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Bowden shrunk at hot side (or maybe always just smaller)

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Today I disassembled my hot end on suspicion of plugging. It wasn't completely blocked (plug would melt when heated) but the print extrusion performance was lowered which made me suspicious.

Long story short, I also had the opportunity to measure that end of the bowden. I found that it is pretty close on the mark on 3mm, not quite 3.1mm without some pressure on the calipers and definitely nowhere near 3.2mm.

I'm wondering whether the bowden has shrunk or something else gone awry? I'm printing owen's bowden clamp now, so I know that the diameter has definitely not been reduced due to any clamping as such because it has never been clamped. Well aside from that white collar thing.

I have always felt that borderline 3mm+ filament segments would get pretty tight towards the hot end side of the bowden, but I always chalked this down to the fact that there's more filament in the bowden and further down the bend when the filament reached that position.

Is this actually normal? I always thought that the '3mm' filament must have been 2.89 nominal (as the included roll I was delivered was such) but now that I've been able to try out more filaments from different suppliers I'm having my suspicions that this is not the case (and I have read since that the ID is meant to be 3.175mm nominal or 1/8ths of an inch).

It's probably like the last 8cm of my bowden that seems to be tighter - the rest of it is ok.

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Yes, I have tested it more with a filament that had a slightly larger head and I detected that it was more like 5mm where there's a contraction near the hot end.

I forcibly made the contracted end larger at the tip, seems that the tube was probably not supplied faulty and it might be something to do with heat softening the tube and pressure crushing it.

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i got a new one from UM. it measured 3.2mm ID.

I put it in the PEEK, printed for a couple of hours, then dismantled to inspect it.

the ID was now 3.1mm.

it shrinks, probably due to the OD being slightly larger than the ID of the PEEK so the material has to go somewhere and heat softens and reforms it to the new size? dunno, but it happens.

whatever you do, don't try to enlarge it. you'll create plugs. i already tried that.. :(

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