Tuesday, May 06, 2008


Open sesame...

...using a reprapped door handle.

This was printed on top of the latest mod to my Darwin, which I recommend as it
  1. Is simple to add, and
  2. Saves lots of messing about with the Z-axis screw drives and zeroing.
It is a Z Bed. It consists of a piece of MDF held down by three (not four) screws and nuts. Between it and the bottom bed round each screw are some stiffish springs. With this, it becomes trivial to set up the Z=0 position so that it's exactly the same distance under the extrude head just by eye. You move the head about, adjusting the Z Bed's pitch and roll until it comes out right.

The trick, of course, is not to raise the Z Bed too high; then the head doesn't collide with it when you're moving the head about. Being cleverer than I, you should be able to manage that...

This is just a little test one. I shall replace it with a piece almost as big as the base below it. It'll have two screws in the front corners, and one in the middle at the back.

Oh. And now we can go out to the scullery:

Reprapped door handle from Adrian Bowyer on Vimeo.

(Well. We could before. But not using a cool reprapped door handle...)

To get the door handle design, see the RepRap objects library here.

Brilliant! Why don't you do the rest of the door hardware assembly before you take on the scullery? having a complete doorknob hardware assembly and a set of proper hinges would be very, very attractive in Africa from my experience. :-)
I tried a hinge using PCL (which is very tough and flexible), with a thin section forming the actual hinge. That worked fine, but the thicker bits that attached to the door and frame were also a bit too flexible, and so bent and the door didn't hang right. I couldn't make them any thicker to strengthen them as there was not enough gap between the door and its frame.

More thought needed...
RepRap is really opening the door to innovation.
awesome! i'm loving all these printed parts. if only i had a solid week alone with my machine. i know i'd be printing in no time!
How about HDPE instead of PCL for the hinge?
@nophead & adrian:

The traditional material for living hinges is polypropylene.

It's not toughness per se that you need in a living hinge, but fatigue resistance.

I realize polypropylene has a higher melting point, but it has so many other nice properties (especially dishwasher safeness) that it might be worth trying at some point.

You might also want to look into a design with some sort of fiber reinforcement: my first thought is postal twine. Even polypropylene living hinges wear out fairly quickly.

Last: I expect fire safety will be an issue with door hardware. If your handle melts away and leaves an opening, the door won't stop a fire the way it's designed to; doubly so for hinges.
about fire safety: It may be harder to get out but at least you won't burn your hands on the handle trying to escape :S

Yes, I'm a positive thinker.
I've been following this project with interest for some time - I think it's fascinating. I'm curious - what is the consistency/flexibility/brittleness of the plastic you usually use? Is there an everyday object you could compare it to? How does it feel?
I give it a week before someone's wife complains that all of the nice, shiney things in the house are gradually being replaced by off-white knobbly things!
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