The Kassel Hand Project

Printable Sixteenth-Century Prosthetics

Experiments

Whether you’ve printed and assembled your own model and are ready to test it out or you want to see what an assembled model looks like in action, check out the videos below. There are suggestions for modifying the Work-Alike for a residual limb, tips and tricks on how to operate all the models, and a couple of experiment ideas.

Operating and Modifying the Models

Tips & Tricks to Operate the Model

Here are some useful troubleshooting tips for using the model:

  • The release lever, which looks like a trigger on the outside of the shell connected to a “paddle” shape on the inside of the shell, only needs to be pulled back slightly to create the action needed in the mechanisms. This component is often the first to wear out and break in the model, so consider printing extras to be prepared to replace it.
  • When releasing the four fingers (index, middle, ring, little) from flexion, dip the model downward and use gravity to assist in resetting their position to full extension. Sometimes a slight downward tilt is enough, but don’t be afraid to dip the model at a more extreme angle if needed.
  • Here’s what to do if one of the four finger sticks:
    • While the model is dipped downward with fingertips toward the floor, give the shell a little shake up and down and side to side.
    • Look inside of the shell to check that the finger pawl of the stuck finger lowers slightly when you activate the release lever. If it does, that means the mechanism is working. If it doesn’t, that means the pawl itself might be stuck.
    • If you’ve confirmed the pawl is moving but the finger is still sticking, carefully use a tool (such as a pick or pencil) to manually lever the pawl up by sticking the end of the tool between the proximal end of the affected pawl and the “paddle” of the main release lever.
    • If the finger keeps sticking, it might be a sign that the distal end of the pawl needs a little more filing.
  • If the thumb sticks, try the “rocking” technique to operate it:
    • Activate and hold the release lever, then gently press the thumb forward (in the direction of flexion) before pulling it backward to extend it
    • Be careful not to apply too much force to extend the thumb–if you force it, that can cause the thumb pawl mount to simply delaminate from the interior surface of the shell. Rock the thumb forward then back rather than try to muscle it back.
    • If the rocking technique isn’t working, look inside the shell to ensure the release lever is activating the thumb lever or open the entire shell to examine the components.

Considerations for Modifying Work-Alike to Wear on a Residual Limb

Here are some suggestions for modifying Work-Alike to your specifications:

  • Modify the wrist casing to your measurements. The dimensions of where the shell opens should take into account your residual limb plus a protective sleeve or anything you plan to use as a barrier between you and the plastic model.
  • Protect your residual limb and the mechanisms with a socket interface of some kind. In our study, we integrated a 3D-modeled socket into our CAD of the top half of the shell so that the top half of the shell and the socket printed in one piece. In hindsight, we would probably have a socket separate from the top shell and connected by a hardware attachment. Think about how you might want a socket to interface with the shell.
  • Consider attachment options using the holes in the proximal end of the wrist casing. Substituting purchased metal hardware in place of Lookalike’s plastic ring clip and ring or using a combination of a thickened plastic ring clip with a metal ring are a couple of ways to approach the wrist casing itself.

Experiment Ideas

We developed a few historically grounded activities to test the model during our two-year project. Our experiments focused on picking up various drinking vessels, picking up a candlestick, lifting and moving a small box, untying and tying a short lace, grabbing and pulling the reins of a horse, and simulating opening a chest lid. All of these activities drew representational dimensions and weights from historical artifacts to consider how the unknown historical wearer of the Kassel Hand may have used the prosthesis. (For a detailed explanation of our method for experimenting, keep an eye out for a forthcoming article in The Bulletin of the History of Medicine!)

Below are two suggestions for historically-grounded activities drawn from our experiments that you can try out yourself to think about how the Kassel Hand may or may not have been used and why.

Römer Cup

A Römer was a type of glass drinking vessel that appeared in Germany and the Netherlands in the sixteenth and seventeenth centuries. Its tell-tale shape featured a hemisphere bowl superimposed on a hollow cylinder dotted with pads of glass called “prunts.” Our 3D-printed Römer took representative dimensions from an artifact (LP 2010-113) at the Glasmuseum Hentrich of Kunstpalast Düsseldorf (special thanks to Dr. Dedo von Kerssenbrock-Krosigk for his generous assistance).

Print Your Own Römer cup

If you decide to test picking up the Römer yourself, we encourage you to think about whether or not using the model seems practical for the task and what some advantages and disadvantages of using the model to perform this task might be. Tip: we added 9 oz of stick-on weights to the hollow cylinder of our Römer to represent the weight of the artifact plus the volume of liquid it could hold.

The Box

A casket was a sixteenth-century object with a basic geometric shape that could have been used to hold many different kinds of smaller items of value, from documents to jewelry. Objects like this could be found in domestic and institutional settings. Our test box has representative dimensions drawing from multiple artifact examples, including the weight and handle shape of a casket (K 3069) at the Kunstgewerbemuseum, Staatliche Museen zu Berlin (special thanks to Dr. Jan Friedrich Richter for his generous assistance).

Our test box was purchased from a craft store. We added a three-pound dumbbell inside to give it some heft and 3D-printed a handle that we attached with hardware. Check out the dimensions below if you’d like to simulate your own version.

Object Dimensions

  • Box
    • Length: 29.5cm
    • Width: 19.5cm
    • Height: 13cm
  • Handle
    • Outer Length: 7.9cm
    • Inner Space: 6.8cm
    • Height: 2.8cm