Storyeater Grabby Arm

Building one requires one print of each STL file, along with some fishing monofilament or similar (I used 30 lb line), a rubber band, 2 M3 grub screws (I used uxcell M3x4mm grub screws from amazon), and some superglue. 

It helps the assembly to also print an extra top piece with just the hand end to hold the fingers in place when adjusting the line tension.

I have printed these mostly in PLA on my Bambu X1C, using a 0.4mm nozzle and 0.12mm layer height. I have also printed it at courser settings in ABS on my TAZ 4, but the small internal holes needed some cleanup or cutting out. It's up to you if you want to leave the finish as is or sand/paint/epoxy them.

I start assembly by cutting 2 pieces of the fishing line about 12 inches long each. Tie a knot near the end of each line then thread it through the small hole in the side of the finger so the line comes out the inside. For extra security, I used the trigger or a clip or whatever to hold some tension on the line, then put some superglue on the knot and let the line hang from the finger to glue it in place. Cut excess line off the knot.

Put a grub screw in each large hole on the trigger. The holes go all the way through but only need a screw on one side. You should use a spare bit of line to test tightening the grub screw until just before it makes it hard to insert the line.

Pick a rubber band that gives good opening tension when looped around the small hooks on the fingers and placed in the main body. You may need to use a longer one and fold it 2 or 3 times.

When the fingers are ready, thread the line through the main body. Each half has some holes and overhangs to keep it in place.

With the lines in, place the fingers with rubber band onto the posts on the main body. Use something to hold them in place, ideally a print of the top half with just the hand end.

Thread the lines through the small holes in the trigger, then place the trigger in the slot in the handle. You should make sure the lines sit inside the body going around the curves between the handle and arm.

Pull one of the lines until the corresponding finger just begins to move. I would then use one hand to pin the line down on the back edge of the handle, then the other hand to turn the grub screw until it's tight. Pull the trigger a few times to test that the line doesn't slip.

Repeat for the other finger line.

You might need to loosen a screw, re-tension, then re-tighten to get the fingers to come together as you would like. There is some play in the trigger so test pulling it at different points and watch how the fingers come together until you're happy with it.

Once you're sure you're happy with the line tension and the grub screws are holding the lines tightly, carefully remove whatever is holding the fingers in place and keep them there with one hand. Use the other to apply a little superglue at various points along the topmost surface of the main body. I put some at the locations marked in the photo. Set the superglue down and use your free hand to get the top cover in place. It may take some pushing to get the fingers to settle in place on both sides. Be sure everything moves freely then set a book or something on top of the whole assembly while the glue cures.

Once the glue is done it should all be good to go. You might need to wipe some residue off from the curing process but that's about it.