Friday, 20 November 2009

Beefed up bracket

When I started reversing my extruder I noticed the motor bracket flexing. Here is a short video showing it in operation: -

BendyExtruder from Nop Head on Vimeo.

It was immediately apparent that I had not made it strong enough.

As the worm gear is about twice the diameter of the threaded pulley the axial force on the motor is about half the force required to push the filament, i.e. a few kilograms. After making a few objects it cracked along the layer where the bearing housing rises out of the flat motor mount.

I designed a new bracket but I was back in a chicken and egg situation with no working extruder to print it. As Erik pointed out you need a Robin Hood / Friar Tuck strategy of having two machines so that one can make replacement parts for the other. I must get my Darwin up and running!

In the meantime I cobbled it back together with some random bits of metal, some tiny G-clamps and tie wraps: -

I made some of the new bracket thicker where I could: 8mm instead of 5mm, which should be ~2.5 times stronger. I also added some ribs and extruded it at 10°C higher temperature.

This one seems solid as a rock, but it did warp a little more. The stronger you make something the more it warps.

Here is a video of it not flexing: -


  1. Ya, you need support on the sides or the top. Like gussets. Great to see a vid of what is really going on. Better than reading text describing it. Love the work you've done. Wish school didn't consume me otherwise I would build one myself. Still want to, just need to finish Electronics Engineering Technician course first. The mechanics is easy for me. First things first.

  2. heh, I love that pair of viruses!

    I'm in a similar position though - I've got a second Darwin all set to go, but no working extruder for it. I try to keep a spare set of parts around, but I keep using them for experiments.

    Are those parts made from PLA? They look good! Would you mind posting your design files? I'd love to see how you designed them in CoCreate; I'm finding the built in tutorials a bit sparse.

  3. Nophead,

    you posted numerous extruders you made on your blog. Did they *all* break?

  4. The movement looks fairly significant, so did you find that you needed to re-tune the reversing mode of the extruder feed to accomodate the stiffer bracket?

  5. Nophead,

    I think I finally know what the problem is with reversing that we had. I just bumped into it again myself. If you do not push the filament forward much, but do have a lot of short segments with reversing (our oozetest objects especially), you pull back hot filament higher in the extrusion nozzle, where it will warm the heater barrel up. When you push it down again, the colder filament above it will start heating up from this higher section of the heater barrel.

    My 3D-to-5D-gcode.php script (which does many things, including decide when to pullback) will now pull back only when it's a minimum distance to where the head is traveling. Otherwise the amount of ooze is minimal anyway and the build speed is reduced too much. I will put another constraint on this, minimum extrusion before pullback.

  6. Hi Nophead,

    That part being printed looked familiar....

    Keep up the brillaint work!!

  7. @Dan,
    The reason for the complicated shape and unequal ribs is to allow screwdriver access to all the screws.

    PM me you email and I will send you the CoCreate file. It doesn't really help to show how I made it because, unlike AOI, there are no construction items, just the finished objects. You don't need to keep anything because you can edit the 3D objects directly. E.g. move faces, change radii, etc. E.g. to make clearance for the gear I subtract it from the motor bracket and then increase the radius of the carved out shape and moved the side faces outwards.

    I often create workplanes on faces and then project construction lines onto them from the 3D geometry. I then add new features to the face by extruding or milling.

    Of the ones I have used they have all broken down at some point. I retired my "New Year Extruder" because it can't reverse so is no longer compatible with HydraRaptor. It also needs a fan to work with PLA.

    The "Fast Extruder" is not physically compatible with HydraRaptor's mounting bracket so I will use it on my Darwin. I don't have any other complete extruders.

    I increased the pull-back from 0.5mm to 0.75mm as the bracket started to flex more. I haven't reduced it again. I might be able to get away with less now, good point.

    I don't think pulling back is a problem on this extruder. It is only 0.75mm and doesn't accumulate so it won't move heat much further up the barrel. A good idea to not pull back when moving very short distances but other than wasting time it doesn't seem to be a problem.

  8. Meccano gears are well cool.

  9. I'd also spotted those were meccano gears, been thinking of getting a meccano worm gear for one of my projects

  10. dude!

    now we want a "after"-film!!


  11. Dude common! let us see how it worked out! Less flex?? //Swe

  12. There was no noticeable flex so it won't be a very exciting video. Next time I build something I will video it not moving.

  13. OK Anon from Sweden, as promised I added a video of the new bracket not flexing.