Living hinge hand?


#1

I hesitated to start this post, but here goes.
I’ve seen many examples of the ‘living hinge’ approach to produce a two dimensional curve, and the extension of that idea with the leather glove that is also linked to in the ‘Amazing leather cut gloves’ elsewhere in the threads.
Noting that a lot of 3Ders are making various versions of mechanical hands, often aimed at kids who have prosthetic needs for such devices, I wondered if those avenues could meet up in a design for a hand that was generated from a flat surface, rather than separate pieces.

Almost origami meets the living hinge ?

I’m not offering any design, just throwing a pebble into the pond.


#2

For a prosthetic, you probably need the 3D shape, the strength that solid plastic will give you, and the range/radius of motion of a pinned/hinged joint. But for other projects I bet you could do something interesting.


#3

Yes, but I had assumed the surface would create the 3D shape by wrapping right round, at least wrist and palm.


#4

I was thinking more about the fingers. You’re right, for the body of the hand (erm) you could get a nice shape.


#5

Made me think of this artist’s work I saw awhile back.


#6

Thanks for the link. It contains some of the images from my posted link, but more.
Food for thought, as they were the sorts of images that would come to mind when mapping the need for bending around the complex surface which our hands have.
I envisage putting on a latex glove, then using a felt tip pen to draw cut lines at right angles to the contours.
Hope that makes sense.


#7

Very interesting idea. I’ve printed over 100 such devices over the past couple of years, and have seen a major switch to include thermoforming flat-printed pieces into complex shapes. I’ve posted photos of this elsewhere in the forums.

The challenge with living hinges is that they tend not to be very durable (at least in my limited experience). While they can flex into shape, continued flexing (like a finger or wrist joint) tends to break them fairly quickly.

Would love to see someone investigate this further (and will likely do so myself later this year).


#8

Thanks dwardio, I take your post as encouraging.

This immediately put polypropylene into my head as a possible material, as one of its characteristics, I believe, is to realign the molecules in places of high and repeated stress, like a hinge joint, so in essence it gets stronger at that point. Hence its use to make plastic boxes with attached hinged lids.
Yes, it will eventually break, but the cost/lifetime might be worth it.


#9

I’m resurrecting this thread as I now have an actual need for something similar.

I need a design that will enable me to use the GF to cut an articulated hand for, guess what ?
To hold a fan as an exhibition piece.
In fact, I’ll need quite a few, so making them is going to be more economic. I’d happily pay for a plans, but for the moment, I’ve not found any likely candidates.

While I could go to Hobby Lobby, or similar, and buy an artist’s model hand, I’m thinking of eventually being able to have it waving the fan, to and fro.

Doing a quick search for a model, took me back to the living hinge style cut leather glove, linked above, so that might be another possibility, or even combining that with some limited rigid skeleton along the lines of the ubiquitous dinosaur model.
Any thoughts anyone ?


#10

I’ve got one I did for a middle school science class, but it kinda sucks :neutral_face:

It was all about the opposing tendons, but there are so many it’s essentially impossible to control. If you wanted it fixed rather than movable it might be OK, but really finger bones and joints are incredibly easy to design if you’re not going for serious anatomical accuracy. (You could do some engraving and extra hole-cutting and make the hands decorative as well.)

(FWIW, my trick was to use three pieces glued together for each “bone” so that the joints were a simple pin hinge supported on each side.)


#11

Thanks, Paul. While I wait for ideas to strike, I found a reasonably priced artist hand on ebay, so I thought I’d buy that in as a starting point.
I’d like to avoid the ‘uncanny valley’ effect, so I think that a sliced section hand would work ok.

I might be able to get away with just wrist movement being motorised, so just friction stiffened joints would work for the fingers.
John