A Shipwright in Training

This past week I got to play with metal.  Wow, this is cool stuff when it doesn’t burn/cut/poke/shoot sparks at you. 

More on that in a bit. 

Just when you get your head ready to do something, it’s helpful to stop said head and scratch it.  Is there anything that Must Happen before this process?  In the case of installing the deck, the answer is, “yes, yes there is.”  Here we’ve got the beams faired, the covering boards are on, the decking is cut and varnished on one side… seems like all systems are go.  But wait, after the deck is on, we’ll put canvas on.  And where does the canvas go?  Into a little dado along the covering board.  And how will that dado get there?  We’ll rout it in, using a fence running along the inner face of the covering board.  So, since the decking gets installed starting from that same edge of the covering board … gotta do the dado first before the decking gets in the way.  But wait, there’s more!

We’ve been getting some updates from the folks who are designing the rig for Madcap and one of the things that they wanted was a pair of running back stays.  These require some serious fastening in the aft end of the boat, and luckily, we haven’t put the deck on yet.  Installing these suckers would have been impossible if the deck was in the way.

So, let’s get the dado done.

There we go.  One long groove carefully routed into our beautiful covering board.  This was a bit nerve wracking because one slip with the router and the covering board is seriously hosed.  An electric tool can make mistakes much faster and nastier than most hand tools ya know.

The limitation of the router setup is that we have to stop for obstacles. 

The chain plate, for example.  Can’t fit a router next to that puppy.

Or the corner at the transom.  The solution of course, is to batten out the path of the dado and cut the missing segments in by hand. 

That light strip of wood being clamped down is a batten that will be used to connect the dados in a nice, fair line.  Do that for both sides of the dado, and you now know where to cut your dado.  Chisels and a saw should do the trick.

The dado is there to hold the edge of the canvas decking by the way.  We make a T-shaped toe rail that traps the canvas in the slot.  Here’s a mock up.

The toe rail will be low with a slight rounded surface on top.  The original boat just had a strip of wood holding the canvas down that was flush with the covering board as far as we can tell.  We’ve decided that a toe rail is better.  It gives a more finished looking edge I think.

So, metal smithing.  This was a blast, and I want to do it more.

The task was to take the designer’s drawing of a metal plate called a Swallowtail, and fabricate it so that it fit snugly to the frames and sheer clamp.  The running backstays need a lot of support, and this distributes the load across 2 frames and the sheer clamp. 

The process of fabricating this was pretty simple really.  I scaled up the swallowtail from the design plan, and made a paper template.  Then I fit the template onto the frames to make sure that it would actually fit the real boat (as opposed to the ideal boat drawn in the designer’s computer).   Once I tweaked the template to where I thought it would fit, I xeroxed 2 copies of it, cut them out, and spray glued them to some sheet steel we had in the shop.  This way I had a perfect pattern right on my piece to guide me when cutting it out on the metal-cutting band saw.  Easy, yes?  Of course.

Next step was to bend the cut out parts to fit up against the frames.  I patterned out the the frame shapes and used these to guide me as I bent the steel.  Bending the steel?  Yes, with my teeth, like any good bodybuilder.  Yaaah!  More Steroids!!!

Ok, not true.  No steroids.  But this thing is a bottle jack on steroids.

This jack presses Down, instead of up. Ok ok, it pushes both Up AND Down at the same time, but it only can move in a downward direction so the net effect is that it pushes down.  Lord.

My silver sheet metal is being pressed down by the rod welded to the vertical steel plate there.  You can just see that the sheet is resting on one edge on a thick piece of copper stock in the back.  When the rod presses down in front of that copper, the sheet metal bends up.  This gives it a little curve.  Do this along the face and you get a nice curve to your piece.

Here’s the plate with the paper template still glued on, and a curved tempate of the frame next to it.  If you get too much curve, just hammer the plate out flatter on the anvil.  Wear your hearing protection… yow!

There it is getting flattened out a bit.

So, the process is simple.  Bend, check, flatten or rebend… use a ball peen hammer to ease any sharp bends, and voila!   Check your fit to the actual frames until it’s just right.

Next, we weld a couple of side pieces to either leg of the swallowtail.  This stiffens and strengthens the piece.

We used a mig welder similar to this one.

It’s way cool.  The welder uses electric current to make the super bright/hot arc that melts your metal.  At the same time it feeds a thin wire into the weld site to add metal to the weld.  It also blows an inert gas on the weld site to force oxygen away and stop the metal from oxidizing as you heat it. 

Let me just say, I bite at welding.  Sure, I can make welds that are strong, but they look like hell. 

A good weld looks like an even series of tiny ripples that run right down the seam.  Mine look like a lava flow.  Still, it’s my first few times and I expect that practicing a few thousand times will yield some improvement. 

Another thing that’s cool about welding?  The mask.  I thought the little window you look through while you’re welding was just very dark glass.  In the old days, that’s exactly what it was.  But these are modern days, bucko, and everything modern is better. 

Nowadays, the glass you look through is electrically powered and light sensitive.  When you look through it in normal light, it’s like looking through dark green sunglasses.  As soon as a bright light hits the lens, it darkens almost instantly to a level that allows you to look at your arc safely.  When you stop using the arc, it lightens up again.  Way way cool.  The fancier helmets even allow you to adjust how much light triggers the lens and how dark it gets. Nice.

So, now we’ve got this part that fits over the frame with side braces to stiffen it.

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That’s all well and good, but we still don’t have a way to attach this thing to the running back stays.  Right now, all this is good for is sitting on top of the frames.  We need to weld a plate across the top of this piece that will go underneath the sheer clamp.  The back stays will bolt down through the covering board and sheer clamp and into that plate.  The trick is to get the angle of the plate just right, so that the swallowtail is flush against both the sheer clamp and the frames.  We get that angle simply enough by placing the swallowtail up against the frames and measuring the angle directly.  Now, the tricky part is holding the plate in place at this exact angle while we weld it.

Not so tricky if Lew is your teacher. 

One of the cool things about working with steel is that it’s iron-based.  That means you can use magnets to clamp it in place.

The big red magnets hold the plate in place.  The plate is identified with the blue arrow.  You can see that the top of the plate is up against the magnet, but the bottom of the plate is held away from the magnet by a piece of scrap steel (green arrow).  The scrap transfers the magnetic attraction, so it holds the bottom of the plate away at just the right angle.  The vise grips (behind the blue arrow) then clamp the whole thing down tight.  A couple of spot welds and you can remove all this stuff and just weld away. 

This is easier than woodworking.  Sort of.

Once it’s all welded up, I grind down the welds to make them look pretty and fit it in the boat.

Not too shabby! 

Next trick is to drill holes for the running back stays.  The back stays are a pair of U-shaped bolts that go down from the covering board through the sheer clamp (with blue tape on it above) and into that plate we just welded.  The task is to drill them very precisely so that the legs of the U are parallel, they start in exactly the place you want them to up top, and they end in exactly the place you want them to under the sheer clamp.  Sounds hard.

Jig Time!!  Thank you Warren, thank you Lew.

Once again, a good jig makes a hard thing easy.  This little jig allows you to drill a hole to a precise location. 

Here’s how it works.  I attached 3 chunks of oak to this scrap cedar board, and drilled a 3/8″ hole straight through the 2 chunks on the left there.  These 2 holes now guide my drill bit towards the 3rd chunk, protruding right below the cut-out in the cedar. 

I drilled down to that 3rd chunk and just touched it with the drill bit to make a dimple.  Now I know exactly where my drill will end up when I guide them with the 2 holes.  I then put a little nail in that exact location, clipped off the head, and sharpened it to a point. 

The cut out is there to allow this jig to go around the thing you’re drilling through.

Now, all I need to drill exactly the hole that I want is the location of the entry and exit points.  I know that if I put the nail in the center of the exit point and start the drill at the entry point, the drill will go exactly to the tip of the nail.  How cool is that? 

Yes, very cool.  I know.  Yes, it’s cooler even than wearing your boxers way out above your low low pants.

I worked out the entry and exit points for the U bolts, and it turned out that they’d go right into the dado we made earlier.  This was actually pretty handy.  I made a stick that fit snugly into the dado, marked the entry locations, and drilled small starter holes in the stick. 

You can see it there below my hand.  I copied the spacing of the holes to a strip of blue tape (remember that tape that was on the sheer clamp above?) and stuck it to the lower edge of the sheer clamp.  This gave me the location of the exit fore and aft.  I knew I wanted the holes to end up in the middle of the metal plate, and the plate was 1 1/2″ wide.  So, I set the exit hole back 3/4″, and now I had the inboard-outboard dimension to locate my pin.  Stick the pin in that location, start drilling in those entry holes, and zowie!  A perfectly aligned hole. 

[See why the deck couldn't be installed by the way?  I made the opening in this jig extra large in case I wasn't able to start this until a few strips of decking had been installed.  You can see the first strip of cedar decking, in fact, installed just to the left of the mahogany covering board.]

The nice thing about having the stick with the holes in it is that I can then take it over to the other side of the boat and place it in the dado there, and voila!  I have a perfectly matched set of holes for my back stays on the other side of the boat.  So simple, so precise. 

To mark the holes locations on the top plate of the swallowtail, just hold the swallowtail against the frames and sheer clamp, take the drill out of the jig, and drill down through the nice holes you just made.  This puts little dimples in exactly the right locations on the top of the swallowtail.  You can then drill these out more easily outside of the boat.

Now, you may be saying to yourself… why are you using steel here?  Steel rusts!  And if you knew that the U bolts were bronze, you might be appalled.  Everyone knows that electrolysis is a big problem when you put dissimilar metals in contact with each other.  That’s what I thought anyway. 

The answer is… yes electrolysis is a big problem, but only when there’s something to act as an electrolyte.  Like salt water.  These parts will be high up in the stern of the boat and should not get very wet.  As a precaution though, we’ll be painting the swallowtails with epoxy paint to protect them from the elements.  The knees in the boat are steel, and they’ve been there since 1924.  As long as they’re not constantly wet with salt water, and protected from corrosion, they should be fine. 

Next up, making the nifty little U bolts.  Stay tuned, same boat time, same boat channel.

This entry was posted on Thursday, April 24th, 2008 at 8:10 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.