Sunday 7 October 2007

Brush off

HydraRaptor was using a knife to remove excess filament from the extruder :-

It always cut the filament OK, but it was random whether the loose bit fell off or stuck to the far side of the nozzle. The soundtrack of a video I saw of a commercial FDM machine said that they use a brush. I thought I would need a wire brush for 200°C but then I reasoned that, if the nozzle passed through fast enough, the high specific heat capacity of plastic might mean that it would not have time to melt. I decide to give it a try with an old electric toothbrush head :-

It does seem to work quite well. Here is a video of it in action :-

The scrap of filament sometimes stays stuck to the brush but subsequent passes eventually knock it off.

When I was using HydraRaptor for milling I had a tray around the table and a plastic skirt to protect the mechanism of the precious XY table from loose plastic chips. When I moved on to FDM I thought these would not be needed because it is a lot less messy. Actually I was wrong as HDPE chips are appearing, presumable from inside the extruder, and the filament offcuts sometimes ping off from the brush. I have therefore refitted the tray and skirt.


  1. LOL! Looks like your brush is a recycled Braun electric toothbrush head. I guess I'm going to have to start saving mine.

    Mind, I had a bunch of 'em six months ago but tossed them when I cleaned my flat after my son decamped for university last month. :-(

  2. Yes it is an old Braun head. Something a bit stiffer, like an old fashioned manual toothbrush might be better.

    I also think the knife could be made to work by mounting it at the top of a thin deep slot. That would stop the offcut swinging upwards and sticking to the nozzle.

  3. I tend to put a tab on my prints where I start the extruder running and then extrude up to the actual print. That way, if it doesn't start exactly where the actual print begins it's no big loss. Also, squiggles like you are trying to cut off cause no trouble if they are at the beginning of a tab. The tab gets cut off in any case.

  4. Hi nophead,

    Nice to see this - I'm just at that stage now. Gonna try a blade and brush combo.

    Hope the new nozzle-wipe code is useful to you? I'm a beginner on Java so would appreciate any feedback...

  5. Hi eD,
    The code might be useful to me in the future when I get to grips with the host code but at the moment I just control my machine with Python script. I am also a Java novice: C, C++ and Python are my languages of choice.

    The brush worked well until I upped the temperature to 240C, at which point it starts to melt a bit so it is slowly wearing away. A wire brush may work better.

    I think I will try a blade again next but this time mount it in a slot. When you slice the filament off it quite often swings upwards and sticks to the nozzle. An edge opposing the blade would stop that happening I think.