PLA Plugs at the end of the Bowden Tube

[ComJak]

Recently, I've run into a weird problem where prints would fail after a few minutes due to under extrusion. Nozzle is clean and cold pulls are always spotless. Extruder gear is clean and extruding without the hotend on is fine. I've noticed that people say that the plug shown herehttps://www.toybuilderlabs.com/blogs/ne ... tfe-insert will cause this problem and it definitely seems to be the case. However, not matter how hard I push that damn tube in while pulling up on the collet, a tiny plug forms. THIS IS WITHOUT RETRACTS ON.

I've tried printing from 230C to 195C and it forms in all situations without retracts. I don't think I can physically push that bastard in any more than it is now and when it's "in", there is no slop when I pull on it. I've tried tapering the end of the ptfe as well with no benefit noticed.

.35 Brass Nozzle
Stock Rostock Max v3 hardware
Hatchbox PLA
60mm/s

Is there something I'm missing?

[mhackney]

Yes, I have had this happen a number of times. I finally completely disassembled my HE280 yesterday. The issue was, for me, that it was very difficult to push the PTFE tube all the way down. It is a very tight fit for my tube. That leaves a small gap and that fills with melted plastic. Increasing temperature and retracts only make it worse. Find a 4mm or so drill, rod, stick and push it into the top of the hotend (no filament) and mark it right where it comes out. Transfer this mark to your Bowden and then make sure you push it down that far. Off my 1mm is not good enough! You might try beveling the end of the tube to help it seat a bit better. I actually reamed out the lower heatbreak piece with rouge to very slightly polish it so the tubing slides in easier.

Also, once you have this happen, the upper part of the Bowden may be deformed where it is held by the black plastic PTC fitting. Cut 5-10 mm off the end so it has a good/fresh section of tube to clamp to.

[IMBoring25]

It's very important that the Bowden tube be cut perpendicular and I've also started chamfering the OD with a pencil sharpener to further reduce the risk of obliquity causing gaps.

[ComJak]

I've tried cutting it as perpendicular as I can. I also did chamfer it with a blade but It was kind of rough.

Can anyone upload a picture of a cold pull through the bowden so I can compare my results?

[Turpinator]

I was struggling with this since I upgraded to the new hotend in oct, eventually i just decided to take it all apart after messing with it, and realized the same thing you did. The bowden tube wasnt fully seating in the heat brake.

To fix this, I tried to chamfer the edges and smooth it off to make it seat better, but it still wouldnt go all the way in. After that, I simply took the entire hotend apart, with the exception of the heating block/nozzle. I threaded everything onto the bowden tube that needed to be. The plastic PCB Cover, the PTC lock clip thing, the PTC fitting, the PCB, and the heat sink. I inserted the bowden tube into the heat brake and then assembled everything onto that, making sure not to pull the bowden tube out. Hasnt clogged in nearly a month, and ive been printing a lot more now, because it hasnt been clogging.

[mhackney]

I ended up using a short 4" piece of tubing I had laying around. As I reassembled the hotend, I made sure this tube was pushed all the way in (using the drill depth method I mention above). This leaves a short piece coming out of the top of the hot end. I attach this to the primary bowden with a 4mm to 4mm PTC coupler (https://www.mcmaster.com/#5225k61/=15pj1nm).

I've been using these for several years to extend bowdens and for a couple of special hot end projects I'm working on. The advantages are:

1) you are darned sure the tube is seated all the way down
2) it eliminates wear and tear on the bowden itself - especially where it passes through the PTC fitting on the top of thehot end
3) it extends the length of your Bowden if you've been nibbling away at it due to 2 above

It does not add any friction or slop and I've never had one separate. These seem to have a lot more reliable and solid attachment to the PTFE tubing than the little black things E3D and HE280 use.

[geneb]

I would also suggest that you slow WAY down. 60mm/sec is way too fast for a .35 nozzle.

g.

[ComJak]

I'm going to keep trying some of these solutions. I've printed many prints at 60mm/s with this exact same setup and it has never really had this problem. I even had retracts out the wazoo. I moved it once across the state and now it has this issue. I'm really confused as to why I had been printing perfect prints before and only now do I get clogs. I'm even sure that back before this past week, I had those PLA plugs in my heat break all the time because when I did a filament change, I would have to trim off the plug. I'm not even 100% convinced that the plugs ARE the issue but from what I've read, the symptoms match so I figure I would give it a shot.

[mhackney]

That's the way 3D printing is. Everything is fine and then some subtle little thing changes and its back to starting with first principles to solve.

There is no way that you could pull the 4mm diameter plug we are talking about up through the bowden tube. You were probably seeing the 2mm diameter "plug" due to the 2mm diameter bore in the hot end. The filament is 1.75mm diameter and the tube is 2mm ID. So that 2mm "plug" created problems too but is normal. Now we are talking about a much larger plug that fills in the gap between the tube and heatbreak. Why did this change? Who knows, the PTFE tube does move/stretch during use, could be that. The black PTC fitting can also lose grip over time for many reasons. Or it could be any other factor.

[ComJak]

Sorry, what I meant to say was, in the past, I had to remove the whole bowden tube WITH the 4mm plug at the end and chop it off in order to change filaments. So I have been printing in the past with the plugs but it had never affected my prints in any way I could tell.

[Jimustanguitar]

I've had this on and off for a long time, and on E3D hotends, too. I've always attributed it to the bowden fitting having some play in the end. Using a locking collar on the fitting also tends to draw the tube up just a touch. It's quite difficult to fully seat the tube AND slide a lock ring onto the fitting without pulling it out just a touch. I can see this happening through the clear front on my EZRStruder, as well.

I've resorted to using my own, shorter lock rings and intentionally pushing the tube in while sliding the lock into the fitting. It takes a time or two to get it right on the end that I can see, so I do that first to get a good feel for what I'm doing on the invisible end inside the aluminum. I suppose that you could set the tube with the top of the HE280 unthreaded ever so slightly, and then thread it into place to take up the slack, but I haven't tried this (and it wouldn't help on an E3D end).

Does anybody else have a magical procedure that they do for this?

[ComJak]

I tried the seemecnc support page solution with the unthreading and threading and it seemed to print smooth to some degree. However, I was afraid to mess something up by looking at the puck so I just left it and kept printing calibration things. After about 5-6 prints, it started sputtering again.

[mhackney]

I basically seat the tube all the way, then pull up the .5-1mm to lift the black lock, insert the lock fitting and then press the tube back in the .5-1mm to fully seat and lock it.

re: E3D full metal hot ends - the issue with the HE280 is that the lower end of the PTFE is hot enough that molten plastic and flow into any gaps that are there. This is what creates the plug. If that zone were always at full temp, that plug would always flow and not be a big problem. But it is in a region where heat creep, long retracts, etc can cause melting and solidifying there - and it is this that causes the problem. The E3D full metal does not have the possibility of a gap in this area, so no plugging. I don't know about their low cost version that is similar to the HE280 with the long PTFE tube.

This is one reason why I'd like to get my hands on a Jet for the HE280, the metal-to-metal junction at the base of the heat break in effect makes it into a full metal hot end and the PTFT tubing end is well above any melt or softening zone. But the Jet has been unobtanium. I have fully characterized the HE280 for my work and will characterize it once I have a Jet to test.

[DerStig]

This is one reason why I'd like to get my hands on a Jet for the HE280, the metal-to-metal junction at the base of the heat break in effect makes it into a full metal hot end and the PTFT tubing end is well above any melt or softening zone. But the Jet has been unobtanium. I have fully characterized the HE280 for my work and will characterize it once I have a Jet to test.

My only concern about the jet is they say its only for hot printing not PLA

[mhackney]

You can most likely print with PLA if you know what you are doing. There is nothing magical about it. I print PLA with E3D full metal hot ends and never have issues. If it turns out to have an issue (hard to imagine) then a similar device but in PTFE would potentially be an alternative. The idea is to eliminate the potential gap that can form.

[DeltaCon]

Does anybody else have a magical procedure that they do for this?

"Sharpen" the end of the PTFE tube a little with a pencil sharpener to get brims off before you push it into the hotend. When you pull-up the tube to get the collar seated, you can push it in again afterwards. The fittings work only going out, not going in.