Finished prosthesis and review of project

by on Nov.07, 2010, under Prosthesis

I have done the final steps in making the prosthesis suitable for use on a bike.  I put a CB antenna mirror mount bracket on the end, which is suitable for bolting to something round.  To allow for a quick disconnect of the socket I used a clevis pin and secure that with a hitch pin clamp (cotter pin).  I wanted a turnbuckle for the wrist which gives me pronation and supination, or rotating of the wrist.  This allows me some freedom of movement that a fixed connection would not.  To allow for bending of the wrist I did not want the turnbuckle attached to the CB antenna mirror mount bracket without something like the clevis pin.

The hole in a standard CB mirror mount bracket is 1/2 inch in diameter, however my turnbuckle which was chosen for its overall length was too small for the clevis pin to fit through.  I had to spread the loop of the turnbuckle to make this fit.  In doing so I felt that the loop of the turnbuckle was too open and that it could become separated from the clevis pin too easily.  To remedy this problem I pulled out my welding rig (GMAW) and welded the loop of the turnbuckle to the clevis pin.  I am not the best welder but I think that the weld is solid and think that it does not look terrible.  For illustration purposes I painted the CB antenna mirror mount bracket red which allows it to be identified easier.  Since there is minor rubbing the paint will come off soon enough, so I do not think painting is a suitable solution. (continue reading…)

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Carbon fiber and painting

by on Oct.29, 2010, under Prosthesis

I decided to take the bottle socket I made and layer on some carbon fiber for strength.  This made the socket much more rigid and able to withstand more static loading.  I did not like the way the carbon fiber looked so I painted it.  I thought I had a can of black but I was mistaken, my choices were red or blue.  I opted for blue.

The socket is pretty much done, the only thing that remains now is attaching things to it to make it useful.  Since this is my second socket ever and the first one that has worked reasonably well I decided to complete it as much as possible.  I will likely make additional sockets, especially since they cost a couple dollars each to make.  (continue reading…)

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Creating the socket

by on Oct.27, 2010, under Prosthesis

I was trying to shape a sheet of acrylic that I got at a larger home improvement warehouse store, and was having difficulties.  First I tried to use a heat gun.  This was mildly successful but it took a lot of time to shape the plastic and ultimately did not work that well.  Then I tried an electric griddle that I had for other non-food projects.  This was much more successful, I could get the plastic soft by heating it to 250-300° F.  I was able to shape the plastic a bit until it cooled.  This griddle, which is fairly inexpensive, did not have a uniform temperature across it so some areas would overheat and bubbles would form and other areas would still be harder.

The weekend came and I went to my friends house, while there I went to the local store and picked up a giant cookie sheet thinking I could bake the acrylic on that.  At the end of the weekend I came home and in my inbox was an email from a prosthetist that I had been talking to about my endeavors.  He gave me a youtube url which made things so much easier for me. (continue reading…)

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Making a positive from a negative

by on Oct.20, 2010, under Prosthesis

After making a negative mold of my arm, the next step was to make a positive.  The first step was to coat the inside of the mold with a release agent.  I used Vasoline brand petroleum jelly (it was the cheapest available).  This has a high success rate with plaster casting.   In order to apply it thinly but everywhere I used my heat gun on a setting of 750F and melted a little on the top, taking care to not melt the plastic jar that contains the petroleum jelly.  I then poured the liquid jelly into the mold and rolled the mold around to coat it.  I finished with some softened (warm) jelly and a sponge paint brush.  I then made a suitable stand to hold the mold upright, as you can see from the photo this was nothing more than a roll of duct tape, which worked well for my casting.

Next I mixed 1 part water to 2 parts plaster of paris. This results in a liquid paste, not unlike runny oatmeal.  Start with the water, then add the powder, when you have added all the powder stir until no lumps are present.  By adding cooler water I had a longer time to work with it before it would start to set, which meant I could completely stir it with a wooden paint mixing stick.  Once fully mixed I poured it into the mold slowly allowing air to escape so no bubbles would be trapped.   You may need to gently tap the mold to get air bubbles to work their way to the surface, the liquid state of the plaster should allow this to happen. (continue reading…)

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Casting for the prosthesis

by on Oct.19, 2010, under Prosthesis

As some of you are aware I was born with only one hand.  I am missing my right hand, wrist and about 1/3 of my forearm.  As a child I wore a prosthesis, a pincer thing I called an alligator, a hook, both of which are not nice when you are 6, and a hand.  I got my first hand at  the age of 9 or 10 and another at the age of 18.  Both were the Otto Bock style hands, complete with the cosmetic glove.  There are severe limitations to these hands as there is no wrist movement save a manual rotation.  This makes it difficult to do many tasks because bending your wrist is somewhat important.    Another limitation of the standard hand is its grip, or lack of grip.  Only the thumb, index and middle finger moves or provides any grip.  There is a cosmetic ring and pinky but they offer no support in gripping or manipulating tasks.  Because the curve of the gripping fingers is fixed you can not grasp small items like a chisel or many hammers and use them in any meaningful way.

There are companies that make better prosthetic hands, Touch Bionics for example has some fairly impressive looking hands.  The problem with those is that they are expensive.  The pulse would be my hand of choice at the moment.  My medical plan, which is paid for from the Indian tribe that I am a member of, does not cover them.  Being a cheap but determined individual I decided to make my own.  (continue reading…)

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