1 Topic by billyfingers

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Topic: Revised hot end

Having recently had quite a few issues with my stock Solidoodle 3 hot end- and currently awaiting some new parts from SD whilst my printer is down- I've taken to thoughts of designing a hot end that is a bit more serviceable. I've access to a small but plucky lathe in my personal workshop as well as a 2000lb milling machine and an absolutely monstrous 10' lathe at my workplace; so I figure why not see if I can whip something up.
Some of the design considerations I'm going to address are:
1- Clogs and just how to make clearing them out easier.
2- The heating element/resistor housing. I've seen some interesting articles on housings with two of these heaters in them so perhaps that would be an interesting route (though I think this may put too much heat too quickly into the head, leading to a burnt filament clog).
3- replacement of the peek with aluminum; I had given stainless some thought as well but I think that may simply keep the heat in whereas I can fin the aluminum to help dissipate it in the upper tract. Of course, the PEEK is there to insulate the upper tract so I may just make a goopy mess but that's half the fun of this stuff.
4-The "wood" mounting plate for the hot end on the SD3. I want to make an aluminum piece. It may act as a heatsink, it may cook the acrylic above it, or it may do nothing. I have some flat stock hanging about and just want to make a more...robust piece.

Well, I'm off to the workshop and will post some pics. I've got five pieces of brass hex stock, so I will make five variant prototypes.
Cheers.

2 Reply by billyfingers

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Re: Revised hot end

Here is the brass hex stock (.500" or 12.7 mm) I'll use. Total cost for these pieces was $15, it's a bit steep but still cheaper than my other hobbies.

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3 Reply by billyfingers

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Re: Revised hot end

Firstly, the nozzle shape was cut, followed by the filament passage and lastly the threaded shank diameter was turned down.

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4 Reply by billyfingers

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Re: Revised hot end

The thread was cut for 1/4-20, as I just like that thread. The first part of the thread is iffy, but functional. On the next one it'll be improved. As for the heater element body, it will be out of some aluminum stock I have lying about.

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5 Reply by cmetzel

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Re: Revised hot end

I admire your drive, but since you're making the brass barrel and nozzle out of one piece you'll have to unscrew the barrel from the peek in order to clear out clogs if you get a bad one, and that's not advisable.  How are you putting in the .35mm(.0137") hole though the end of the nozzle, how much land are you leaving for the .35mm hole in other words how long is the .35mm hole.  Also you're going to want to stay with the PEEK insulator, anything else is going to transfer heat too well and soften the filament too soon and you'll get kinks and clogs instantly. 

You should take a poll of users here and say "If you could make your own nozzle and had access to a machine shop how would you make it and start there.  There are some brilliant people hanging around this place.

6 Reply by billyfingers (edited by billyfingers 2013-03-24 02:10:11)

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Re: Revised hot end

Well put. As it stands I've got .060" from the tip of the nozzle to where the .0135" bore starts. I'm not sure just how much space to leave and how that affects the molten filament the further it gets from the centre of the heating element, or if that even matters at these distances ( .250"-.375" from bore start at nozzle end to centre of heating element); the bore length is rougly 1.350". I'll certainly make the next version out of two pieces and keep the PEEK as well. Thanks for the info as I'm sure it certainly will save me some time in the process.
For now I'll be using my one piece unit as a mock-up dummy unit for the other parts I'll be whittling.
Cheers and thanks again, I appreciate it.

7 Reply by billyfingers (edited by billyfingers 2013-03-24 03:31:36)

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Re: Revised hot end

So, using .875" (7/8") aluminum stock I've created the housing for the thermal resistor ( I'm unsure of the proper term for it) and a couple of things have become apparent:
I do not like having it thread on. I remember taking apart the stock hot end and just finding it a bit cumbersome. Of course this is one of those "personal taste above logic" situations I avoid like the plague in my professional life but boy is it bothering me. So, in a clear re-invention of the wheel I'm going to have it be secured by set screw.
Another thing is when using the round stock, drilling the hole on a radius is an interesting affair. It is not possible with a standard drill bit, so I used a spare .188" (3/16") end mill in my drill press with mixed results. It works, but a $75 drill press is put to task while doing it.
The resistor is entirely encased in the cylinder, and there is room for another on the other side but clearance may be an issue when the time rolls around to fit it in the hot end assembly. I may mill some flat spots to trim the fat, or turn the diameter down to .750" to avoid this.
I have some .35mm bits on order, and in the meantime will work on the three piece design.
All told not bad for an evening of prototyping.
Should anyone reading this have any suggestions ideas etc please don't hesitate to let me know as I'm game to try almost anything.

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8 Reply by cmetzel

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Re: Revised hot end

Are you planning to use a set screw against the threads?  You could mill a flat step into cylinder to give a straight shot through the part for the resistor?  I'm far from the expert but could the resister go vertically through that piece instead of horizontally?  Would it make any difference as long as the wires didn't get in the way? 

Where do you plan to mount your thermistor?  If I were making my own design I think I would put a little pocket in there where the thermistor could sit so I was assured it sat the same way each time. 

Last thing, I bought some .35mm bits from ebay with 1/8" shank and a small twist drill chuck that looks like a jewelers screwdriver.  I made the mistake of buying carbide though which together with a handheld twist drill makes for some pretty frustrating moments.  It came in a set of 10 with my plan being to drill out a clog I had rather than melting it with acetone, but since carbide is so brittle I snapped 5 straight before getting it to work.  I had intended to use them by hand without disassembling but I'd need plain steel ones not carbide to try that.  Took me forever to find the broken pieces on the kitchen floor. 

Good work so far, looking forward to watch the evolution.

9 Reply by danny

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Re: Revised hot end

Will that fit into the stock machine?

I've found that there is some limited space around the brass barrel before you'll be fouling the x carriage.

10 Reply by billyfingers

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Re: Revised hot end

Hi Danny just took the dial to it and it looks like there's .805" of space to work in ( .4025" from centre of peek) before the wall is met. I'll use a .750" dia puck and mill a flat spot on the back, may go so far as to take off .125" and make it a "D" shape. I'll be securing it with a set screw to a non-threaded portion on the connector shank so I don't have to worry about orientation. I think I'm quicky moving towards drawing this one out is SolidWorks.
Cheers

11 Reply by billyfingers (edited by billyfingers 2013-03-24 17:49:01)

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Re: Revised hot end

Okay,
working on the new space constraints I took five minutes on the lathe and somewhat haphazardly milled off a little over .125" from the existing proto-housing, making the "D" shape needed for clearance. This is an added step and a move towards the little square, asymmetrical design from SD, but I think with vertical thermosistor placement and set screw securement still maintains a few advantages. This one still has a horizontal thermosistor placement which I think I will be nixing, but if you are only using one I think it is still a better choice. Coincidentally, this morning I saw  a kickstarter project for one of these that looks near identical, so clearly I'm on the right track.
That being said I am fully prepared to go in any old direction so long as it improves the design.

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12 Reply by Manx

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Re: Revised hot end

Billy the one on kickstarter doesnt' look to fit the current solidoodle design hint hint

13 Reply by danny

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Re: Revised hot end

Other than "cause it looks sweet" (and that does look pretty good) why are you making the heater round? (now D shape?)

is there a benefit to this shape? (I think that there is probably a downside with increased surface area?)

other than that, as said above, making the nozzle and barrel the same piece will make it harder to clear clogs. if would seem like there is less to take apart, but there is more.

I'm not against removing the barrel from the peek, (in fact I'm working on a design myself very similar to this, the difference is that I'll be using 6mm aluminium rod and making the nozzle right in the barrel.)
a heater that screws on, (just like the one you've made, or the traditional heat-core that came with the machine.)
(there seems to be no point in having any hex type component to the nozzle if it's not detachable, (probably better to have a hex part further up the barrel as this can then start to act as a heat-sink hopefully dispersing the heat before it gets to the plastic carriage part.

Peek is used as an insulator because of it's high melting point and good thermal insulation. stainless steel is the only metal that has reasonable thermal characteristics (doesn't conduct well).

but peek does limit the temperature that you can print at...

with a longer barrel and heat sinking, you can attach a metal barrel to the machine and not worry about pre-mature melting, but the downside of this is that you need to sink away the heat very well, so that they top of the barrel stays cool. but the bottom of the barrel you need to heat like crazy to keep it hot enough!!!



Do you have a link for the kick starter one?

14 Reply by cmetzel

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Re: Revised hot end

http://www.soliforum.com/topic/1810/the … 5-hot-end/

15 Reply by billyfingers

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Re: Revised hot end

The cylinder- now "D"- shape is easier for me to chuck into the lathe and manipulate the shape; it's just a byproduct of the tool being used. I agree the two piece nozzle is the way to go, on the next iteration that's where I'll be headed.
Also I was unaware that stainless had such insulative thermal properties, I have some stock kicking about but I think I may stick with the PEEK. Then again, I may throw one together and test it anyways:)
Thanks for the info, this is turning into quite the educational experience. I think I'll head into the shop again tonight to make a new housing.
Cheers all

16 Reply by danny

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Re: Revised hot end

http://www.reprap.org/wiki/Thermal_Conductivity

there's a table.

Chrome nickel steel and stainless are the best metal insulators. (though there is question as to whether they are insulation enough)

given how cheap it is, (and how easy to work with) I might try making a mould of a block, and cast one from cement. (read I want to, but can't imagine having the time for a little while!)

look at the thermal conductivity of Granite, how good would a polished granite block look! smile (that would be very difficult to do though!)

for measurements on the grove mount style blocks that the solidoodle uses look here:

http://www.reprap.org/wiki/RB_Thermal_Barriers


I've created a new thread today with the new heater I did at the weekend:
http://www.soliforum.com/topic/1847/hot … placement/
It's a bit like the heater you're making except I'm using a heater stick instead of resistor, and mounting the thermistor in the block as well instead of taping it to the hot end so it should hopefully be more secure. (also mine is square as I don't have a lathe!)

feel free to incorporate or ignore any ideas that you might get from there.

17 Reply by cmetzel

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Re: Revised hot end

danny wrote:

I'm not against removing the barrel from the peek,

Not to say this is gospel, I've taken mine apart already a couple times but I don't think I'd make it mandatory if I was designing a hot end assembly.

http://www.soliforum.com/post/11089/#p11089

18 Reply by billyfingers

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Re: Revised hot end

Hi Guys,
I've done a rough D with some added features. Both Danny and Cmetzel mentioned a cavity for the thermosistor ( forgive me if I botch the term) which I thought was brilliant, so I made one at the rear face of the D (the flat bit) as near to where the nozzle starts as I dared and nice and close to the shank. I will fill the test unit's cavity with thermal paste and go from there. I chose the flat spot because it was the thinnest cross section so the bore of the cavity wouldn't need to be all that deep to prevent melted insulation on the wire, though I don't know if that would be an issue anyways. Another reason is that I've got a small out of space back there and I can offset it to the side which has the terminal; just to keep everything tidy.
Continuing with the set screw concept, I've added one to the side (10-24 thread) and bored a 5/16" hole in the centre where the 1/4-20 thread was in the previous iteration. Please note that the new shank will have a matching un-threaded portion for the screw to seat on, and will be a much tighter fit preventing the offset of the housing on the shank shown in the images.
The screw is located on the side because that makes loosening easy.
Were I to ditch the transverse mounted cavity for the heater resistor and go for two resistors, I would mount them vertically on eother side of a centrally located set-screw; which if I feel up to it tomorrow I may block out.
Cheers and thanks for the great ideas everyone, keep 'em coming.

Oh, I have found some 306 stainless stock in what looks like a rough approximation in size to the PEEK curerntly in my my machine, so it looks like I will have no excuse not to give that a shot too. You know it's funny that one of the most rewarding experiences I've had with regards to 3D printing and the Solidoodle has yet to involve any actual 3d printing with my Solidoodle.

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