The Importance of a Clean Bowden Tube

The Importance of a Clean Bowden Tube

There is a lot of advice out there on the internet for 3D printer fans. Not the kind that blow, the kind that are people. And don't even go there.


Anyway, the advice is copious and varied and often misleading, obsolete, or just wrong. So how can you tell if it is good advice? One way is to see if you can get several authors to give more or less the same advice. Another is to watch a video of the advisor actually doing the action. One last thing (and this applies to the obsolete bit) is to try and figure out if the advice being given is either very recent or  applies directly to the model thing you are working on (for instance, can you see in the video that the parts being serviced look like the parts on your machine).

One common issue that EVERYONE talks about is nozzle clogs. Also sometimes referred to as Hot End Clogs or perhaps as God Damn Fraking Clogs (GDFC).


Clogs seem to occur at joints where various components of the filament feeding system connect to one  another. They also occur in the constricted areas of the nozzle where tiny impurities in the filament can get stuck and accumulate enough to form a partial blockage. You usually know you have something wrong when your prints start to come out weak. They look OK (perhaps) but when you flex them you find that they appear to be made of cotton candy instead of plastic.

Now comes the part where advice got me into trouble. I am watching this video about the printer I just got (The Ender-3 from Creality) and it shows a common problem where the bowden tube connectors near the extruder stepper engine is not grabbing the bowden tube securely enough. Because of this, each time the Extruder Stepper retracts a little (which is often done when moving the head across a No Print area) the connector moves. This movement implies the bowden tube is moving. So instead of retracting the filament, we are just flexing the bowden tube some. Non Ideal.

And now you are saying, "What is he talking about? What is a Bowden Tube?"

The White tube coming from the back left
to the blue extruder on the left if the Bowden. 
Filament roll is off picture left.

On the open license printers, the filament extruder comes in 2 distinct parts, The Extruder Stepper motor (which pushes a carefully measured amount of filament through the hot end) and the Hot End (which is essentially a precision glue gun). On many machines these two parts connect pretty much directly to each other (this is how it was on my original M3D Mini). On the Ender 3, however, the extruder-stepper motor is fixed in place over on one of the side supports and the Hot End is moving around on the X axis Arm. Between  these two parts is a plastic Tube that channels the still hard plastic filament from the Stepper to the Hot End. This is the Bowden tube. One my Ender 3 it is about a foot long.

So anyway, the advice says that any play in the tubing is a bad thing for print precision and you should fix this situation by getting a high quality Bowden Tube and tube connectors. They are like $7.00 on Amazon. So I got them.

Now, one would think that all one need do is to pull off the old parts and stick in the new parts but this is where I ran into problems. The part of the bowden tube that sticks into the hot end HAS TO push up right against the nozzle. Any space in between these parts leaves a place for hot filament to sneak into and cause blockage and bad prints. This becomes hard to work with because the way the bowden tube latching mechanism works is that you press the tube through the connector and then pull back a little to lock it. This pulling back creates a Gap !!

And my advice guy didn't tell me about this.
This meant that not only were my next many prints bad, but I didn't realize the problem and so was doing normal clog clearing things (like a cold pull) and that was having no impact.

So. I went and did more research. I found a guy warning about the distance between the bowden tube and the hot nozzle. He claims it often comes from the factory with this space problem. How to fix it? Pull off the nozzle and insert the tube and visually confirm that the tube sticks just the tiniest bit out in the threaded area of the nozzle. Now when you put the nozzle back in, it will abut the tube and you won't get leaks.

See what I just did there? I gave you advice without the appropriate warnings:

1. Never remove or tighten your nozzle unless you have preheated the head to PLA (200C)
1. this turns out to be a biggie. Who Knew?
2. Don't put your skin against anything preheated to 200C.
1. This is an even bigger biggie. Especially for us Americans used to Fahrenheit.
3. Make sure the Hot End track is cleared of Gunk before you put in the Tube and Nozzle.
1. How? I did it by taking a small extra piece of tube (6 inches) and pushing it all the way through the hot end with the end HOT. It pushed out a huge glob of gunk.
2. Be careful, your piece of tube will heat up quickly. Perhaps wear gloves for this.

Want some more Bowden Tube Advice?

Every once in a while you will get a hunk of plastic stuck in the tube. Right at the end where the tube is hot and the filament melted in it and made a clog. You usually get rid of this by cutting off the end. Many people say, don't snip it with your filament cutters as this will bend the tubing. Other people just go ahead and clip it and don't seem a bit concerned. A third guy says to ether buy the special Bowden Tube cutter, or use a very sharp cutting tool, like razor. That is what I did, I used the blade of a box cutter. 

Does having the new Bowden Tube and the new attachment mechanisms that don't slide matter? 

Maybe.

A little.

But certainly not worth the hassle.

On the other hand. Look how much I learned.....

And now, future Me, gives some even more useful information. Go onto Thingiverse and look around for some Your Machine Specific hot end additions (try here). Essentially, there are measurement devices (yes, you could use a tape measure) and a little gasket that allow you to cut a short piece of bowden tube material and fit it into you printer between the nozzle and the bowden tube attachment fitting. This provides a specifically measured piece of tubing such that you won't ever have that leaking gap again. Work great. Less filling. 

I also have the answer to the question of "Why have  Bowden tube at all?". That is, why not put the extruder right at the hot end and avoid that long path? It is a tradeoff. Putting the extruder right at the hot end (which is called a direct drive extruder) does make for really nice well constrained filament path. It allows you to print flexible, like TPU, and it seems to give very exact control over PETG and PLA (which can make less threading and such). However, it puts more weight and strain out on your moving arms. Which means you may need to move your arms Slower to avoid inertia fracking with you. The direct drive mechanism is also a bit harder to load.  However, that said, I put a direct drive onto my Ender-3 and I love it. (I still have the Bowden on my larger CR10).

Even more Future Me says: Hey, I just put the Micro Swiss NG Direct Drive Extruder on to my CR10 V2 and it appears to work great. The advice to slow the X-axis moves down a little seems to be needed, however.