In the event that you wake up one day and think, "Gosh, I could really use a fifteen-foot mast," I'm going to teach you exactly how to make one yourself, starting from scratch.

Actually, this tutorial is informative not only for aspiring boatbuilders, but for any application where you need to turn square stock into round stock.

The materials are easy to acquire, but you will need access to basic woodworking machinery.

Supplies

Hardwood stock - Sitka Spruce or Douglas Fir are traditional materials
Wood glue - Titebond III is waterproof, affordable, and readily available
Two Bic pens
Two copper roofing nails

Tools

Table saw
Jointer
Thickness planer
Lots of clamps
Drawknife or power planer
Hand plane (#3 or #4 Stanley)
Sandpaper
Pencil

Step 1: Buy Lumber

Hit Up Home Depot

Assuming a fifteen foot mast, your finished dimensions will be 15' x 2.5" x 2.5". Depending on your geographic location, you should be able to find Sitka Spruce or Douglas Fir at your local box store or lumber yard.

If the lumber does not come in 15' lengths, buy enough lumber to splice two shorter sections together. If your lumber is less than 2.5" thick (likely) you will need to glue up two pieces for thickness.

Take the time to pick through the pile, looking for stock with tight grain.

Step 2: Mill and Dimension

Milling

Back at the shop, mill your stock square and parallel. If needed, glue up stock to get 2.5" thickness. Clamp and leave 24 hours.

Gluing

Be sure to use waterproof glue. Titebond III is appropriate for outdoor applications, and readily available at hardware stores.

When clamping, remember that clamping pressure radiates at 45deg from the clamp heads. Use enough clamps to apply consistent pressure over the length of your stock.

If splicing, cut a 1:12 slope at the ends of your stock and glue up to get the required length.

Step 3: Square and Taper

Clean Up

Using a hand plane or cabinet scraper, remove any excess glue. Joint and square one set of adjacent faces, then square the stock with a thickness planer. Cut to length. Your stock should now be 2.5" x 2.5" x 15.'

Tapering

If you are making a mast, you will want to taper the pole. Rather than apply a consistent taper, boatmakers like to use a gentle arc. Think of a blade of grass bending in a breeze. This provides strength when the sail is tugging on the mast.

Draw a center line in pencil on your stock. Your mast will taper from 2.5" at the bottom (0') to to 2" at a point near the top (13') and finally reaching 1.5" at the very top (15'). Mark these dimensions.

The profile of your taper will be drawn with the help of a batten - a flexible piece of wood which ensures a "fair" curve free of bumps. Any thin cutoff will do, so long as it is sufficiently flexible and of consistent thickness. Use clamps or lead weights to hold the batten in place, making sure it touches the three marks you just made. Trace the line.

Repeat on the other side.

With a drawknife or power planer, take the thickness down to your line, on both sides.

Repeat the process of marking the remaining two sides with the batten and shaping them with the drawknife or power planer.

Clean up the faces with a hand plane. You should now have a tapered rectangular pole.

Step 4: Octagonize

Making a Spar Gauge

This is my favorite step, a feat of ratios. It also involves a made-up word: octagonize.

The first step to rounding a four-sided spar is to make it an octagon. Once you have eight sides, it's easy to move to sixteen sides, and finally to the round.

Making your own spar gauge is surprisingly simple. Any scrap of hardwood will work, so long as the edges are square. Break two Bic pens and retrieve the inkwell reservoir. You can discard the rest of the pen. Insert two copper nails as fences at a distance slightly wider than your spar, and insert the inkwells between them spaced at a ratio of 1 : 1.4 : 1. You'll want to tap holes with a drill press or power drill first, and use the correct bit to ensure that your inkwells fit snugly.

A spar gauge will allow you to draw the edges of an octagon on any square stock as you drag it along, even as it tapers, thanks to the magic of ratios.

Use the spar gauge to mark a set of opposite faces, then work down to your line with a draw knife or power planer. Clean up the surface with a hand plane. Repeat for the remaining two faces.

Step 5: Sixteen to Round

From Eight to Sixteen

Every foot or so, draw a straight pencil line around the circumference of the mast. Using a hand plane, take passes along the length of the mast until the remaining line and the flats in between are of equal length.

From Sixteen to Round

At this point, you can almost taste sweet victory. Using a hand plane, take the corners off the sixteen sides. You will be close enough to round to sand your way to the finish line.

Sweep up your shavings. Find the nearest taco truck and reward yourself.

Step 6: Finishing

Finishing

Two options for finishing spars for marine use are:

Marine varnish, such as Le Tonkinois, which dries amber and glossy and needs retouching every season
"Boat soup," a combination of boiled linseed oil, turpentine, and pine tar, a much lower maintenance "workboat" style finish

Be sure to use gloves and apply in a well-ventilated area.