You might have heard about the 3D-printed prosthetic hands created by Richard Van As and Ivan Owen for about 100 children thus far. That's a great thing they've been doing. There's also a "Snap-Together Robohand" version, http://www.thingiverse.com/thing:92937, which is intended to be easier to build.  I'm sure it is... but it still takes half a day to print the parts and assemble them.  Unfortunately, I had less than 3 hours total on Saturday, September 28, 2013, to give an overview of making technologies and have YMCA Black Achievers students actually build something. So, I designed a new prosthetic/robotic hand for which all the printed parts print assembled without supports in less than an hour.  You still have to thread some fishing line and rubber bands through it, but from print start to working hand is easily done in less than 90 minutes!

The hand is roughly sized to match that of a 18 month old girl. It embodies a variety of compromises, any of which might make it unusable as a prosthetic in practice...  but it certainly is functional enough to get the idea across -- which was my goal.  I know very little about prosthetics, but I do know that fitting them is a very personal thing, so the primary design doesn't have a mount attached. It is possible to add a simple mount and still have the complete structure print assembled as either a prosthetic hand or a hand for a robot.

Step 1: It Prints Assembled (but you still need to add some stuff)

Although the structure of the hand prints fully assembled, you still need to add the stuff that makes it able to grasp things. It doesn't take much time, nor equipment, but here's what you'll need to build a fully operational hand:
  • A 3D printer and printing supplies. I used a MakerGear M2, which is an excellent printer, but as I write this costs close to $1,800... there are many cheaper alternatives, and at least some of them can make prints as good as those made by our M2. This hand should be printable on just about any FDM/FFF printer with a large enough bed. Printing one hand uses less than $1 worth of PLA filament. We recommend PLA, rather than ABS, because PLA is more dimensionally stable and there are various spots where a little warping could cause a lot of problems.
  • Five rubber bands. We need the fingers to be able to return to and stay in the open hand position, and these wide rubber bands do that pretty well. You can buy a bag of "firm stretch" ones for a $1 if you haven't got them already.
  • A few feet of monofilament fishing line. The channels for the fishing line form paths accepting wires or line up to about 0.7mm diameter; I used a 20-pound-test line with a 0.0185" diameter, which is a little less than 0.5mm. One could use string, etc., but different plastics tend to move past each other more smoothly without needing lubrication. A 250-yard spool costs less than $3 and will make a couple of hundred hands.
  • A pair of scissors. This is used to cut the rubber bands and the fishing line.
  • A pair of tweezers with a very fine point. This is used to guide the rubber bands through the slots. The end of a partly-unbent paper clip is actually a good alternative.
Yeah, that 3D printer is a bit expensive... if you don't own one, it's time to find a friend who does. Everything else you very likely have around the house.
<p>Can I print it with ABS plastic instead of PLA?</p><p>(I am using a come3D printer based on Thing-o-matic)</p>
<p>Also, can u kindly send me a single left hand model file?</p><p>My email is <em>jordanfung2002 [at] gmail.com</em></p>
Excellent! Good luck in the competition!

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Bio: I'm an Electrical and Computer Engineering Professor at the University of Kentucky. I'm probably best known for things I've done involving Linux ... More »
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