A Shipwright in Training

There was an excellent April fools NPR episode some time back about maple trees exploding in Vermont because the maple syrup farmers hadn’t tapped the trees enough and they exploded from the sap buildup. When we say a board blows up, it’s a little more subtle but damn frustrating. For instance, our breast hook exploded the other day.

Ignore the holes, those were something else. Note, instead, the massive cracks (called checks) at the end of our board. This happens when your wood dries too fast. We had to re-make this part and scrap an otherwise beautiful chunk of 1 5/8″ thick premium red oak.

Our mast has been drying too fast.

The mast I’ve been carefully planing down, and the same mast I spent the past day and a half sanding to get it exactly round. Rather than do a clever little build up about how great everything was going and then jerk the rug out with a picture of the cracking, I’ll just cut to the chase.

It’s been splitting right next to the seam. Our solution has been to fill the split with epoxy to stabilize it, but today two more splits opened up, and an old one almost doubled in size. I filled those too, but she desperately needs to be shellacked. I’ll do that tomorrow, but I wasn’t able to do it today because we had to wait for the epoxy to cure. Shellac will slow down the transfer of moisture across the cell walls of the wood and allow things to slowly acclimate (and not bust apart).

Here she is, sad little thing.

The check looks darker because it’s filled with expoxy right now, but that’s about a 3′ long check. I think we’ll be able to salvage it, but what a PAIN.

Prior to all this, I spent a good half day marking and planing down from 8 sides to 16,

and then 32 sides all before starting to sand it to its final round shape. That was a nice time, although working out the layout lines for 16 was harder than I’d thought. The layout marks Iinitially made for 16 sides turned out to not be as accurate as I wanted, so I had to work out exactly how wide each segment should be all over again, and then lay these out.

If people ever tell you that the geometry you learn in school is a waste of time, they’re wrong. Geometry saved my butt.

The initial way to lay out the lines should have been straightforward. After using the circles on the side to determine the width of the 16 sides, the idea is to take that information and transfer it over to the newly planed 8 sides with a compass. Observe:

Here’s an 8 sided mast (with a batten on top of it just to comfuse matters). You can see the initial layout lines there on the face that the compass is on. Above and below that face are the 2 faces planed down from the corners of the 4 sided mast, using the layout lines generated to make 8 sides. The batten is sitting on one of those newly planed faces. So, you set your compass to the width of the side defined by those 2 layout lines in the center, and then, with the point of the compass still on the layout line, swing the pencil end up to the newly planed side,

Like so, and make a little tic mark. Since each face on a 16 sided (or 8 or 32 sided for that matter) mast will be the same width, once you know the width of one face, you just need to copy that width all around the mast and you’ll have yourself some points to make layout lines from. Unfortunately, my initial layout marks we’re exactly equal, so I had to work out the exact side width, and then center these widths on each side. It was a slow process.

That batten in the above photo is there to connect the point I just made with another identical point farther down the mast. When done, you get long lines defining the edges of each of the 16 sides. You can see those lines in that photo above (here it is again)

See? this is what it looks like after you’ve planed an 8 sided mast down to each of the lines that defined an edge of one the 16 sides.

You can see how this formerly square mast is slowly becoming more circular. We do this by planing off the corners of the square, and then planing off the corners of the 8 sides… guess what we’ll do next? You got it. We’ll plane off the corners of the 16 sides to get 32 sides. You just have to do this in such a way as to produce equal width sides. See how each of those 16 sides are about equally wide? You want to do that next with the 32 sides.

The way to do that is to keep your plane perfectly centered on the edges you’re working on, and not planing more on one side or the other. With the sides up to now, we’ve been doing that by laying out lines defining the edges you’re planing down to. That’s too much work for 32 sides. Here’s another, much simpler, way to keep track of exactly where you’re planing.

Make an angled line on each face of your 16 sides, and then angle the opposite way when you reach a face edge. Each point of this Charlie Brown line rests on the intersection of 2 sides. Now, when you plane, try to split that line right at the point. You can see where I did that earlier in the 2 angled lines up to the right of the continuous line. Each swipe of the plane takes a little more off, so you can accurately track both how centered you are and how deep you’re going with your cuts. Plane a bit less than 1/3 of the line away, rotate your mast, and go to the next line. When you’re done, you’ll have a 32 sided mast.

You need those lines because the sides start to disappear in the grain pattern and it’s tough to know exactly where you are when you’re planing. Here’s the final result.

You can see the remains of the Charlie Brown line with the points planed off.

Next up, sand sand sand.

We use a thing called a box sander to do this. During a break in the action while Kev was working on a plank, I made a fancy one.

It’s really just a 3 sided box, with sandpaper stretched across the open 4th side. Some folks whipped them together in 15 minutes and band sawed out a simple handle, like a push stick, on the top. I made nice handles for mine as well as putting in a little system to clamp the paper on each side of the box. Most folks just stapled their sandpaper to the sides of the box. Granted, it’s way simpler, but it’s also a pain to change the paper (pull the staples, staple on a new sheet of paper) and the paper tends to rip out at the staples. Mine took a couple of hours to build, and then Shaun and Kev decided it had to be shellacked. Now it looks like an antique, aside from the drywall screws and plastic knobs on the side I mean.

To use the sander, you put it on your mast like so.

This allows the sandpaper to conform to the mast. It automatically sands the high spots more than the low spots, leading to a rounder shape.

The technique is to sand in a long, twisting stroke, like a screw moving up a threaded rod. This makes the actual sanding direction diagonal along the spar. The advantage of this is that you distribute any errors you might introduce through less than perfect pressure or whatever along both the length and girth of the mast. In other words, you’re spreading out your mistakes in such a way as to even them all out.

Like all sanding, you work up the grits as you get your high spots eliminated. Starting with 60 grit (quite coarse), you move up to 80 grit to remove the 60 grit sanding lines, then up to 120. You know you’ve evened out your high and low spots when you just sand away the last of your pencil marks.

The work is slow and methodical. Work your way up the mast, rotate the mast a tiny bit, maybe a 20th of a turn, and then work your way down. Repeat over and over. It helps to have the mast set up between 2 posts with a nice clear work area in between.

There are faster ways to sand a mast round involving a sanding belt and a drill to spin the belt around the mast, but it’s much easier to sand away too much material and create divots in your mast this way. I chose safe and slow, and it came out beautiful. Silky smooth and almost perfectly round… probably to within a few thousandths of an inch.

And then it started to blow up. So, I have lots of motivation to get in to the shop tomorrow and put some shellac on that puppy.

After our breast hook blew up, we made a 2nd one and shellacked that pretty quick.

While I was sanding along, Kev got to work fitting the breast hook into the bow of the boat. That was a tricky job, and it took all morning to get it right, but he did a beautiful job.

Oh, I forgot to mention that we got the sheer clamps installed. You can see them there. On the tops of the sheer clamps near the stem, you can see how the paint has been planed away. Kev did that to make a perfectly flat surface for the breast hook to sit in.

This is a tricky thing, because the breast hook has to fit up tight against the planking and the stem, while also resting flat on the sheer clamps. This means he had to bevel the sides of the breast hook to match the curve of the boat going both forward and aft AND as it curves down into the boat. That’s called a compound curve and it takes a lot of careful planing to get it right. Oh yes, and he had to keep the breast hook flat side to side and dead on center in the boat at the same time.

Hat’s off Kev.

That’s it for now. Film at 11. Hopefully our mast will be in one piece tomorrow when I go in.

This entry was posted on Friday, March 30th, 2007 at 10:04 pm and is filed under Classes. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.