and some grinding paste)

filament sticking is somthing i've managed to avoid, on mine as long as the cold side is kept cool the constricted section doesn't get hot enough to soften pla,so what i get is solid plastic all the way to the meltzone, which in V1 is only 10mm long, essentially it has no "softzone" or at least a very very short one,

when i first started making them i was able to extrude abs and pla with no active cooling, however these days given the incredible variance between batches of pla and abs and things like melting points it's easier for me to just say use a fan on the heatsink

as for the way to go, i've got a bit of a mixed view on it, there isn't really no general one size fits all hotend,
some are suited for high speeds but perform poorly at lower speeds some really only work well with abs and not pla some work really well with pla, and some are really good all round,
i think there is a lack or realworld testing of these things which looks at a wide range of variables, which is why i'm putting together a test stand with a power supply and arduino based datalogger just for testing extruders and hotends,







mars bonfire Wrote:
-------------------------------------------------------
> Dear jollygrimreaper,
>
> I am woefully ignorant of your design but would
> like to find out more. Have you or Is it possible
> to make the design details available? As I
> mentioned in my post, I am particularly interested
> in hearing if you had any problems with the
> filament sticking which as I understand it (again,
> correct me experts) is the reason that people use
> PTFE liners and if you needed to make special
> accomodations in the all metal hotend to deal
> sticking (special polishing? surface treatment?
> special geometry?).
>
> Can I assume since you have make a workable all
> metal hotend you believe that is the way to go?
>
> TIA.

nophead Wrote:
-------------------------------------------------------
> Tekwizard Wrote:
>
> > Of course I'm not claiming that the law is
> wrong.
> > Heat is light, albiet at a slow wavelength that
> we
> > can't see, but it is still just light. An ideal
> > resistor would be one that did not heat up,
> > because it would last longer.
>
> It might be your ideal resistor but it doesn't
> exist. Resistors slow down electrons and in doing
> so turn the kinetic energy of the electrons to
> heat, which is vibrational energy. The heat
> produced is always the same. You might think the
> primary function of a resistor is to slow down
> electrons. You might think the primary function of
> a wire is not to slow them down. In reality the
> both have resistance and produce exactly the
> amount of heat according to P = I^2 R or V^2/R.
>
>
> >However, in order to
> > stay in line with the law, it could perhaps
> > convert that energy into a much higher spectrum
> of
> > light - like a light bulb does, or even higher
> so
> > that there is no felt heat. That energy that
> would
> > normally be felt as heat to us, would instead
> be
> > converted to something we could see, but not
> feel.
> > The law would not be ignored. At a higher
> > spectrum, that energy would still be accounted
> > for, but it would not cause nearly the same
> amount
> > of damage as a resistor that just heated up.
>
> You are saying a light bulb is a more efficient
> resistor than a resistor? Well that is an odd way
> of looking at things but yes it produces less
> local heat, but it produces light which travels
> and produces heat at distance when it is absorbed.
> If you put a light bulb inside a sealed tin it
> will heat the tin exactly the same as a resistor
> dissipating the same power, or a cartridge heater.
> From the outside you would not be able to tell the
> difference.
>
>
> >
> > Other things,
> >
> > This debate started way back on page one when
> > Traumflug said in reference to Joseph Prusa's
> use
> > of ceramic heaters in his new hot end:
> > - IMHO, heater cartridges are a waste of money.
> No
> > technical advantage over wire resistors.
> > To which I reponded by telling how I had
> > experience with both and that I could attest to
> > the fact that the ceramic heaters are much more
> > efficient at the task than a resistor,
> > Which caused Nophead to declare that: "All
> > resistors are 100% efficient. They convert
> > electrical energy to heat, nothing else."
>
> Yes
>
> > Which caused me to disagree and say that
> resistors
> > are used to resist (impede) the flow of
> electrons
> > in an electronic circuit and that heat is a
> > by-product of their design and that more
> efficient
> > devices could be used to impede the flow and
> they
> > would in effect be more efficient at the
> task...
>
> But you don't understand electronics or physics.
> If you slow down electrons with a resistance you
> get heat. The amount of heat is defined by the
> Ohm's law not by the construction of the
> resistor.
>
>
> >
> > Which caused Bobc to border on a tantrum and
> start
> > calling me names...?
> >
> > Here in a nutshell is my point of view:
> >
> > A device to create heat = a heater
> > A device to create light = a light bulb
> > A device to impede the flow of electrons = a
> > resistor.
>
> Yes they are named by their primary function but
> they all obey the same rules of physics and they
> all convert electrical energy to electromagnetic
> radiation with 100% efficiency. The only thing
> that changes is the frequency spectrum.
>
> >
> > All three devices can be made more or less
> > efficient.
>
> Only at their primary function. Bulbs create a lot
> of heat so are not very efficient at producing
> light.
>
> Heaters are 100% efficient unless they get hot
> enough to glow and then produce a little light.
>
> But both are 100% efficient converting electrical
> energy to electromagnetic radiation. The
> distinction between heat and light is just an
> artefact of our eyes and nerves.
>
> Resistors (the electronic devices of that name as
> opposed to things having resistance) do not emit
> light so they are 100% efficient at converting
> electrical energy to heat. As are most electronic
> components by the way: transistors, capacitors,
> etc. Any power lost in them appears as heat.
>
> >
> > A heater without a blower fan = inefficient
> > A heater with a blower fan = more efficient.
>
> No actually. A fan heater is better at
> distributing the same amount of heat energy more
> evenly over a distance.
>
> >
> > A light bulb painted black = inefficient
> > A light bulb that generates more heat than light
> =
> > efficient
>
> A bulb painted black becomes a heater, 100%
> efficient at heat generation.
>
> >
> > A resistor that gets really hot and burns up
> when
> > it passes 40watts = inefficient
> > A resistor that convert 40 watts to a high
> > spectrum light (a light bulb?) = more
> efficient.
>
> No both produce exactly the same amount of heat.
> The temperature they reach is determined by how
> quickly heat is lost. So a small resistor will get
> hotter but the heat it loses to the environment is
> exactly the same. If it gets hotter than it can
> handle it will fail but that is not inefficiency.
>
>
> > Those big honking 40 watt resistors we used to
> use
> > in the 1950's = inefficient
> > Modern ceramic 40 watt resistors that don't
> need
> > heat sinks = much more efficient.
>
> No there is no such thing as an efficient
> resistor. Put a 40W resistor in a tin and it will
> warm it the same amount regardless of it
> construction. A resistor that can handle a higher
> surface temperature can be smaller for the same
> power dissipation but it will give exactly the
> same amount of heat to its environment.
>
> >
> > If you're right Nophead that the primary
> function
> > of a resistor is to generate heat, then I'm
> > wrong.
>
> Resistors reduce the flow of electricity by
> producing heat. Whether you think of the heat
> produced as a primary or secondary function
> doesn't affect the efficiency of that process. The
> two things are inseparable.
>
> Think of a valve (or vacuum tube). That also
> impedes the flow of electrons but in quite a
> different way to a resistor. Nevertheless the
> amount of heat it produces will be determined by
> the current through it times the voltage.
>
> > However, If I'm right that the primary function
> of
> > a resistor is to resist (impede) the flow of
> > electricity in a circuit, then there is always
> > room for improvement in the design of the
> > devices.
> >
> > Definition of efficiency according to
> Wikipedia:
> > Efficiency, the extent to which time or effort
> is
> > well used for the intended task or purpose
>
> The primary purpose of a resistor is to reduce the
> flow of electricity but it only does that by
> creating heat, so it is always 100% efficient.
>
> A resistor placed in a heater block produces
> exactly the same heat a cartridge heater
> dissipating the same power. They are both the same
> thing, a coil of nichrome or constantan wire wound
> on a ceramic former cemented into a metal
> container. They both have 100% efficiency.
>
> A cartridge heater has a regular outside shape so
> you can slide it into a close tolerance hole and
> the job is done. They cost many times more than a
> resistor. Most are too big so they make the heater
> block bigger and thus waste a lot of heat. So in
> terms of heating the hot end they are actually
> less efficient. Also the power tends to be too
> high to be safe without a thermal fuse.
>
> Vitreous enamel resistors are much cheaper but
> they have an irregular outside shape. You have to
> cement them into a clearance hole. They then last
> forever. They get a bad name because people try to
> use a push fit, hold them in with Kapton or glue
> them in with silicone. They will fail unless the
> air gap is filled with a thermally conductive
> cement.
>
> Because resistors are available in smaller
> packages and any resistance you want they allow a
> smaller heater block, which is more efficient as
> it has lower surface area, so loses less heat. And
> you can pick a value which won't get too hot even
> if they are on 100% due to a fault.
>
> Vitreous enamel resistors are only rated for a
> surface temperature of 350C so cartridge heaters
> have the advantage of being able to run at higher
> temperatures but they are in no way more
> efficient.

Nophead, I appreciate your point of view, and the effort you've put in to explain it.
I don't agree with everything that you've written, but I think that might be in part to our unique interpretations of what is "efficiency".
I think that I've laid my perspective out clearly, as have you yours.

Thanks


Edited 1 time(s). Last edit at 01/05/2013 12:28AM by Tekwizard.

Electronic engineering is not a point of view. The simple equations governing how much heat a resistor makes were established more than 100 years ago and are accepted by anyone working in that field.

Your central argument is that resistors have difference "efficiencies" but no matter how you define what that is they simply don't. They all, without exception, convert electrical energy to heat 1:1.

---

[www.hydraraptor.blogspot.com]

My $0.02 regarding "efficiency":

The AFAIK most common heater resistor is 5.6 ohms and with that you get 12V * 12V / 5.6 ohms = 25.7 watts at 12V. This cartridge apparently has 40 watts, so it heats up a lot quicker. Maybe this is recognized as "more efficient", because it simply has more power.

The solution would be to use resistors with 3.3 ohms, which would produce 44 watts of heat. And a reasonably heat conducting, temperature withstanding cement, like nophead already pointed out.

There are also drawbacks in using oversized (as in high wattage) heaters: temperatures change quicker, local overheats are higher, so you get more material aging. With or without a cartridge.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

the real plus for me regarding the heater cartridges is the fact that they are very smooth and round and are easier to stuff into a heater block.

It is also nice that they traditionally have some wires coming off of them, so I get to skip the step where I crimp wires onto the resistor. The wires are short and need extending though...

Anyone got a guesstimate as to the length of sevice life of a heater cartridge vs. a heater resistor that is in "regular" RepRap service?

FYI: The Hong Kong based group "RepRap Discount" is selling heater cartridges on eBay. Heater Cartridges on eBay

I have not tried these particular heater cartridges, but I would love to know what people think of them.

Their stuff is cheaply made, but has always worked for me. They have very prompt customer service. If you are going to sell your soul to the devil and buy from China, start by checking out RepRap Discount (eBay) or my other favorite cheap but reliable Chinese company, Repraper.com