Teflon spacer replacement

[3poro 9]

I went back to the original fan, it was taking a LOT longer to heat the head and the temperature was oscillating quite a lot.. It would need some calibration to keep that fan, or an enclosed box.

 

Yes, heating takes longer - which is actually a good sign - the cooling gets more efficient. Of course, in the design of the print head there should be better insulation between the nozzle/heating block and the aluminium structure.

What comes to temperature oscillation, see the last messages over here:

http://umforum.ultimaker.com/index.php?/topic/6307-um2-twin-tornadoes/

...so it looks like there's some problem with the fan output, if even a single Tornado causes such a problem.

 

[3poro 9]

If you are printing at 260C, then the spikes before PID settles down are surely above 265C, the temperature at which PTFE breaks down - even at temps near that, it turns brown and loses structural integrity, as you have demonstrated.

The solution is don't print over 245C if you want the spacer to last. Check the vendors printing temp recommendations - I'd be very surprised if 260C is suggested.

 

On Ultimaker's ABS filament spools the temperature is indicated as "<265C" and 260C is the UM2's default nozzle temperature for ABS. If I use anything below 255C, I don't get very good layer-to-layer adhesion and also the risk for under-extrusion grows.

 

[eldrick 65]

I print my products using ABS at 238C, and it stays structurally sound under Olympic competition use.

 

[donmilne 2]

Hmm. I wonder if the glass filled teflon is more susceptible to abrasion, especially with lots of retractions.

 

[3poro 9]

Hmm. I wonder if the glass filled teflon is more susceptible to abrasion, especially with lots of retractions.

 

I think this is the problem. The new Teflon piece has stayed in shape from outside perfectly - it still has very good fit with the stainless steel isolator. However, the ridge is more distinct and sharper in shape than in my original (old type) Teflon piece - even if the old one got slightly malformed and wouldn't fit inside the stainless steel isolator without using a lot of force.

 

[3poro 9]

I print my products using ABS at 238C, and it stays structurally sound under Olympic competition use.

 

What can I say - lucky you. I'm now having my 3rd temperature sensor and with all the sensors the ABS behavior has been similar - so I don't think my nozzle temperature reading is somehow off. Given the problems the high temperatures are causing, I really wouldn't mind using lower temperatures. Every time I have made any bigger changes to my system, I have tried using temperatures around 235C..245C with ABS - and every time I have been thrown back to use higher temperatures. In my opinion UM2's default temperature of 260C (for ABS) makes sense.

 

[donmilne 2]

I've been rereading this thread with a view to turning my own spacer at the weekend. What was the verdict re PEEK vs PTFE?

Cleven talked about PEEK to begin with and then I think switched to PTFE? Daid asserted that one PEEK test jammed within an hour, but didn't suggest why that should be the norm.

I have both PEEK and PTFE rod here so I'm somewhat neutral, though PEEK seems harder and easier to machine.

Comments?

 

[cleven 4]

I found that the peek and ptfe for me was virtually the same. I only went with ptfe because I had some bar stock of it. Made it much easier to make. It is also easier to cut than peek .

Peek did give some issues when removing the filament but that was all I noticed.

 

I've been rereading this thread with a view to turning my own spacer at the weekend. What was the verdict re PEEK vs PTFE?

 

Cleven talked about PEEK to begin with and then I think switched to PTFE? Daid asserted that one PEEK test jammed within an hour, but didn't suggest why that should be the norm.

 

I have both PEEK and PTFE rod here so I'm somewhat neutral, though PEEK seems harder and easier to machine.

 

Comments?

 

[3poro 9]

If I understand the heat dispersion in the nozzle unit correctly - and referring to simulations made by Kris - I think the temperature of the Teflon isolator drops pretty quickly (vertically, from bottom upwards). In other words, only the first couple of millimeters are really vulnerable. Two ideas for brainstorming:

 

1. What if the isolator's filament hole was drilled a bit bigger for the first 4mm from the bottom - and there was a very thin-walled tube inside it? If its walls were thin enough, it wouldn't act as a strong enough transport for heat to cause problems for the upper parts of the Teflon isolator. As the weight of the tube (3.2/3.8mm(?) in diameter, 4mm? in length) would be minimal, it could be made out of almost any material (like gold) from cost perspective.
    
   
2. There could be a thin isolator ring between the brass nozzle unit and the Teflon isolator - just thick enough to reduce temperature transfer by a bit. If the ring was thin enough, maybe it wouldn't be a catastrophe even if PLA would stick to it? Ceramics? PEEK? http://www.extreme-bolt.com/Products-PI-Washers.html ?
   

 

The latter would naturally be a very easy solution - even a failed PTFE isolator could be used as a basis after cutting off the malformed bit of it.

 

[DidierKlein 729]

Damn the new glass Teflon doesn't last long?

I just changed my old Teflon to the new one, and i intend to print with XT at temps higher than 240°c

For info here's a pic of the old and new (unused) Teflon side by side:

 

[donmilne 2]

That ridge doesn't look like wear to me, or even heat distortion (though heat may play a part). It looks to me like the plastic has been formed around a former of some kind... e.g. around the top thread of the brass nozzle, perhaps while the nozzle was being fitted?

 

[eldrick 65]

How about a ceramic washer for insulation between teflon piece and the brass? It shouldn't cause enough friction to be an issue.

 

[donmilne 2]

Anyone have any tips on the easiest possible way to get that spacer out of the UM2 printhead and back again?

 

[solid-print-3d 30]

It wouldn't be so bad if the Teflon insulator was just considered a consumable, much like a mig welder tip, or a plasma cutter tip, and sold in bulk at a reasonable price. As it is now, they're $20 each!!! Maybe a bag of 5 for $20? That way we can just burn through them, and replace when needed. At $20 each, it's no wonder people are trying to turn every conceivable material to try to come up with a better solution. You don't see people saying "I've got to come up with a better mig tip!" That's because they're $1.50 each! Use it up, and put a new one on. Maybe that's just my strange way of thinking?

 

[3poro 9]

You don't see people saying "I've got to come up with a better mig tip!" That's because they're $1.50 each! Use it up, and put a new one on. Maybe that's just my strange way of thinking?

 

It's not a strange way of thinking, but the cases are not quite analogue. First, you can't easily check whether the Teflon isolator is worn out or not. In order to check it, you'll have to take the print head into parts - which is not fun. Second, if you decided to just change the consumable once a week to be on the safe side, changing of it is not fun.

 

[cleven 4]

Hold the phone people!, all this hubbub! Just simply make one in a lathe yourself. Which obviously everyone should own , Problem solved

Well technically it would be nice if they were a bit longer then you could trim down the end more and at least get a few uses out of them, since the wear is at the bottom

 

[solid-print-3d 30]

I think they'll last more than a week? And to me, it's not very hard to disassemble and replace the head. I think I can change the insulator in under 5 minutes. You could do it at regular service intervals.... Change the insulator, grease the Z, lube the rods, clean up scrap filament under bed. If it's still good, then save it. Same thing with other consumables like the mig tips. Often times you can just sand the tip to a nice copper finish. Likewise, you can trim or deburr the insulator and have it ready to go.

I see how this could be a little issue for people who aren't hands on though.

As for the lathe, (Cleven), I tried to make one out of aluminum, and it failed, so I will have to do like you guys and get my hands on some Teflon stock to turn my own... like you said, maybe a little taller than spec so I don't have to turn so many.

OH! And I do recommend getting a lathe to anyone that doesn't have one. Harbor freight has them for $499 here in the states for those on a budget. A lathe and a 3D printer make for a nice couple

 

[cleven 4]

Tip.

since the ptfe is rather soft, use the tail stock to centre. Then cut the profile with the tailstock centering. Leaving a slight small section at the end near the tail-stock. Then load in an end mill (10mm or so) and cut the end down to size, load another end mill (6mm or so) to cut the room for the tube, Then drill out the center for the filament. I added a profile chamfer to the entrance which for me imrpoved operation. I then cut it a bit longer and placed it in an end mill where I trimmed it to length.

 

[kris 29]

The extruder design needs to be improved in order to reduce the heat flow to the PTFE part. At the moment the component is subjected to too much heat. I am pretty sure there is potential as I have posted in my heat analysis of the setup.

 

[solid-print-3d 30]

The extruder design needs to be improved in order to reduce the heat flow to the PTFE part. At the moment the component is subjected to too much heat. I am pretty sure there is potential as I have posted in my heat analysis of the setup.

 

I agree, but what's more likely to happen in the very near future, Teflon insulators to become disposable items that we can swap out at low cost, or a complete redesign?

I suppose someone could design a liquid cooled, aircraft aluminum insulator, that was coated with Teflon on the inside, anodized on the outside, was good for 5 years, and has an operational range of +400 C ....

 

[3poro 9]

I agree, but what's more likely to happen in the very near future, Teflon insulators to become disposable items that we can swap out at low cost, or a complete redesign?

 

I don't think it's obvious a complete redesign is needed. We'll see, one day

For me the cost of Teflon isolators is not the biggest issue. The bigger problem is - I don't know when it needs to be changed - or even checked for its condition. What's contributing to its failure and how much? Printing temperature? Filament being used? Printing speed? Number of retractions? Also, it's difficult to inspect the Teflon part accurately enough to know whether problems are likely to appear or not. When problems appear, they are nasty to track and they tend to ruin prints when you are least in the mood for debugging.

Another aspect; if the print head was more tolerant for high temperatures, it might help to sort some of the problems now facing dual extrusion. Also, this would allow us to use broader range of materials - see for instance this thread:

http://umforum.ultimaker.com/index.php?/topic/6867-is-there-some-way-hack-to-print-at-270c/

Of course, some people would use the better temperature tolerance to decrease noise level by using less noisy (rear) fan in the print head.

 

[solid-print-3d 30]

@3Poro,

The redesign statement was a response to the comment before mine from Kris.

I still think it would be nice to have a bag of insulators that I could change any time I thought that it might even be REMOTELY contributing to a poor print. At $20 each, there's no way I can afford a bag of them. If it wasn't the cause, I'd just throw it in the bag labeled "used but good".

KNOWING that the insulators WILL fail (I print in ABS mostly), it would just make sense to have this kind of option available, opposed to charging $20 each. I mean REALLY? $20 for a part that's proven to fail anyways? That's all I'm saying...that it be reclassified as a consumable, and priced accordingly.

OK, I'm done beating that dead horse

 

[densohax 0]

How about a ceramic washer for insulation between teflon piece and the brass? It shouldn't cause enough friction to be an issue.

 

I have some ceramic rods, just didn't spend the time to play with my new diamond tooling

I'll let you know if/when my new setup fails.. In the meantime, I'm still very happy using the red ptfe that came with the makerbot thing-o-matic. It prints wonderfully!

 

[Anders Olsson 136]

I have done some experiments with various metal spacer designs lately.

The conclusion so far is that with ABS more or less anything out of metal will work as long as is it kept reasonably cool.

PLA is a completely different story. I kind of consider PLA as the root of all evil after seeing what it does inside the spacer :cry:

It is not so much friction that is the problem, it is the fact that PLA softens into a rubber-like state at very low temperature.

When the filament softens like 10 mm inside the spacer and you put it under pressure, the diameter of the rubbery part will increase.

This forms a very efficient plug, which seals better the more pressure you apply. It gets particularly bad when feeding a hot filament shortly after retraction

This can easily be simulated by feeding a piece of PLA through a 3.1 mm metal pipe, then heating the pipe until the PLA softens and feeding it with the output blocked.

As long as the output is not blocked the PLA passes through even in it's rubbery state. When the output is blocked though, it forms a very strong plug which does not let go when the output is open again.

Pulling the filament with the plug out backwards is easy though.

The teflon spacer solves this problem by having a surface slippery enough to allow pushing the rubbery PLA-plug through the spacer.

I have some ideas for a metal spacer workaround which I will be testing the coming days. It is not an easy thing to fix though, it might not even be possible to solve.

Much easier would be to use the teflon spacer only for PLA and a metal spacer for other high temperature plastics.

This solution is probably not accepted by the 3D-printing community though since people gotten used to being able to print both PLA and ABS with the same setup.

 

[3poro 9]

I have some ideas for a metal spacer workaround which I will be testing the coming days. It is not an easy thing to fix though, it might not even be possible to solve.

Much easier would be to use the teflon spacer only for PLA and a metal spacer for other high temperature plastics.

This solution is probably not accepted by the 3D-printing community though since people gotten used to being able to print both PLA and ABS with the same setup.

 

I'm very interested to hear how your tests will turn out - best of luck with them!

Regarding the idea of different spacers... I'm referring to the discussion over here:

http://umforum.ultimaker.com/index.php?/topic/3803-ultimaker-2-dual-extrusion/

I would accept the idea of using two different spacer materials - but preferably on different extruders, at least as long as they aren't made very simple to change.