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Sunday, October 21, 2012

Filament plug, hot head and the short bowden tube

Get rid of a plastic plug in an early Ultimaker V2-like hot end

Updated: check my alternate blind rivet nut setup, it is way more robust.

Shortly after I changed the small bowden tube between the two plates of my V2-like hot end, I made the mistake to cut it a bit too short. Well, I did not try to find a place that would specify this the length, given that my head was not designed by Ultimaker in the first place -- I think.

The problem was that this small bowden tube was not pressed firmly downwards against the peek by the screwed stop brass connector, and it soon resulted in a nasty plug (zoom on the picture for details, check this post by Daid & Technicality)...

It came after I overfed the head with a badly tuned filament feeder (see further posts for the feeder). Actually the plastic still continued to flow but it was way harder... then I realized that some plastic poured out of the bowden just above the peek insulator and melted/solidified all around the white plastic plug, making the flow much harder indeed.

This white plastic clip at the bottom is a bit weird, because it embeds some metallic wire to help locking the tube in place. With melted plastic all around I just could not remove it properly (even by heating it like hell!). So I eventually destroyed it with small pliers.

A spare white clip was nicely provided on the aluminium plate anyway (on the left in the picture), but I did not use it either and instead re-used the destroyed/shortened one mostly because I want to know if it's really useful. Now I know it does not seem to make a difference (see below though)!

Update: check how I got rid of the issue with a blind rivet nut.

Actually, after cleaning up the mess, I put the half-destroyed white connector back in place, just so that the bowden tube could not slide laterally (see next picture for the result).

Automotive blue silicon for sealing the bowden tube to the peek

One improvement I did is this : I added automotive blue silicon gasket maker on the peek. I know it handles high temperatures easily, and it is made against leaks. It is also very elastic when dry so when pressed against the aluminium plate, it should seal the whole nicely, exactly what I want.

Update: better use the "gold" variation of this joint, or double check the temperature. Mine was a bit soft when checked at full temperature (would it still prevent leaks ? I think so).

Make sure not to have some silicone within the tube, I don't know how how well it would flow though the nozzle once solidified... To reduce this risk, I did not wait very long for the silicon to dry before extruding some filament so that any excess would be dragged away.

For now this seems to work fine, even though the white clip no more maintains the short bowden tube vertically. I chose a length so that the top brass connector does push it downwards really hard though.

One last improvement would be to add a stiff tube around or along just to avoid bending the secondary bowden tube; in my case it is really at the limit and I get a slight friction as a consequence. But I do not want more plug like this ;)

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