Tuesday, March 10, 2009

Tech Tip Tuesday

The Football : Part one...

The Football? Ahhh... It's really easy. Look at the bottom of this canoe:

If you were able to look down on the top of the canoe, the opening on the bottom would look like an American football. It's really garboard panels built up from strips.

When my students build canoes, we avoid fitting every single bottom strip in favor of making one mating joint across the center of the canoe's bottom at the keel. There are many, many ways to finish to bottom, but I feel this is the easiest way to do for beginners and gives good results. There are several good reasons - it's easier to make a single straight line and with this method, any issues at the ends of the football are hidden between the inner and outer stems, and it is faster to build.

I usually decide where to start by measuring back about 2" from the end of the inner stems at the keel. If the next strip covers that part of the stem, that's where I'll start. The reason is that the outer stem will come to within about 1" from the end of the inner stem at the keel. This way, the end of the panel is hidden between the inner and outer stem, camoflaging and gaps. On the canoe in the first picture, there were about 3 more strips per side that went on the hull before we started the panel.

You determine where the football starts and leave that strip un-glued, but nail or staple in place as required, and then continue to build one half of the canoe. Mark this first strip with a pencil so you know which one it is. This will be important later.

The remainder of the strips used to build the panel are then glued and stapled into place like the rest of the hull until you've built past the centerline of the canoe. It is imperative to have enough material to cut away at the centerline. Don't skimp - add another strip if you're close:

Before removing this panel, the glue must cure comepletely. You should also mark the panel clearly to know which end is which and how it was positioned along the length of the canoe. I label the bow and add two hash marks that run over the "dry" joint.

While the panel is still in place, I also reach up underneath the panel and make marks with a pencil at every station to indicate the centerline. On this canoe, the centerline was on the other side of the patterns.

Now that the panel has been marked, remove all of the fasteners that held the panel in place while you were building it. Remember the mark you made to indicate the first "dry" strip? This is when it becomes important! You don't want to remove fasteners from the rest of the canoe yet, just the bottom panel.

After the first panel is removed, repeat the steps above, and build another panel on the other side of the canoe.

We will then build the second panel the same way as the first panel marking the panel orientation and position, but not the centerline. When the panel is dry, remove the fasteners to the first dry joint and remove the second panel.

Now, you can connect the centerline marks and cut on your first panel. Using clamps and a batten, position the strip on your centerline marks and make a continuous line in pencil. Be aware - the panel may have flattened out slightly after removal from the hull and the line may not be perfectly straight, but deviates a bit at either end. Don't worry about this much.

The centerline marked on the first panel:

At this point, we'll cut the panel about 1/8" proud of the line using the bandsaw to remove a majority of the waste from the panel. We then dry-fit the panel on the hull and holding a small plane with the sole vertical, we cut small sections of the panel close to the marked centerline at the appropriate bevel angle. This will help act as a visual guide to get the correct angle for the rolling bevel cut on the panel.

Then, with the panel in a vise, we plane the panel's rolling bevel to match the small test patches and down to the centerline. Be sure to plane from the center of the panel towards the ends of the panel to avoid splitting the strips along their grain. This is very important. Also, use the plane with the longest sole possible to get a good, straight line.

Now that you've trimmed the first panel, put it in its' proper location on the boat and put the second panel in place as best you can. Reach underneath and scribe the first panel's edge on the second panel. Use the batten to mark the second panel in the same way as the first. Cut on the bandsaw again, but leave 1/4" minimum for waste. When done, it should look like this:

To be continued next week.

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