3D Printed Mechanical Hand

Hi my name is Kaamya and I go to Los Altos High School. These are instructions to create a moving hand. I am somewhat interested in creating prosthetics and such, so this was a fun thing to make using Fusion360 skills. I do not personally own a 3D printer [used the schools and a friends] so the version in my pictures has been modified, the instructions for modeling it are a finalized version.

This had a lot of testing and modifying to work, a lot of guess and check. I wanted to make something that interested me, could be easy for others to make, and would move.

You will need:

• Fusion360
• 3D printer w/ PLA filament
• Hot glue and a hot glue gun
• string (here's the one I used, it's elastic-y but still can tense which is perfect)
• sandpaper
• pliers

Now originally I wanted to make this with ball joints because I was drawing them on my hands with pen during class. Having the parts fit together and move using ball joints became a bit tricky to have to model, so I changed my joinery. This is my original design, with your hand using a grip to cause the mechanical hand to close. It's kind of like a puppet in a sense. I like to draw and hands are a struggle to draw, so I have been learning a lot about how they work, and I used that in this. Your index finger really is the only one that moves independently, your others move together.

Try this, put your middle finger down, do others go down too? Do that with your ring and pinky. Do your other fingers try to close?

The strings make it like a puppet in this design since puppets use strings to make different parts move independently. But what if you want your hand to close? Then you need all fingers and your thumb to move together, and that's what I tried to do.

Make sure you set units to inches!

The individual part files are fd3 files, but the full thing is an stl. All parts are on the stl file are on one plane ready to print.

Here is a video of me modeling the bottom finger joint. (without the joining hole because I forgot to include it in the video) If you want to model the pieces on your own you can use the image as a reference and the video as a guide, almost all of the parts are just duplicates so you can use the move/copy tool to duplicate them.

This project has a LOT of supports. And I mean a lot. You are definitely going to need pliers or some sort of tool. I used small scissors since I didn't have pliers, which worked. Be insanely careful because parts are thin and will break easily.

Once all supports have been taken off, sand the joinery down as well as the screw parts with sandpaper.

First assemble the fingers. 4 fingers, each finger has 7 parts.

1 finger consists of:

• Finger bottom joint
• Finger middle joint
• Top joint
• Small screw (x2)
• Small screw cap (x2) [This is so the screw doesn't fall off, hot glue it onto the other end of the screw to secure the joints together]

Repeat that 4 times, and sand down any intersecting parts so it moves smoothly. Make sure it can rotate down 90 degrees.

Then create a slip knot using the string and make sure it's tightened. Put the tip off the finger (top joint) through the loop. Make sure the knot on the loop and the extra string is facing the way you want the finger to bend.

Hot glue it in place to secure.

The thumb assembles like the fingers but it also is a bit different.

The thumb is uses the following parts:

• Top joint
• thumb screw
• thumb bottom joint
• small screw
• small screw cap

Assemble the top joint and thumb bottom joint together using the small screw. Attach the cap so it stays together.

You can angle the thumb if you want to. You have to work quickly on this part. Put the thumb screw through the hole at the bottom of the thumb bottom joint (the part that protrudes and has a larger hole) Put hot glue on the end of the thumb screw (side with no cap). Attach that part to the palm piece where it extrudes on the side. There should be a little groove for the bottom joint to move.

Attach a string using a slip knot to the top joint as well.

As you can see in the photo, I had to make some improvements to it. All the changes I made have been updated in the files linked in this so you should not have to make any modifications.

Line the fingers up with the grooves and put the large screw through all the fingers. Secure it at the end with the large screw cap and hot glue. Make sure the fingers still move and all the strings are facing the right way.

Now you're going to use one backing piece (you should have 2) and secure it with hot glue to the back of the hand so the fingers don't rotate 180 degrees, unless you want them to rotate 180 degrees.

Secure the ends of the strings to the end of the other backing piece with hot glue.

There's a video of my prototype version in this step, it does not work perfectly, but it's a good reference for how it should somewhat work.

This can be improved and I encourage people who make this to do so, it was a fun project and I learned how to use components.