If you've ever watched much of Roy Underhill's show The Woodwright's Shop on PBS, you've seen him use a self built treadle lathe. If you haven't watched much of Roy Underhill's show, why not!? Seriously, look up if/when it shows in your area and watch it!
I'm working on a wooden sailboat mast. It is 14 feet long and constructed with the birdsmouth techinique. I wanted to round it, but a lathe capable of handling a 14 foot long workpiece isn't exactly common... or cheap. So, what to do? I started out with an octagon; the shape the birdsmouth build produced. I used a hand plane to knock off the corners to make it 16 sided. Then again to make it 32 sided. That is pretty close to round. How does one make it rounder? Sanding.
One common way of sanding masts is to turn a belt sander belt inside out and use a drill equiped with a disk to turn it. I don't have a belt sander and as such no belt sander belts. I didn't really want to buy one, nor did I want to stand around running a drill for a long time. Especially since my drill isn't really that good of a drill. I came up with my own way.
Step 1: Tools and Materials
Scraps of wood
Something to attach string to and throw
Step 2: The Spring
You need a rope over that branch. I used an old tennis ball with a hole poked through it for my throwing weight. Tie the string to the weight and lay out a bunch of string on the ground (roughly 2x the height of the branch above the ground) and make sure it isn't tangled or snagged on anything. Throw the weight over the branch and work the string up and down to get the weight within reach. It took me many, many tries. I think I hit the branch 7 or 8 times. I managed it over a few times, but couldn't get it to come down so had to pull it back and start over. Other times, I simply threw it under the branch.
Once the weight is over and within reach, cut off the weight, tie a loop in the string, and feed many feet of rope through the loop. Don't tie it, or the knot might get caught. Use the string to pull the rope up and over the branch. I tied the rope into a big loop that hung a foot or so above my head. That way, I can untie it and easily pull it down when I'm done.
Step 3: Work Support
Step 4: The Drive Rope and Treadle
Later I discovered that the direction of wrapping can be important. It was easier to have the end of the drive rope connected to the treadle closest to where I was standing. Positioned with it on the far side, it had a tendency to over-ride. The drive rope can be moved up and down the workpiece to some extent as necessary to work on different areas. The sawhorses can also be moved in relation to the branch to re-position the drive rope.
Step 5: Use
I was sanding, so I held strips of sandpaper against the mast. If one is feeling daring and wants to do a little more shaping, another sawhorse might make a useable tool rest for a lathe chisel. Since it is relatively low speed and low power, the risk of injury is somewhat reduced. Still, don't be stupid. The rope can pinch, a chisel could catch and be thrown, you could lose your balance and fall, the tree branch could break and fall on you, etc.
Sorry, I didn't take a lot of pictures. A video of it in use would have been good too. Maybe next time.