Tuesday, April 28, 2009
Tech Tip Tuesday
One of the more misunderstood stages of building a nicely shaped canoe is the fairing process. No matter which method that you use to strip your canoe, because you are building a curved shape with a collection of flat strips, you will need to fair the hull. By fairing, what I mean is to create a smooth, continuous shape around the canoe from gunnel to gunnel and from end to end. This is a very important process. When you apply fiberglass to the hull, any dips, bumps or unfair curves will stick out like a sore thumb.
The tools of the trade are in the picture above. They should be sharp. Hair shaving sharp. As one of my students used to say, "scary sharp". The soft cedar can tear easily if the tools aren't sharp. What we have are some low angle block planes, spokeshaves (flat and curved sole) and some home-made longboards. For most of the canoe, the block plane is the best tool for the job. If you have some "hollow" areas, the spokeshaves are the best choice because of their small footprint of the tool. The longboards come into use after the edge tools are done.
I have to issue a caution here. The temptation of the beginner is to take a random orbital sander and have at it. The problem here is that the random orbital sander is typically a 5" or 6" diameter disc. This is a fairly small area and most people wind up using the edge of the tool to try to fair the hull. The usual result is a rippled hull. As you look down the hull, you can see the ripple and the fiberglass and epoxy will magnify this effect.
I should also comment on conditions for the fairing process. There should be lots of light. Particularly light at a grazing angle to the hull so that it shows any lumps and bumps. If you can manage to do this outside in the sunlight, so much the better.
This stage happens after the outer stems have been bonded to the canoe and all of the nails and staples have been removed from the canoe. Take a bit of extra time to make sure that you've removed all of the staples and nails as hitting one with a cutting tool is a rude awakening and not too good for your nicely sharpened plane and spokeshave.
The first part of the process is to blend the stems into the hull shape. Basically, you are continuing the curves of the canoe that already exist. Keeping the heel of the block plane on the hull of the canoe as you run the cuting edge of the plane over the stem material is the easiest way to blend the stem into the hull shape. Once this is done, you will start to use a block plane at an angle to the strips. What you're trying to do is to work away the "corners" of the strips and the saw marks in the strips. Keep in mind that your strips are not that thick. Do not stand in one place. It is much faster to use the cutting tools to remove shavings than it is to sand it off, so use the plane and spokeshave as much as possible remove material. If you get tearing of the wood fibers, either work in another direction or re-sharpen your tools. Once the major tool marks have been removed and the hull is fairly smooth, you will move on to the longboards.
Longboards are simply that - long sanding boards without sharp corners. It's hard work. No doubt. You will sand along the lenght of the boat and up over the curves of the hull - a shallow diagonal angle. The sandpaper used is often a 40 or 60 grit belt from a belt sander. All you should have to do with the longboard is to remove any tool marks from the plane and spokeshave.
Once the longboarding is done, a quick, lighthanded sanding with 80 or 120 grit paper on a random orbital sander to take out the visible scratches from the longboard and you will be done. Resist the temptation to use the edge of the sanding disc to "clean up" any problems you may notice at this stage - revert to the longboard or plane as necessary. To ensure that you are done, take a damp cloth and make sure that there aren't any visible glue spots on the hull as they show up like a sore thumb when you apply epoxy and fiberglass.