Knick's Prosthetic Finger v3.5.5

thingiverse

Here is a step-by-step guide on how to assemble a robotic finger: **Materials needed:** * PLA or ABS parts * Elastic cord (preferably NinjaFlex or FilaFlex) * Fishing line "tendon" * Hinge plugs * Set screws * Bumper material (e.g. Sainsmart elastic TPU) **Tools needed:** * Drill press * Files * Jigsaw or coping saw * Exacto knife * Soldering iron * Coffee warmer (for warming up hinge plugs) **Step 1-12 Assembly:** 1. \nPre-assemble the finger segments by cutting them to size and sanding down any rough edges. 2. Assemble the hinge pins and ensure they fit smoothly into place. 3. Pre-assemble the hinges. (1:27) \nPre-assemble the 3 PLA parts and ensure that they all work smoothly together. Push the pins (or wire) through the hinge holes, ensure it's long enough to make it all the way through both sides of the hinge. \nIt should take nearly zero friction to move the segments across their full travel - if you can't fully articulate the finger using only gravity, then keep working at it with the files until you can - or else it won't work well later. 4. Install the set-screws (1:45) \nEach of the two lengths of elastic has a knot on one end, and a set screw on the other. \nYou'll need to get the set-screw holes just to the right size. Too small and the screw will be hard to turn, and can crack the plastic. Too big and it will slip out - a 1.75mm bit works about right for me. You might want to practice on a scrap piece. 5. String the elastic (2:14) \nFor the tip, run it through whichever way is easiest. I sometimes use a small drill bit or length of wire to help me push it through. Tie a tight triple square knot on the end that protrudes from the bottom of the middle segment. Trim it neatly, and it should pull flush. For now leave a couple inches on the other side. \nFor the base, I use a double knot on the side coming out of the end of the middle segment, in the gap of the tip hinge. It will sink down flush. If it pulls through easily, try again with a triple knot. Then on the base the elastic will protrude in the socket area with a set screw. 6. Tighten set-screw to create tension (4:15)\nPut slight tension on the elastic cord and carefully tighten the set screws to hold in place. You'll want the base knuckle just barely tight enough to pull itself fully closed. The tip should have slightly more tension, to compensate for the additional leverage that it has. trim all but a small amount on both sides, for later adjustment.\nIf you're not using set-screws, you'll need to tie knots on both sides of the elastic. I find it easiest to stretch to the desired tension and then mark the elastic with a bright paint marker. This way as you're tying the knot you can get it just at the right spot. 7. Install the hinge Plugs. (4:25) \nI warm the hinge plugs on my coffee warmer for a while, making them soft and easier to squeeze into the ends to hold the pins in place. You should now have fully assembled hinges. 8. String the fishing line "tendon" (5:23) \nString the fishing line through the tip, down under the middle section, and back up through the base. Tighten the set-screw at the tip, leaving just a small amount for later adjustment. Leave 3 or 4 inches on the base side, to ensure you have enough to connect it to your wrist linkage. 9. Test the action! (6:04) \nAt this point, you can snap the socket and tip on, and should have a fully articulating finger! Make sure it all works well before moving any further. 10. Install the bumper. (6:09) \nIf you use NinjaFlex or FilaFlex (more stretchy) you can probably stretch the bumper enough to get it over the tip and on to the middle section - that stuff is almost indestructible. \nLately I've preferred the cheaper Sainsmart elastic TPU, but it is not as stretchy. I print it with the cut in the bumper, which you can separate carefully with an exacto. Then wrap the bumper around, and trim the plugs as needed until it fits together well. Then I use my soldering iron (set around 3/medium) to heat up the edges of the bumper. 11. Assemble the wrist joint by attaching the fishing line "tendon" to the base of the finger and securing it with a set screw. 12. Test the entire assembly to ensure that all parts are moving smoothly and that there are no loose connections. **Tips and Variations:** * Use a drill press to create precise holes for the hinge pins. * Experiment with different types of elastic cord or bumper material to achieve the desired level of flexibility and durability. * Consider adding sensors or actuators to enhance the functionality of the robotic finger.