Curvy little joints
I’m forever amazed at how tricky some of these seemingly simple joints are. That amazement tends to come after I’ve screwed up a piece and didn’t see it coming. There’s a big “HUH…” squinty eyed look, like the part has just told you something you don’t quite believe. What the hell, I measured you, I cut you accurately, what do you mean “I don’t fit??” That’s just crazy talk.
Everyone says that the tough thing about building a boat is the lack of right angles. Personally, I think that’s one of the most interesting things about it. In some cases, you can work out and mark the cuts you’re going to make ahead of time, and in other cases, you have to look at the part carefully and make little marks on it to guide you in what is essentially free-handing when you plane or chisel. Today was a little of both. Let’s start with the Carlins.
Ok, you totally saw that coming.
The Carlins are the longitudinal supports that attach to the ends of the short deck beams around the cockpit. They help support the little deck there. Just looking at them, you’d think, what a simple thing. You cut the piece to length, maybe bevel it a bit, and screw it to the deck beams. How easy is that?? Here’s the starboard carlin clamped above the short deck beams.
A few things are worth noting here.
- The carlin curves outwards to follow the curve of the boat.
- The carlin also curves upwards slightly as it goes fore and aft to follow the sweep of the sheer.
- The carlin also remains roughly plumb as it curves (the inner face stays straight up and down)
Since the carlin curves outboard, you can’t just sit the rough carlin on the boat and measure how long it is. The curve adds some length. Cut it by laying it out straight and you’ll be about 1/2″ too short. Also since it curves outward, the surface where it meets the long deck beams forward and aft are not 90 degree cuts. They’re beveled (you can see this by curving your fingers slightly and holding your fingertips against a flat surface… they don’t meet at 90 degrees), and you have to figure out what that side-to-side bevel is.
Since the carlin curves upwards as well, there’s also a top-to-bottom bevel that has to be taken into account.
Since the carlin ends up plumb, you have to keep it plumb when you pre-bend it to work out your bevels. The carlin is resting on curved deck beams both fore and aft as you’re doing this (you can sort of see that in the above photo) and it doesn’t Want to stay plumb. It wants to sit on the curve of the deck beam. Also, bending the carlin in 2 directions makes it want to twist out of plumb.
Now we’re having some fun, eh?
The solution to all this bevelly mess is to do your layout carefully. You don’t really get a 2nd shot. If you cut it too long it won’t fit in. If you cut it too short, well… you’ve cut it too short.
Warning: geeky boat technique stuff ahead, really only interesting to people who are trying to do this stuff themselves.
Here’s what I came up with (thanks Jen for some excellent suggestions) to do the layout. We’re now looking forward.
You can see there are 3 Jorgenson (wooden) clamps spaced along this clamp up: 1 at each end and one in the middle. They’re set up to be plumb, and thus give the uncut carlin a plumb surface to register against. That keeps the carlin properly upright. They’re also set up so that when the carlin is pulled up against them, the bottom edge of the carlin just rests exactly above the short deck beams that they’ll eventually be screwed to. You can see there are 2 orange clamps pulling the carlin into position about 2/3 along its length. Turns out I only needed those 2 to get everything pulled into alignment.
So, now we’ve got our carlin in the proper bend and plumb, right above where it will be installed. To get the side to side bevel is now easy. Take a pencil and run it along the edge of the deck beam beneath the carlin and you’ve got that bevel. Take a straight edge and hold it against the face of the carlin and down against the deck beam, and you’ve got your up and down bevel. This is something better seen than explained in words, but trust me, it works. Ok, the 2nd line will be a pencil width long from where you need to be, and the first line will be a pencil width short, but you probably already figured that out. Cut the 1st one fat, and the 2nd one tight and you should be fine.
End geeky part.
The 2nd really tricky joints today involved putting in the short deck beams that attach to the mast partner. Remember how I said earlier that the mast partner and mast step were made to be extra strong? Here’s some more of those supports.
You can see the 2 short deck beams notched into the red mast partner on the starboard side here. This is an extra fun joint. If you look at how it notches into the sheer clamp you can see all kinds of bevels.
- The sheer clamp tilts outwards, so you have to get the top and inboard angle to match.
- The sheer clamp curves in towards the bow, so you have to get that angle right.
- The sheer plank also flares out and curves inward.
- The notch in the mast partner is an angled ramp that goes from nothing at the bottom to 3/4″ deep at the top
- The beams should be plumb.
Whew. Just for fun, here’s what the part looks like when it’s done, leaning up next to the ramp cut.
By the time I got around to these guys, they were in fact pretty easy. The trick, again, is to get your beam clamped in place so that you can mark it accurately for all your cuts and bevels.
I’m not even going to try to explain how you do those. If you’re dying to know, I’ll make up a series of photos. Suffice it to say, that it’s really satisfying to have it all glide together like a Chinese puzzle.
It starts out in the notched ramp
And as you press it down, the ramp slides it outboard
So you move in towards that joint for the sheer clamp both vertically and horizontally
and if all goes well, it just slides right into place
Voila! Perfect fit in the slot, the sheer clamp, and against the sheer. Sheesh. Sweat sweat. The thing is, when you’re done, it just looks like, “Ok, you’ve got a little chunk of wood attached to the mast partner. Big Whup.” In fact, this whole thing will be completely hidden by the deck in a week and no one will ever see it again. But now you know and I know. It’s like a little secret, only published on the Internet.
One trick for making joints fit perfectly is called “kerfing” and I may have mentioned it before. Kev built the Strongback the other day and it also needs to fit solidly to the yoke. Unfortunately I don’t have any good photos of it, but here’s what it does: It goes from the top of the centerboard trunk, just under the deck beams (they actually rest on the strongback), and up against the aft face of the yoke. Kev didn’t get the bevel exactly right at the yoke, so we kerfed it.
Kerfing is the process of running a saw in between 2 imperfectly fitting surfaces. The saw cut evens out both surfaces so that they mate up just right. You can see here how there’s a slight gap at the bottom of the strongback / yoke joint. Kev is kerfing the joint with his Japanese saw.
Working it a little more….
Here’s the resulting fit:
Not too shabby. There’s a tiny tiny gap at the bottom, but we can live with it.
The last fitting looked like it was going to be a cinch, but it wasn’t. These parts are called Coaming Knees. In a boat, a knee is a curved piece that supports something else. Boat builders will search around for old tree stumps and curved branches to find wood that’s naturally grown into the curved shapes that they need. These are the strongest ways to make a knee.
Our coaming knees don’t have to be super strong, so we just cut them from pine. Here’s one:
The real function of this part is to provide a nice curved surface for the cockpit coaming to rest up against as it curves in from the carlins to the aft most forward deck beam. Now, the carlin and that deck beam are both plumb, so it should be simple, yes?
No no no. You saw that coming too.
The carlin is plumb, yes, but it CURVES. Take your left hand, cup your fingers in slightly. Take your right hand, hold if flat and press it against the cupped left hand. Now angle your right hand up slightly. You’ll see that you’ve got 2 places where your hands contact each other: at the top edges at the fingertips and heels of your hands. In order to make that knee fit flush against the carlin, it has to be planed in such a way that you get a curve running front to back along with a rolling bevel from top to bottom. I could find No Way to map this one out ahead of time, so I just did a series of fittings and minor adjustments until everything fit well. Thank god we’re working with pine here. Oak would have been a pain, particularly since it’s all end-grain planing. I’m happy with the fit, however.
It had to be a good fit since it gets attached with screws and yellow glue. Yellow glue has lousy gap-filling properties. It likes a nice, close fit.
If you don’t have good 3-D visualization skills before building a boat, I’ll bet you get them by the end.
Doing things like fairing out the deck beams has been a walk in the park compared to all that fussy fitting. It’s pretty straightforward: take your deck camber template, lay it next to a deck beam, mark the camber, plane to the mark. Here’s the camber template with a vertical post set up to register against the center line string.
And here’s a close up. You can see the pencil mark from scribing the camber on the forward edge of the deck beam.
Do the same thing to the short little deck beams that attach to the carlins. This photo was made before I attached the carlin. The forward beam has been marked and planed, the aft beam has just been marked.
I’ll bet you wish I just put in some George Carlin jokes instead of all this fiddly stuff about joints, eh? Maybe next time.
On the lighter side, I brought my remote controlled electrical outlet back from Madison for a little magic tool fun. It’s normally used to turn on your dust collector remotely so that you don’t have to walk across the shop every time your use your stationary tools. However, in this case, we hid it and hooked it up to the band saw by our bench, and had it suddenly start up when folks walked nearby.
NOTE TO OSHA: This was not done in such a way as to endanger people. Come on, how stupid would that be??
Of course, folks would stop and look, and then I’d turn it off remotely. They’d look around, and we’d say, “Yeah, it’s been doing that all day… go figure” and give it a little kick. It’d start up. Kick. It’d turn off. One guy gave it a couple of kicks and we suggested he be nicer about it, and maybe apologize to the saw for kicking it. He apologized, it turned on. He kicked it, it turned off. After a while we had quite a little crowd all trying to figure out what in the world was wrong with the saw. Of course, once it started responding to voice commands the jig was pretty much up and it was just a lot of experimentation trying to figure out what kind of commands the saw would respond to.
Shop fun. It’s not for everybody.