Push In Fittings Frustration!

I swear I’m dumb, but I can get the fitting onto the tube, but any time I need to move it down…nope! It’ll move further up the tube but not down.

grumble grumble grumble

I had one pish in fitting that found its way to push out. The locking collar inside it somehow broke, so the ptfe tube wouldnt stay put.

But yeah, they can at tines not be very co-operative.

By the fitting, you mean the brass pieces that either go on the hot end or on the extruder? If that’s the case, you’re not dumb. They contain small metal teeth slanted at an angle. If you push the tubing into the fitting, the teeth are pushed down and out of the way, but if you try to move the tubing out of the fitting, the teeth dig into the tube and are pulled up, digging in even more.

That’s by design.

At the hot end, the Bowden tube must go all the way down and contact the top of the nozzle, producing a continuous path for the filament with no gaps. If a gap exists, filament will ooze into it which, at best, prevents the filament from being retracted properly, and at worst, starts to ooze out of the sides of the hot-end, between the cracks, and can completely jam it up.

At the extruder end, the extruder applies quite a bit of force to the filament in order to force it out a nozzle that may be as small as 0.2mm in diameter. That creates a lot of back-pressure which, because the Bowden tube is inevitably curved, applies pressure to the sides of the walls of the tube. That pressure will try to pop the tube out of the extruder fitting if the teeth didn’t engage it and hold it in.

In a theoretically perfect world, where the Bowden tube never degrades, you would never have to pull it up out of the fittings (or push the fittings down the tube, depending on your perspective). This is why, when you bought the machine, you likely received one extra fitting for each end, since, if the tube becomes damaged and needs to be replaced, you’re pretty much sacrificing the fitting at the same time. You could try and force the fitting out. This is especially easy at the hot end where the tubing is designed to pass right through the fitting - you cut the old tube, unscrew the fitting and pull the old tube out of it from the hot end side. Put the fitting back in and push in a new tube. At the extruder end, however, the fitting is narrow at one end so the tube goes in but never out.

Just have a few spares on hand for when you need to replace the bowden tube.

Yeah I usually end up pushing the fitting up the tube, trim the tube ad nauseum until my bowden tube gets too short to reach all the way to the other side of the plate. Luckily I did think to buy extras in case of whatever.