Peek, Brass Cylinder Madness

Hi Group,

I am in essence "almost printing". My 3D printer, of my own brew, is printing and for a little bit my extruder was outputting plastic. Hurray! Well, not so soon...

The problem I am having is that the plastic is melting in the peek and making a clog which pretty much renders all future printing impossible. I am also getting the entire brass barrel filled with plastic. Now, my brass barrel measures about 2 inches (roughly 50 mm). I have noticed that when I hit the hot end, the plastic backs up into the peek. This must be what is getting my peek gone.

If I make the barrel too short, however, then the peek melts and the barrels falls away. Something is not right, here. Where should I start with the trimming? A few other questions:

1. I do not installed the PTFE sleeve into the peek. Is this going to help with this problem, or is this sleeving for something else?
2. I have not installed a fan. Should I assume this would solve or help solve the problem as well?

I have been able to solve most of my problems by tinkering with the code and the electronics, but this one is one I am not certain how to tackle. I mean I can try a gazillion things but would definitely prefer to try the ones that are going to get me closer. I am so close to printing!!!

Thanks for your input!

JIQ

if you're melting peek then you've got it way way way tooo hot,

what temperature are you running?
i would maybe try either making the switch to a jhead or one of the all metal hotends currently available.

a picture says much are you willing to show us a picture of your hot end. from that we can diagnose a lot.

OK, I added some pictures here:

[www.avayan.com]

I think the problem is I am getting molten plastic in stages. The plastic very close to the hot end is in flowing conditions but as I go up into the barrel, I am getting the rubber consistency ABS. The rubber state is definitely a plug and if it gets bad enough to go into the peek cylinder, them I am hosed and I have to disasemble the hole thing.

I added the PTFE sleeve but that didn't solve the problem.

I am trying to run at 225C, but have gotten as high as 240C when I want to push the plug out. That helps, but at the top of the cylinder the plastic is close to hard.

I think the problem is the brass barrel is too long. Some options I will try before I shorten it will be to add a heat sink or a fan.

BTW, as you can see from the pictures this is a 90% home brew machine; I didn't make the ball bearings, screws, pulleys, belts or the shafts - well I'll be darned, that is almost 50% of this whole thing! Either way, I am having a blast making all these parts and making them work is part of the enjoyment. To buy an extruder would definitely solve the problem, as well as preserve whatever is left of my sanity, but would shave countless hours of fun ;-)

Thanks for your input!

JIQ

from the looks of it you have acces to a lathe. Make the thermal break section out of stainless steel not brass. It has a much lower thermal conduction coeficient, i.e. The heat wont travel up as much. And use a fan across the cold part of the hot end.

in this design using steal will not work, the barrel is too long , and steal is hard to machine. stainless steel will only work if it is lined with ptfe on the inside.

is your hollow diameter 3mm or slightly less? i only say this because if the hole is slightly bigger plastic will not melt enough as it goes down.

also i can't tell from the images, is the thermistor located right on the bottom near the hot end?

the thermistor should be as close as possible to the hot end. also the barrel needs to be insulated, as the entire area of metal needs to be at least 160degrees in order to allow feedstock thru.

i would insulate the barrel, wait 5 minutes after you reach temp and then try it again at 220-230.

it looks like you are using ptfe rather than peek. it that case you should get some plumbing tape (those metal rings with screws that adjust the diameter) get 2, and make sure the ptfe or peek barrier is drilled and threaded at least half way up, and the other side is at 3mm or slightly bigger (size is not as critical on pfte because it is a low friction surface). plumping tape should be tightened around the ptfe around where the barrel is.

it is very important your thermistor and setup is calibrated. what does your thermistor and set read temp wise at room temp?

Awesome input, guys!!!

OK, some data points:

1. Gulf, a little bit ahead of you. I changed from brass to stainless steel. Is it hard to machine? I"LL BE DARNED YES!!! Messed up a bunch of drill bits and then read on the web I was supposed to use cobalt drill bits, medium speed, lots of pressure and coolant. A quick trip to Lowes and harbor freight, and that stainless steel screw had been bored through in a snap!
2. I am running to the shop. How couldn't I think of this? Yes, my holes are 9/64" which is about 3.556 mm. I had known this for two days but as I read your message, a memory from decades ago snapped into my brain: air is an awful heat conductor! Hence, the filament is really not getting all the heat. All I need to do is drill some brass and some stainless steel and give this theory a try.
3. The barrel is peek, not PTFE. I bought it from McMaster-Carr. It is working fine and every now and then I remember to add the PTFE sleeving. I will not be able to use the PTFE sleeving on the stainless steel as the screw I am using is 0.25" (6.35 mm) and the sleeve I have is wider than this.
4. The thermistor ( a honeywell 135-104LAG-J01) is placed besides the brass barrel. I drilled a hole on the hot end body (made out of aluminum) and then placed the thermistor thru. Added cement putty and some kapton tape to make sure there are no shorts affecting the resistance. The thermistor reads 100K when at room temp, if I recall.

One question:

1. Cannot picture this: "plumping tape should be tightened around the ptfe around where the barrel is". Can you point to a picture detailing this step?

OK, will post an update once I add the 3 mm drilled brass segment. Thanks for these pointers!

JIQ

5.

try metal tie strap also. you want a metal ring that goes around the PEEK, and has a threading that turns to tighten it down. go to a plumbing store, or the garden section of a store.

If you are using 3mm filament, drill your brass/stainless tube to 3.2mm. Much more and filament will buckle in the tube, as it softens with the rising heat from the hot end. Molten filament can flow back up the barrel if it gets hot enough, and the extra friction will jam the barrel.

PLA/ABS when heated up will stick to PEEK when stationary, especially if the PEEK is getting hot, which is why it needs to be lined with PTFE. It doesn't stick to Brass, Aluminium and PTFE. I'm not sure about Stainless Steel, I don't think it sticks, but it is difficult to machine and perhaps the availability of 0.35mm carbide tipped drills stops it being used as much for the nozzle, I expect! Also, it doesn't conduct heat as well as brass and aluminium. But once it's up to temperature, it also doesn't lose heat as quick, either. Josef Prusa has made hot ends from SS - see his photostream here: [www.flickr.com]

What you want is a short, high temp melt area, and then the rest of the barrel losing temperature as quickly as possible. In the past, this has been done by insulating with PEEK. Now more designs are coming out that have a narrow SS part (as it can't conduct heat quickly) and actively cool the top part with a fan, similar to the Makerbot designs. For another example see [forums.reprap.org]

You've probably looked at a lot of hot end designs. I built my own similar to your design initially, then bought a mendel-parts V9, which I still use (which is nearly all brass barrel - see [forums.reprap.org] ) and a J-head Mk IV (see [reprap.org] ). I'm now working out how to get an all metal hot end, as I'm keen to start printing with higher temperature, more exotic materials like Nylon, Polypropylene and PET, where any PEEK or PTFE would melt.

This guys design will work after he does some modifications. Give him credit for going where not many others do.

There are a lot of assumptions that people have because of the marketing for different designs. All you really care about is that it keeps a stable temperature, flows at the rate you like it to and has some control around oozing. Some people also like the fact that some hot ends are shorter, and allow more build room.

Hi Guys!

Thanks to all for your input and words of encouragement! Had to leave the project behind for a few days to focus on work, but am back. Here is an update on how I am still not extruding as I should. I have to say that I do see more plastic coming out, but still not enough to print.

At work I validated the thermocouple is working as it should. I used a Fluke thermal imager and a Fluke thermo couple and the three systems compared correctly. I also tried two infrared thermometers and they were off like crazy. One of them was from Radio Shack and the other from Harbor Freight tools. I guess I got what I paid for...

I figured the nozzle hole was too small, so went with a larger one. I was using a #80 drill bit which is about 0.35 mm. I went up to 5 mm.

I also changed my hot end design from one resistor to two, Now I am using 24V instead of 12V. This is OK as my motor drivers can take up to 45V.

I added a fan, but I think it is too big as it cools down the hot end and does not let it reach the target temperature. For example I was trying to heat up to 210C, but with the fan I could not go above 185C.

I changed from brass/stainless steel to just brass. I also tried different lenghts from long to short. At the moment I am at 1.25" which is about 31.8 mm.

The brass barrel I tried to drill with 2 mm and with 3 mm ID. The 2 mm ID was too small and at the moment I am using the 3 mm ID one. PLA filament is 1.75 mm.

I think I am close. I can see some plastic coming out but I need to push myself and eventually it clogs completely. I guess the problem is the plastic removes the heat from the hot end and the PID loop is not fast enough to reheat it. I have never read of people tinkering with the PID loop, but maybe I should...

I have tried with different feed rates, but will need to experiment more on this aspect. But even if I make the printer run slow, it is not slow enough. Regardless, I have seen other printers operating fast, so I truly hope I don't need to run this Turtle Express technology and have to wait a week to see a part come out.

I also plan on adding more friction into the freewheeling ball bearing by placing it into a teeth sleeve. Doubt that's going to help much as sometimes I can't push with my hands, so chances are the stepper will not be able to push either.

So there is still some room to play with and I am not giving up. I am just baffled because I see so many extruders working out there and this one is really not that different! I wonder if the plastic I bought is made of polimerized adamantium... Is there such a thing as junk ABS or junk PLA? I bought both from Amazon. Anybody ever having issues because of the plastic itself? Haven't read about this either.

JIQ

Hi there,
Could you post a picture or two of your latest construction? I'm trying to visualise what you have at this stage from your description and a picture would help.
What size filament are you designing for 1.75mm or 3mm?
Is your filament diameter reasonably consistent?
How far does the brass now run into the PEEK insulator?

When a hotend is working well you can push plastic through it by hand with a little effort, even by turning the large gear wheel by hand. If you find you are having to apply greater force by improving friction on the filament or increasing motor torque, then the hotend design isn't as good as it could be and you are compromising.

If your brass rises too far into the peek then the heat will be conducted up inside the peek and soften the inbound filament too early, causing it to deform and jam. In brass barrel designs you see the brass either only travel a short distance into the peek, or else get fitted with a ptfe sleeve inside the brass.

The ptfe sleve is low friction and allows smooth movement of the filament. ptfe on it's own has proven poor because it expands too much if it warms up. Peek is stable, even at greater temperatures, but is a bit grippy if filament is fed through it.

The diameter of the hole that runs from the top of your insulator right through to your melt chamber should be slightly larger than your filament but not so large that your filament is loose inside it.

Keep at it if you enjoy the challenge. Share your progress and I'll be happy to comment based on my experience. I have experimented with building hotends. I did go down the stainless route a while back. The key to stainless upper is a smooth hole down the middle and the reduced neck diameter between the upper and lower portions. It needs to be reamed after being drilled to get the hole smooth. It needs the narrowed neck to reduce the crossectional area of the barrel, reducing heat flow upwards. It doesn't need a ptfe sleeve if the inside has been finished well. The stainless barrell can be short, which makes it easier to drill, now that you've mastered drilling stainless! But with a stainless upper you face new design challenges in what to do at the lower end/nozzle, and how they should meet, and not leak.

With a stainless 'neck' people tend to anchor them into an aluminium upper block. This is to rob the heat that manages to rise through the stainless barrel.

Regards for now,
NumberSix

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[numbersixreprap.blogspot.com]

Thanks NumberSix!

Here is a link to my most current extruder: [www.avayan.com]

Now, before I continue with yet another list on how this does not work, allow me to report that I think I have finally stepped into the world of 3D Printing!

Yesterday I decided to remove the last piece of brass (the hot end nozzle and brass barrel) and change them for aluminum. So I took a 1/4" piece of aluminum rod, drilled it, threaded it and VOILA! I was printing!

Well, OK, not so fast. There was one last element which required my attention. The PTFE sleeving was coming out of the PEEK barrel. It was then when I understood a previous comment to fix the sleeve with tape. I tried some kapton tape but this didn't work.

As you can see on the pictures on that website, there is a hollow screw that goes at the highest side of the PEEK barrel. Basically, this applies pressure into the PTFE sleeve and makes it impossible for it to let the backing plastic touch the PEEK, which was what was creating most of my deadly plugging scenarios. Once I applied this final touch, I was able to start printing.

I still need to add some improvements to the entire printer, but I think my hot end dilemma has been solved. I am of course now entering an even more exciting (as well as nightmarish) endeavor which is that of tuning the printer. Something tells me I'll be bickering on this forum in a not so long time ;-)

Thanks to all for the help and input! Would not have been able to do without it!

JIQ

Well done!
Happy printing!