Introduction: Wooden Hobbed Gear Do-Nothing Machine
My original present for my brother fell through. So a few days before Christmas, I called him and asked him what he wanted. He told me he wanted something for his office, and I decided to make him a desktop toy. I looked around and was inspired by a do-nothing machine that this guy made. I had recently used a tap and die to make a nutcracker similar to this one and figured I could use the tap to hob a gear, and the die to cut a grub screw.
Step 1: Plans
First, I sketched it all out. I based the machine off of f the scraps that I had around. I used black walnut for the gears, oak dowels for the gear post and screw axle, and some random wood a neighbor gave me for the structure.
Step 2: Making the Gear Hobbing Post.
There's probably a real term for this device, but I'm going to call it a hobbing post. Later you will use it to hold the gear on the tool rest while you cut the teeth. To make it, you just need to turn a 5/8 inch dowel from a dense hardwood, and then turn a 1/2 inch tenon into one end of the dowel. The resulting piece should fit directly into your tool rest.
Step 3: Make the Main Gear
Next it's time to make the gear. This part turned out to be much easier than I expected. After you turn the disc, drill a 1/2 inch hole in the center. Replace your tool rest with the hobbing post and put your gear blank on it. Now, put your 1 inch tap into the lathe chuck and push your gear so that it is snug against the tap. When the lathe spins, the tap will turn the gear and cut teeth into it as it goes. Turn the spindle of the lathe by hand for a couple of gear rotations to get the teeth started. Once you have some decent grooves, you should be able to run the lathe at low rpm's.
I got best results by making sure that I was toward the top of the tap, where the threads are the deepest. If you pull the gear near the bottom of the tap, the shallow thread depth will grind off your gear teeth, resulting in an ugly, less functional gear. Also, I found that there was no need to lock down the tool rest. With the lathe running on low RPM's you should be able to gently push the gear against the tap and let the machine do the work. Initially, the tap will cut the teeth unevenly, resulting in some split or crushed teeth, but eventually, it should carve the blank down to a diameter with even, well-defined teeth.
Here is a short video of what it looks like.
Step 4: Rough Out the Worm Gear
Turn a 1" dowel. This will eventually be the worm gear that drives your do-nothing machine.
Step 5: Cut Threads Into Your Screw.
Once you've turned the dowel, cut threads into it with a 1" thread cutting die. After you've cut the threads, mount the screw on to the lathe again and cut 3 or so threads off of each end.
Step 6: Drill Axle Holes Into Your Screw.
Ideally, you should do this before cutting the threads, but it's not the end of the world if you don't. Cut 3/8 inch holes about half an inch into both ends of the grub screw. When you assemble the machine, you will glue dowels into these holes to serve as axles.
Step 7: Cut the Pieces for the Structure.
For my machine, I cut three pieces that were 3 7/16 inches by 5 inches to serve as the sides and bottom of the machine as well as one 3 inch by 3 7/16 inch piece for the back.
Once you've cut the pieces, tape the side pieces together and cut the desired profile on a bandsaw. Keep the sides taped together and drill a hole through both of them about 2 1/2 inches from the bottom.
Now you should have sides that are perfectly symmetrical and have a hole straight through.
Step 8: Determine Gear Post Positioning.
Cut some 3/8 inch dowel sections for your worm gear axles. and do a dry assembly of what you have so far. Hold the main gear against the worm gear, and measure the height at which your gear will rest.
I really wanted to avoid having any metal hardware on this piece, so I opted to have a dowel go through the bottom of the structure. I determined the location of the hole by placing a pencil through the center of the main gear and using the mark as my distance. This was not very accurate, and I ended up having to resize my gear. I would suggest either gluing or screwing in the main gear post as the last assembly step as a simpler, more forgiving method of mounting this piece.
Step 9: Make Your Gear Post.
Cut the 1" dowel to the height you determined. Mine was 1 1/2 inches. After it is cut to length, mount it to your lathe and cut a 1/2 inch hole on one side and a 3/8 inch hole on the other. Glue the appropriate sized dowels into the holes. This is the post that your main gear will sit on. The 3/8 inch hole will go through the bottom of the structure.
Step 10: Final Pieces.
I forgot to take a picture of this, but you need to turn a knob and a retaining cap for the main screw from a section of 1" dowel.
Step 11: Put It All Together.
Before assembly, you should put some kind of finish on the gears. I chose danish oil, in hopes that as it hardened, it would help strengthen the gear teeth.
Next, glue your structure together. Put a spare section of dowel through the holes in your side pieces while they are being glued to ensure that they will remain aligned.
Glue your gear post into place. Once the glue is cured, flush cut the dowel on the bottom and, sand and finish the whole structure.
After the finish is dried glue on the end of 2 sections of 3/8 inch dowel and glue your worm gear into place. Glue the knob to one of the protruding dowel sections, and cut the other section flush to the side of the structure.
Once all of the glue is dried, put some finish on any pieces that still need it, and you're done.
Step 12: Do Nothing!
Now that your machine is finished. You're ready to do a whole lot of nothing. Do nothing to the right, and when you're tired of that, do nothing to the left.