[Bil’s] Quest For A Lost Finger: Episode I

Casting a hand part 1

A little over a year ago I had a semi-gruesome accident; I stepped off of a ladder and I caught my wedding ring on a nail head. It literally stripped the finger off the bone. This was in spite of me being a safety-freak and having lived a whole second life doing emergency medicine and working in trauma centers and the like. I do have trauma center mentality which means, among other things, that I know you can’t wind the clock back.

hand9A few seconds make an incredible differences in people’s lives. Knowing that it couldn’t be undone, I stayed relaxed and in the end I have to say I had a good time that day as I worked my way through the system (I ended  up in a Philadelphia trauma center with a nearby hand specialist) as I was usually the funniest guy in the room. Truth be told they ask incredibly straight questions like”are you right handed?”  “Well I am NOW”.

So now I could really use a bit of a body hack, having seen the X-Finger on Hackaday long before I knew that I would one day work with them, I was hoping that we could get one to work for me. In speaking with a couple of the mechanical engineers on the Hackaday staff we decided to get [James Hobson] and [Rich Bremer] involved and that the best way to do it was to get a casting of my injured hand out to them.


Starting with casting alginate I mixed it 1:1.5 by volume with warm tap water and mixed.  I had a backup amount ready to go in case I ran short, which it turned out that I did indeed need. Since one hand was now ensconced in gooey mold making stuff I had to use a drill with stirring rod to quickly mix up the rest.

The alginate sets within 12-15 minutes and because it has a little “give” to it I was able to squeeze my hand out without damaging the mold.

Next a mix of casting plaster is made per the instructions and poured in being careful not to trap bubbles.

Cutting out the casted hand was a matter of a single edge razor blade and the cast was complete and ready to be shipped to the mechanical guys.

With the hand cast is on its way to [James Hobson] for his evaluation with an eye towards mechanical design, look for a followup Part II post of his initial assessment of my hand sans finger.  We have discussed making the mechanical finger replacement a Hackaday project and getting input from viewers at large. Are any of you interested in taking part in the process? If so please leave a comment below.

89 thoughts on “[Bil’s] Quest For A Lost Finger: Episode I

  1. Bil, marriage costs us more than our fingers sometimes.
    I usually view the ring finger as an accessory grasper. It usually works in conjunction with the middle and ring. Typing would be the main limitation I imagine. What have you noticed?
    Yes, I am interested in helping with this project.

    1. Would James ir Rich be able to scan the cast to make an stl?
      (Meant to say middle and little above)
      Working on fixing the comments section would be another worthy project. (Editability, unflagable)

  2. I’ve always wondered about these thing happening. I worry about one day having a ring on, as in the past with a high school ring I had an accident that resulted in my losing 1/3 of the skin on my palm.

    Now to only convince the fiance of a suitable substitute to an actual ring. As an atheist couple, rings are almost weird backwards concepts.

    1. Me and my wife are both as atheist as it gets and have never ever had the association that wedding rings could be a religious concept. A quick web search tells me the egyptians invented them, and they have been used throughout time with both religious and non-religious backgrounds, always symbolizing some kind of connection.

      I have to add that I never wore any jewelry before, as it annoyed the hell out of me. Surprisingly, this doesn’t apply for my wedding ring. I couldn’t have imagined before, but I now wear it constantly.

      1. Evidence that most atheists are really pretty ignorant. At least learn about the thing you claim to hate! Sometimes I think people claim to be atheist just because they are too lazy to read and be informed. Seems to be a common thing lately: High opinion, low information.


        Depending on the source, there are varying reasons for rings. In most modern traditions, it typically goes back to the practice of dowry. A form of payment to the families for marrying their daughter. If you tired of her and sent her back to her family, it was compensation for having to raise the spinster (since they couldn’t re-marry.) Hence the reason for it being precious metals and jewels, the usual tradition of being two months salary, and the concept that the divorced wife keep the rings.

        In the bible, you were considered married when you laid down with the person. That’s really all it took. The rest was simply traditions, not religion itself.

        1. One person saying they did a quick google search is an example of most atheists being ignorant? Also odd that you think all atheists hate… actually I’m not sure here since you don’t specify, I’m assuming you mean religion though since it’s mentioned in the post and it’s a common assumption (one which isn’t actually true either)

          Also the practice of a dowry goes back to when women were considered property, you were buying the wife off of her family, not compensating them if you broke up. The tradition might have changed over time (although I’ve never heard the idea of it being to compensate the family if the couple split up), but I’ve never heard of the ring being considered a dowry, it was always in addition to the dowry

  3. One of the benefits of being a single looser never have to worry about ring accidents. Seen way too many accidents involving jewelry and either moving objects or high power to every wear anything while working.

        1. In some countries (or people from German decent) it is traditional to wear your wedding ring on your right hand, as left hand indicates you WANT to be married, while right indicate you ARE. Same goes for pinky rings declaring want/have power.

  4. I’d be interested in helping. I’ve previously worked at the Yale Grablab, who do research into dextrous robotic manipulator design – especially prosthetic hands. I have some experience in mechatronic design and fabrication for grippers and a few contacts with domain specialists who might also be interested in assisting.

      1. Waterjet, DainBramage1991—

        All Metals, she has tried titanium, pure gold, pure silver, surgical steel, etc etc etc. The only thing we haven’t tried is platinum — and probably never will ;)

        On the rare occasions she wants to wear earrings she applies a very heavy coat of clear nail polish and then she can wear them for an hour or two tops. Everything else begins irritating her skin (it becomes red and inflamed) after 20 min or so.

        1. If you get the opportunity, try palladium – I react to pretty much everything (thankfully not titanium, so I can at least wear a watch) and because of that we had our wedding rings done in palladium instead, and after over 1 year of near constant use, no problems so far!

  5. After hearing so many similar stories (my uncle is a carpenter/contractor) this is precisely why I don’t wear a wedding ring. Luckily my wife is very understanding on this subject.

    1. Same here. Only, my wife is NOT so understanding. I tell her that I can take it off when I’m working and wear it when I’m not OR wear it when I’m working once and never wear it again because there won’t be enough finger to keep it on.

      1. There’s the option of having it hanging from a chain around the neck to avoid this kind of catching. Still has cases where you might have issues, but if you’ve tucked it under your shirt you’re usually going to be ok

  6. I was looking around at a tool website the other day and there was an ad for this silicone or rubber wedding ring for high risk occupations, don’t know much about it but after hearing more stories like this I may be getting one for myself.


    I am in no way affiliated with them, just thought others might like a heads up.

  7. iirc, its possable to bind a tendon to coral.
    Human fingers use 3 tendons, two of them are for curling and one is use for straightening. When I was studying the hand I fully expected 4, nature just dosn’t build like we do.
    There are a few robotic hands that use anatomically correct tendon mechanisms you can take info from looking at.

      1. You can also use the sympatheic motion of the neighboring fingers, since the tendons are all connected internally and coupled. I’d recommend using some spectra line in a network to transmit motion from the outer (distal) joints of the neighboring fingers into a proportional motion for the missing finger link.


        1. If I had an electro-mechanical finger the thought crossed my mind to have it decide to curl based on its neighbors, kind of a crowd-decision for the intermediate and distal joints.

          1. Hi Bil,

            This could be done mechanically or electromechanically. At the Grab lab we did a bunch of work using pulley trees and internal linkages to do load balancing across multiple robot fingers. You could build a glove-like device that used a whippletree or similar to kinematically join the missing link and the two neighbors in a dynamic fashion. We have had great success with this approach: have a look at the SDM hand developed by Aaron Dollar (head of the Grab lab) as an example. Joe Belter has been working on adapting this technology for prosthetic whole-hand applications. I see no reason why we could not 3D print a worn device that implements the same system on a smaller scale.

            You could also do this with servo power if you were prepared to carry more weight around, but experience tells me that the minimum extra weight on the hand, the better. Weirdly, a prosthetic needs to be about half the weight of the original body part in order to feel comfortable to a user.

            I’d love to be involved in this project! Feel free to get in touch: paul.pounds@gmail.com or paul.pounds@uq.edu.au


          2. If you are going with a glove, the dirt simple solution is to sew stumpy’s glove finger to the other two, add some stuffing to the stumpy glove finger and go for the ice cubes. Next step up from that is to add joints to the stumpy glove finger. Above that, it can get like the first approach “Tony Stark” took with the Ironman suits. A different one for each job. Doing electrical work? How about a voltmeter, solder dispenser, tweezers, LED light, thermometer or a field strength meter?
            My personal favorite thought is a Bluetooth headset just because of the image of answering the phone with your finger.
            Categories of prosthetic fingers:
            Tool based
            Traditional mechanical (use a different joint motion to power the prosthesis)
            Electric/Servo based
            Posable (bend it to the shape you want, then lock in place)

          3. Thinking about this a little more (and depending on the amount of strength/range/control of motion in your remaining finger), you could run a spectra line cable from the top side of the medial link of the neighboring fingers, inverted through a common pull bar that then tugs on the base of the replacement medial link. That means that when the two fingers close, they’ll pull the artificial finger along with it; if only one closes, the new finger will move only half as much. It’s unpowered, but it will help stabilise grasps and can be made very simple and compact.

            It’s also a reasonable approximation of what the natural tendon motions are doing. Try holding your good hand’s fingers straight and then moving the middle finger in isolation – you’ll see the ring finger move sympathetically. Likewise, if you move the little finger in isolation, the ring finger will likewise move.

  8. I saw a story about a guy who grew his finger back by putting a processed pig bladder cell lattice on it until it healed completely with original finger print and nerve-endings. The show was worlds strangest and I believe it was the Inventions episode on the Science channel. they are conducting clinical trials on I.E.D. victims with high success. who knows you may be able to regrow your own.

  9. Thanks everyone, with y’alls permission I would like to email those that said they were able to give a hand (sic)

    Yes I refer to it as a “Bizarre Marriage Related Accident”, I have done rescue calls where it was hand into tree chipper, hand vs metal punch, hand vs meat slicer… it was just my time. Regarding the “give the finger” jokes, we did a finger amputation call (rescue squad) at 2:00 AM where they found the finger after we (the ambulance) left for the hospital as you cant wait around too long on scene looking for body parts. That night the radio airwaves were full of”we have given the finger to MLPD but they gave us the finger back…”

    I think James can scan the cast, that was probably the reason I sent it now that I think about it. I have a very articulate “stub” left that I can palm curl with for actuation. It looks like a finger but it isn’t, they pulled skin from my palm over the bone and cut off what couldn’t be covered.The hand specialist was a true artist.

    For those that have asked offline, if my finger had been cut off it would have been re-attachable but you cant put a finger back on that’s been avulsed off, For those with a stronger stomach you can see a pic of me holding the finger that’s been torn off and still has the distal phalanges in it next to the expose phalanges of the stripped part. http://c128.com/images/avulsed.jpg

      1. When I was in the first ER the doc walked in and I gave him the run-down when I got to “complete avulsion” he looked at me and asked “who ARE you?” since I also had a faded shirt with a caduceus on it. I had probably delivered patients to him many years ago. From that point on he introduced me by my military and civilian accreditations and let me do “the bullet” report, which helped with a relaxed atmosphere since I could take part in my own treatment.

        1. Most doctors aim for and dread patients like this.

          That is,
          1) Doctors desire patients to actually achieve an understanding of whats going on, and how sometimes there is not “good” option, only the option the doctor/surgeon thinks is the best chance for the best achievable outcome, so that they can partake in the definition of what is actually a “good” outcome. And accept the possibility of a not-so-good outcome, too.

          2) Many patients who achieve more than usual understanding, achieve it through heresay (i.e. the internet) and, having not gained perspective on that understanding, fall to the inbuilt instinct to presume that you’ll always win if there’s at least 1 in 100 chance – often insisting on the thing that worked for that guy with something that sounded kinda the same, no matter what the person who they expect to deliver that care thinks.

          I wonder, did you find a similar dichotomy of expectation? Did you find that your prior experiences (I’m presuming largely of the start of the process rather than the end) gave you an ability to partake more in the descision processes, understand the uncertainty more, or make it harder for your team (or yourself) to focus on the impact because of the cover of professionalism.

          Just interested.

    1. Howdy. I’m a mechanical designer with a background in SFX animatronics. I’ve been playing with soft robots for the past few years at Super-Releaser and I’d love to help develop prostheses. Please keep me in the loop.

    2. Bil, If you’d like to email you have my permission. Also would like to say that Steve Wozniack, Jeri Ellsworth, the HAD staff and anyone else I admire is also welcome to email me.
      Bil, does the strength in the first joint of your short finger equal the strength in the other fingers?

  10. You did a great job with the whole process. I used to teach advanced make-up techniques, and everyone had to make a plaster cast of their face so that they could then build custom latex prosthetic pieces for their final project, and I know it’s hard to keep your eye on the details throughout the whole long slog.

    I only ever had one minor incident. When you make a mold of someone’s face, you have to put straws up their nose so they can breathe, and of course some people panic when they have their entire face covered with smothering goo. I taught everyone hand signals for yes and no so they could answer questions about how they were doing, and I also gave them a panic gesture that meant “Rip this stuff off my face RIGHT NOW!”

    So one student was putting the final touches on the layer of molding compound on this female student’s face, and he accidentally brushed one of her nose straws pretty hard. She let out a muffled yelp of pain, but then quickly signaled that she was okay to keep going. About 10 seconds later, blood started to drip very slowly out of her straw. The entire class looked at me – should we tell her? Knowing that she would probably have to sit through the whole process again in order to make her face cast and get a high grade on her final, I decided it was better that she not know. We put a towel under the end of her straw and kept going.

  11. I lost the tips of my index and middle fingers on my left hand while using an ancient shaper (I’m left-handed). I played around with designing my own prosthetic and finally went to Hangar to have some made. I ended up with some really nice looking prosthetics, but they are not very useful. Without tactile sensation they are just silicone lumps on the ends of my stumps. I have adapted to just use my stumps as best I can. My prosthetics do look incredibly real, however, so they are great for pranks. I’ve smeared them with strawberry jelly and left them on the table saw for ‘the new guy’ to find. I’ve dropped them in a Guiness and then told the bartender that there was something in my beer while I fished out the fingers. My favorite prank was in a sushi restaurant where I laid the ‘fingers’ on the platter among the sushi and asked the FOB Korean waitress what kind of sushi it was. She screamed and burst into tears. I felt bad and left a big tip. Good times.

  12. I have the same lost finger on my left hand because of an explosion when i was a child, I’m really curious and i look forward to see what will be able to have soon.
    Please keep us informed !

  13. Bil,

    Tough luck but you are a tough guy. At least it didn’t take your attitude. My initial observation is that the main purpose of the flexors is to curl the finger downward so as to make contact with the thumb, resulting in a grasp. Having a now shorter length to the finger means that thumb contact can be made without any flex to the finger and only requiring some palm curl. The question I have is whether the flexors and extensor were attached to the remainder of the finger. If so, it would seem that you might have good motion with it. The downside to a prosthetic would be a loss of tactile feedback. What degree of feeling does the finger currently have?

    Yes, I would be happy to assist in any way. I do have more questions than answers at this point but am intrigued with your challenge. Sign me up

  14. Don’t know if I can contribute but will follow with keen interest. Having crushed both sets of fingers in different accidents and working with people with disabilities in the past I understand the frustration people feel when functioning is impaired.

  15. Thanks again everyone and sorry to hear about similar injuries. To answer a few questions; yes I have strength abduction and adduction and yes one of the goals would be to create an opposable point against the thumb. I can’t pick up a handfull of ice cubes or change without things leaking out on the floor, (which still doesn’t explain why my socks are hanging on the doorknbob and light fixture.) I also have side-to-side motion and if the prosthesis tip could relay simple sense like pressure to the remaining part (I named it “stumpy”) that would be interesting. Heh… imagine a small peltier device that could relate hot and cold. (I suspect one of the more modern heat pipes could do it mechanically)

    1. See, now this is a good idea: load up the replacement finger with sensors (strong magnet for locating A/C, RFID / NFC communication, thermometer, etc etc) and make it even more useful than the original! Take inspiration from this: http://hackaday.io/project/2736-Bionic-Yourself
      or any of the other various (useful) body-mod projects.

      I wonder if the base could be fitted with six individually movable pins (poke in/out) such that it could speak Braille to the tip of your shortened finger, and read out temperature, compass direction, etc.

  16. This is why I wear my wedding ring on a ball chain around my neck. Saw too many pics of this when I was in the military. It’s been there for the last 20 years. It’s only come off a few times in that period. My grandpa lost his to a truck door. Crushed the ring down so tight only some skin and tendons were holding the parts together.

  17. Just signing on to see what develops. Yup I lost a digit too. I’m pretty keen on a radar guided laser-cannon option. A concealed cigarette lighter woulda been cool a few decades ago. I too can do gang signs that nobody else can. AND I can count in fractions on my fingers. Great video.

  18. You mention plaster of Paris molds at the beginning as he old way of doing this, before alginate.

    DON’T use plaster of Paris!!!!

    PoP generates a lot of heat as it sets, and I know of at least one person who severely cooked his hands when making a mold.

    1. if you mix plaster of paris with joint compound you cut down on the temperature it reaches, and it gets softer as is easier to fix imperfections. The downside is that it needs to set much longer than normal plaster.

      One more thing, is that plaster will heat up allot if you use too little water. You want the stuff the consistency of yogurt. not paste.

  19. guess theres a good thing about not being intoo jewelery or being married
    one thing you can do after the vows is slide the ring ontoo a gold chain and hang it around youre neck , might be wize to choose a chain that doesnt hang you ……..

  20. i think it might be eazier to print a 3d skelleton finger and cover it in skin coloured silicone
    i would only add the second knuckle to the printed prostectic finger and keep the last knuckle without a hinge in a permanently slightly bent angle wish would look somewat natural anyway
    then just slide it over the stump and use some hansaplast to tape a ring around both the middle/pinky finger and the prostetic finger between the second and non existend thirth knuckle and it whont come of and move with the finger its taped too
    you can allso hide the seam/joint of the prostetic using the weddingband that caused accident in the first place and if they do a good job on the skintone of the add on finger people whont even see its fake

    it should be relativaly simple mecanicly and be sturdy enough to work in daily llfe

    it might be a good idea to allso cast the ringfinger on youre good hand so they can use it to cast it in silcone rubber and use that to cover a 3d printed skelleton for the new finger add a fake nail filed to size and youre done , you even have fingerprints if you use a good enough alganate

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