I got an ordinary piece of spruce 2x6 for the mast. (actually picked through the stack for the best of the ordinary, and knots should be small) I snapped a line between marks 2" in from opposite corners. Did you follow that? This makes two tapered pieces 31/2" at one end and 2" at the other. I buttered them with Titebond II and clamped them. This board had a very slight curve in it. However, any tendency to bow can be canceled out by this process. I faced the cup of the bow inward... like this...( ).
Mast: At last report we'd only glued up the mast cut from a spruce 2x6. This gave us a taper to only one side. The other edge is 3" wide the whole length at this point. I measured the tapered edge at several points then transferred this measurement to the non-tapered edge, and centered it. I then connected the marks with a straight edge. This could have been cut with a circular saw, but I planed to the marks.
This is a simple but effective mast marking gauge. It helps you put lines on a tapered square blank to turn it into an octagon. It takes a 14" stick with 4 holes in it. Two nails, and two pencils. The spacing is 7 - 10 - 7 units of any kind. In this case it's 3.5" - 5" - 3.5". The nails that slide against the mast stock should be placed so their inner edge touches the measured mark. Don't drill on the mark. I wont bother to explain the geometry of it. It's ol' Pythagoras again. A squared plus B squared = C squared. But there's no need to understand it to use it.
Here I've removed the stock between the lines to make an octagon. You can set your circular saw to 45 degrees and cut just outside these lines, then finish off with a plane. I used a power plane. (Then shoveled the shavings off the shop floor.)
Then I got real fancy and drilled a hole in each end, tapped a piece of 1/4" brass rod into the holes and mounted those between to scraps of 2x6 clamped to a 12 foot 2x4. Looks like a huge lathe. The friction is such that it squeaks when I turn it, and it will stay put while I use the planer on it. I'll explore sanding gizmos next.
I made a gizmo I call the "rounder." I saw Gregg Rossle use this at the Wooden Boatbuilding School in Brooklin Maine last summer. It's one of those gizmo's that once you see it seems obvious. Great for changing that faceted stick into a rounded spar. You can cut a sanding belt into a long strip and attach wooden handles to the ends and go after it "shoe shine" style, but this gizmo is many times faster.
Here's the gizmo. It's a wooden drum about 3" in diameter and 6" long mounted on a 5/16" threaded rod, with a handle that "idles" meaning the rod can spin freely inside it. My handle is plastice pipe, Gregg uses copper. I made my drum by cutting out a stack of disks with a hole saw. They're sandwiched onto the rod between washers and double nuts (to lock them tight) it's covered with tape to give it a crown shape, then rubber. Gregg uses inner tube rubber, I had some industrial rubber backed carpet around that I stapled on rubber side out, and it seems to work.
After doing a coarse and medium belt I switched to 100 grit on my orbital Porter Cable sander. It's amazingly easy to sand a cylinder with a circular motion. I found my pair of "shop mate" saw horses with the crank clamping set up were a big help. For the "rounder" I clamped the mast firmly, but for the orbital it held fine just resting in the gaps of the saw horses.
I finished sanding the mast and gave it several coats of water based sealer called Hydroclear by Burgess. I used the same finish on the tiller and it looks and feels great. It's a cinch to apply with a cloth, fast drying. We'll see how it holds up. I also have some Hydroguard they tint for UV protection but the color was a bit orange-ish for my taste.
I used the same hole saw that I made my mast step with, to size the base of the mast. After drilling into the center of the base I used tape to guide my saw around the perimeter. A tidy ring of wood popped off and the mast now fits the mast step perfectly!