building a hot end

Im getting ready build my hot end for my second prusa so i am assembling the parts needed and getting ready to machine but i have a few questions.

I have a question about the PTFE liner that is used in the J-head nozzles on the wiki page. Is it really necessary? What purpose does it have beyond preventing leaks? Does it insulate the filament from the hot metal sides of the drilled hole in the nozzle as to prevent the filament from melting before reaching the nozzles end? If its main purpose is to prevent leaks i might try and leave it out.

Don't leave it out. It provides a slippery surface for the filament as it softens and expands before the melt zone.

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The PEEK insulator should provide a slippery surface for the filament shouldnt it? Im just not understanding what the purpose is of lining the PEEK insulator with a PTFE tube rather than just drill the right sized hole in the PEEK and leave out the PTFE. If its absolutely necessary i will certainly use it.

PTFE is the most slippery substance known. That is why it is used for non-stick pans. PEEK is not very slippery at all and PLA will not slide against it when it has passed its glass temperature and become rubbery.

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[www.hydraraptor.blogspot.com]

With that said i certainly will use it then.

I would assume the reason for using PEEK for the insulator is its heat resistance, but any metal should also have great enough heat resistance. So i assume using the PEEK helps to prevent the heat from soaking in and transferring into the parts higher up such as the mounting plate? Is that correct. Anyone tried using standard yellow brass with lots of cooling fins or something similar?

You need to keep the heat in the melt zone.
It's especially important for PLA, it's why you'll see designs like the Budasnozzle and arcol that have heat sinks to cool the PEEK, and why people run fans pointed at the PEEK portions of the hotend.
if the hot area is too long for PLA the force of the extruder will cause the PLA to expand inside the PTFE liner and jam the nozzle, you'll either have to drill out the PTFE liner or replace it.

nophead Wrote:
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> PTFE is the most slippery substance known.

...snip
Second after diamond, but's quite ard to come by as a 3mm bore tube.

TC

My kit came with a peek only nozzle with a slightly out of centre drilled brass coupling. The friction was enormous(hard to extrude by hand). After a few nights of frustration I decided to make my own hotend with a pfte liner. As a new reprapper perhaps I should have just bought one bit it came out reasonably successful.

I still have to document it (shame on me). But it is called the frankennozzle. it combines the jhead all in one heater/nozzle and de arcol heat barrier ideas. The brass nozzle is good for extruding, the stainless steel middle section acts as a heat barrier, the aluminum heat sink get rid of the heat that does pass through.
The heater is enourmous and way to heavy for my weak x carriage and absolutely needs insulation (liquid gaskit for cars), the heat sink does not even get warm without insulation of the heater and little over body temperature when it is. In my current setup it undershoots instead of overshoots when heated and gives an extremely stable temperature when extruding (at 180C +- 0,3C).
In the near future i will make a lighter and smaller nozzle size version to replace this.

my recommentation is not to leave out the pfte.

I have the PTFE and PEEK and have my design cad drawn and ready to machine.

Does anyone know what type of plywood is used for most adapter plates, my Makergear kit came with a very hard ply and works great. I have tried balsa ply and aluminum neither of which worked for me. The aluminum transfers to much heat to the base of my extruder which causes it to soften and or warp.

If you have that much heat there, then your thermal break is not doing its job. You should be able to touch the end that makes contact with your extruder.

I am using the hot end from my Makergear kit and a wades extruder. I made my extruder from PLA but the Makergear nozzle mount plate wont fit the wades extruder without some modification thats why im trying to make my own mounting plate. I think if i had used ABS for the extruder it wouldnt be a problem. I checked the temp of the mounting plate after 30minutes of printing and if i recall correctly the aluminum plate was 130*F, the wood plate was about 100*F after 30minutes.

What are you calling the thermal break?

The thermal break is the PEEK/PTFE between your cold end (wade's, etc.) and your brass barrel/heater/nozzle. If you are getting that much heat at the mounting point then you may need a fan blowing on the top of your hot end. For me this is necessary using MakerGear or J-Head hot ends with PLA Wade's extruders, to prevent the extruder from softening, as well as to keep the hot end from jamming when printing PLA.

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GITRDUN Wrote:
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> I would assume the reason for using PEEK for the
> insulator is its heat resistance, but any metal
> should also have great enough heat resistance. So
> i assume using the PEEK helps to prevent the heat
> from soaking in and transferring into the parts
> higher up such as the mounting plate? Is that
> correct. Anyone tried using standard yellow brass
> with lots of cooling fins or something similar?

The material has to be able to withstand the heat, but it also has to prevent too much heat from reaching the cold end and melting the plastic too early. Brass has so good thermal conductivity that you would have to have a ton of cooling in the cold end if you made the heat break from it. Stainless steel has a conductivity of only about one tenth of brass and since it's stronger, it can also be made thinner, so you can make a PEEK-less heat break from it with very reasonable amount of cooling in the cold end. (Arcol V4 is one example)

Ok i have my hot end completed and put together. I made it similar to the j-heads. Im using a square 6061 aluminum block to hold the resistor and thermistor, screwed it onto the brass nozzle, which has a female thread in the other end to thread onto the cold end. I made two cold ends, one from PEEK and one from stainless steel that way i can test and compare the differences, i have 3 cooling fins machined into the cold ends and did use the teflon sleeve to keep the filament from sticking.

So i used some muffler putty to hold the resistor and thermistor in place and after a few hours of sitting i hooked it up and turned on the temp. It heated up extremely fast and after about a minute it blew out the putty plug i had in to keep the thermistor in place. Went off like a firecracker. Obviously there was some air left in the hole where the resistor sits and probably some in the hole where i have the resistor as well.

So is this an issue or does it not really matter that the resistor and thermistor are not secured in an air tight hole?

GITRDUN Wrote:
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.........
> So is this an issue or does it not really matter
> that the resistor and thermistor are not secured
> in an air tight hole?

On my J-head I wrapped the resistor with a strip of aluminum foil until it fit snug. Both the resistor and thermistor are held in with kapton tape, has been working fine.

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Thingiverse ID Alan1279

I have been working on the design on a reliable but cheaper extruder that is easy to make .
I am using the push mechanism from a Wade extruder to move the ABS so the concentration of the effort is on the hot end.
I am using a ¾ inch diameter brass piece turned to suit the extruding needs. Lined with Teflon tubing.
I am using nichrome wire insulated with tiny glass beads as the heating element.
An unusual insulator but effective. Since the wire is easily made red hot you have to watch that you don't melt the glass.
The wire is about 0.010 inches in diameter and it takes about 2 volts per inch to get it red hot.

I will make the drawings available on the net once I have the thermistor controlling the temperature properly and have run some tests further to make sure all is OK.

I am working on a large format printer that is easy to make and easy to disassemble to move (being large). It takes only one wrench and a small screwdriver to assemble everything!
The make envelope of the printer is a nominal 12 by 12 by 9 inches. So its a big printer. It will be available for sale as the Genesis 1 shortly.

You can Google me at “harprit sandhu” if you want to see where I am coming from.

Since nichrome wire is fairly hard to come by (in small quantities) and I have some left over, interested experimenters can have 12 inches for $6.50 ppd (via Paypal) in the US while my supply lasts. 12 inches is usually enough to make two heaters.
H

Had a chance to run two quick prints with the new nozzle and turned out good. Needs more tweaking to get it spot on but looks very impressive so far. I ran it up to temp with the SS cold end and the SS got wicked hot, so i switched to the identical PEEK cold end and it doesnt seem to even get above room temp. So the SS is out as a good heat reducer. Im stoked at how well this is working so far.

Been running my new hot end for about a week now with no trouble, not even a single jam. I let it sit for 30 minutes at extruding temp and it still didnt jam. Prints are coming out much better than my makergear hot end, i dont know why that is but im guessing its either in the calibration or the MG one needs a good cleaning out.

Only thing that has me a little puzzled is that i have to extrude at 230C with PLA. I dont know if this is typical of the J-head style or not. Or is it just a flaw in my design possibly. Maybe the thermistor isnt seated good enough to get a true reading. Doesnt really matter i guess as i it seems to be working great. But i would like to know why my temp needs to be so high.

Higher temperatures are typical for the J-Heads. I'm not sure exactly why, as I don't have a thermocouple to measure exact temperatures.

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It depends on the type and colour of the PLA. I can do Faberdashery red at 200C but blue needs about 240C.

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[www.hydraraptor.blogspot.com]