I made this chuck to hold small objects between about 1-4cm diameter, on the rotary axis hack I made for my lasercutter. That's why I wanted to design a chuck that could be lasercut. Longworth style chucks are best suited to being cut out of sheet material. I designed the jaws to hold hollow cyclindrical objects from the inside, but you could modify them into dovetail jaws like a normal longworth chuck.
This video also shows my lasrecutter rotary axis build, but I decided to split it into 2 instructables. Please just skip to the timecodes next to each step to see what I'm talking about. The rotary axis instructable is here: https://www.instructables.com/id/Rotary-Lasercutte...
You will need:
- 3mm acrylic sheet
- M3 x 5 or 6mm machine screws x4
- M3 x 15mm machine screws x4 (I used 25mm long ones in the video, but that's not necessary)
- M3 x 10mm machine screw x1
- M3 washers x6
- Solvent cement (waterlike consistency)
6:42 Open the SketchUp file attached to this instructable. Export the two chuck plates, the two parts of the jaws, and all the smaller circular pieces to gcode. I recommend my own SketchUp to Gcode plugin for this: https://www.instructables.com/id/Export-Laser-Cutt...
8:09 Lasercut the 2 halves of the chuck out of 3mm acrylic. Insert the M3 x 10mm screw through one half, thread a washer onto the bolt, then push the bolt through the other half. The washer will prevent the two halves touching, so will reduce friction.
8:28 Lasercut 4 jaws. Remove the protective film from the acrylic and glue the 2 parts of each jaw together with solvent cement. If you want to make different jaw types for your chuck, you can change the shape of the upright part of the jaw in SketchUp.
Not shown in the video - lasercut 4 of the 9mm circles in the SketchUp file - those are 'nuts' to hold the jaws onto the chuck. Lasercut one copy of the 11mm circle. That is kind of a 'nut' that holds the whole chuck together, and can be glued to whatever you want to mount it on. If you want to mount it on a stepper motor, lasercut 2 copies of the 16mm circle with the 6.35mm hole, and 1 copy of the 16mm circle with the 3mm hole. Those will fit the shaft of a stepper motor.
8:42 Screw an M3 x 6mm machine screw into each jaw. The hole you screw it into should be the one furthest away from the sticking-up part of the jaw, that is, the one that will be furthest from the centre of the chuck when it's assembled. Sorry, this is hard to explain in words, but if you look at an image of the assembled chuck, it should be clearer. It's easier to screw into these holes in the acrylic with an electric screwdriver or drill-driver because when the screw turns fast it melts the acrylic a bit and makes its own thread.
8:50 Screw an M3 x 15mm machine screw into the other hole on each jaw.
8:58 Fit the jaws onto the chuck. For each jaw, push the longer M3 screw through a slot in one half of the chuck, thread on a washer, then push it through a slot on the other half.
9:33 Screw a 9mm acrylic 'nut' onto each of the longer screws. Don't tighten them all the way until you have installed all the jaws.
9:49 Fit the shorter M3 screw on each jaw into the slot on the chuck behind the longer one. This will act as a guide to keep the jaws facing the same direction as the chuck halves rotate. Tighten up all the acrylic 'nuts', holding the shorter screws in their tracks.
If you don't want to mount the chuck on a stepper motor, just screw the 11mm circle with the 3mm hole onto the M3 screw through the middle of the chuck, and ignore the rest of this instructable.
10:52 For the stepper motor mount: push fit two 16mm circles with 6.35mm hole onto the stepper motor shaft, and glue them together with solvent cement. If you have a motor with a different diameter shaft, you can change the measurements in SketchUp before you cut the parts.
11:02 Glue the 16mm circle with the 3mm hole onto the other two circles, taking care to centre it perfectly.
11:04 Screw an M3 bolt into the 11mm circle, and screw that onto the 16mm circle with the 3mm hole. This bolt is just a guide to make sure it's lined up correctly. Glue the 11mm circle to the 16mm one, and remove the bolt.
11:19 Finally, place a washer on the M3 x 10mm screw that should be through the centre of the chuck, then screw it into the 11mm circle.