Keelson, Strongback, Transom

Strongback

As Spring finally arrives in Brooklyn, I’ve had the opportunity to finally finish setting up the strongback and molds. Our backyard is concrete, lumpy and sloped to a center drain, so leveling the whole thing took a bit of work.

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Setting up the molds was pretty straightforward – I had milled a center registration hole through all of the stations, so I could line them up with the laser. I confess I was amazed when I sighted through the hole at the stern and could see all the way through to the bow station.

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Finally, my son and I managed to pull the keelson assembly up from the cellar, and “offered” it to the molds (a favorite phrase of Mr. Oughtred). The fit is too close – the one mistake that I made with the precision-cut parts was to make all the cutouts exactly the width required. This came into play with the notches in the stations that sit over the strongback – that level of precision is just too precise for something built out of exterior-grade plywood and stud-grade lumber. I’ll open up the notches today and make templates which line up the inner stem and the transom.

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Mast and Spars

Small parts

I’ve been working through some of the small fittings required for the Tammie Norrie and her rigging – I have a couple of flatsawn rough white oak planks that aren’t clear or straight enough to piece together into larger objects, but can be milled into smaller fittings. The white oak is quite well seasoned, and mills nicely:

A two-piece half of a gaff jaw:

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The upper piece of a deadeye lanyard (the standing rigging will all be Dyneema 12-strand):

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Boatbuilding, Transom

Transom Trouble

The next part to be cut was one I had eagerly anticipated, the solid mahogany transom. I found a large piece of reclaimed 4/4 mahogany trim and managed to extract all of the square-cut nails embedded in it, and glued it together into a suitable blank for the transom. This is the one piece of the boat I am definitely hoping to finish bright.

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I started by planing or facing the blank down to the specified 7/8″ thickness – this also allowed me to remove the varnish left over from the finished side of the molding and the rough saw marks from the backside. I then set about milling the transom to shape.

Transoms are tricky pieces of three-dimensional geometry. The Tammie Norrie’s transom is angled gracefully back, and meets the planks sweeping up from the front of the boat. In addition, the top of the transom wants to be level, so it gets beveled in the opposite direction.

Everything was going fine, until the machine hit some bits of square nail that I hadn’t found. Now the metal in these nails is soft enough that the carbide end mill can cut right through them, but the machine and the blocking holding were not rigid enough to hold the transom blank. I thought I had managed to put everything back into place, but after hitting and removing two more pieces of nail, I realized that the blank had shifted too much to continue. I invoked the “three strikes” rule, and went to bed.

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Ouch. Ouch! OUCH!!!

The next night, I decided I would re-align the machine to the blank, and fill the portions that had been inadvertently removed with epoxy thickened with mahogany sawdust. After letting that cure overnight, I set to milling again.

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Fortunately, most of the filled areas will be covered up by the planks. A few places will be visible – I can only hope that the epoxy matches the mahogany well enough that they wont be glaringly obvious. I’m pretty pleased with the finished transom, despite the goofs – the well-seasoned mahogany machines like a dream. My plan is to coat the whole thing with epoxy before varnishing – its not ideal, but it will be outside for quite a while before it gets finished.

IMAG0592IMAG0604Inside baseball: I moved the sculling notch to the port side – I’m hoping to be able to move the boat around the docks by sculling, and all the pro scullers seem to recommend moving it to port. I’m still not sure what one does with the boom if one is standing and sculling.

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Uncategorized

Milling the Apron

With some trepidation, I’ve started on the first big test of this building method – making the inner stem. I suppose making things on a CNC mill is a big time-saver if you have a big-iron mill with automatic tool changing, and you’re making repetitive parts out of consistent stock. This project has none of those aspects.

I decided to start with the inner stem, or apron – its not a part that requires a high level of finish, and most mild screw-ups can be hidden between the outer stem and the planking. It does require, however, a two-sided multi-step milling setup, and the two sides must be precisely symmetrical (if nothing else). Starting to see why picking up a chisel and just whacking away at it is faster?

I’ve given up on reclaimed wood for the backbone of the boat – I briefly entertained laminating and scarfing pieces out of 3/4″ white oak plank, the best I’ve been able to find around me in Brooklyn. The alternative has been hunting through the Structural #2 and Better at the big orange box – I’ve managed to find a few 2x10s and 2x8s with enough clear, tight-grain material to make the stem and keelson – we’ll see what happens after that.

The key with planning a milling setup, I’ve found, is to crowd out operator and material error. The machine is very accurate in relationship to itself, but the moment I start relying on my own measurements the inaccuracies start to multiply. The answer is to always have the machine making the jigs as well, and checking the machine position against the digital model along the way.

I started by cutting the three pieces of the inner stem out. Let me be clear – the puzzle joints of these pieces are nowhere near what an accomplished carpenter could make on a bandsaw. They are, however, just about accurate enough for a nice juicy epoxy joint (between 1/16″ and 1/32″). I also cut a caul that would serve as the final shaping jig. This is a technique that I found in a book about making archtop guitars – basically, a female jig that holds the male part exactly while it is being worked on. The caul also ensured that the final glued assembly would match the intended shape and dimensions – it also happened to be the perfect amount of clamping pressure for the epoxy joint. The addition of packing tape underneath the piece was enough to create a nice snug fit for the gluing operation.

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Setup for gluing in the routed ‘caul’

Not tight enough for furniture, but plenty of room for epoxy

Not tight enough for furniture, but plenty of room for epoxy

After the glue dried overnight, I planed off the excess glue, and reset the stem blank for the next shaping pass. The important purpose of the caul (despite its usefulness as a gluing setup), is that it accurately locates the piece on the mill work surface for further operations. After a roughing and a surfacing pass, I had one side cut to the appropriate rolling bevel. To save some time, I chose not to surface the piece completely smooth – I figured a bit of “tooth” would be good for the epoxy.

The roughing pass

The roughing pass

Not bad!

Not bad!

The second side was a bit more challenging – I had left two flat areas to the piece would sit level when flipped over (with the first cut face down), but I also needed to cut a mirror-image caul. I discovered when I clamped the piece in the new caul that it required a bit of leveling to make sure the uncut face was completely level. In the process of clamping it down with pits of MDF, I inadvertently discovered what I will call “MDF cam clamps” – basically, a small block of MDF is set against one side and screwed down to the work surface with a single drywall screw. When the piece has been thus clamped from all sides, I discovered I could tap the MDF slightly to the side to tighten everything up – the MDF is soft enough that it will deform before marking the stem.

The rough final finish is visible here. With 45 minutes (more passes), this would be quite smooth.

The rough final finish is visible here. With 45 minutes (more passes), this would be quite smooth.

MDF Cam Clamp

MDF Cam Clamp

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The second side went off without a hitch. Now on to the keelson!

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Boatbuilding

On Lines, Drawings and Models

As an architect, I am always fascinated by boatbuilding plans, and the prints of the “Tammie Norrie” design are no different. I love the coherence of lines plans, how the design is all present and verifiable from the drawings. I also like the economy of the drawings, how each piece of timber, each profile is specified just once, and things that Oughtred thinks should be left to the builder are not called out (from the work of other designers I have looked at, Iain seems to be one of the more relaxed about the capabilities of the builder).

From the start, my plan has been to create a 3d model of the boat, and build or design parts from that model. I have yet to start cutting the planks, but the stations have all been cut from the Rhino model I have been building. As I started to “build” the boat in three dimensions from the plans, I quickly realized that I would have to do a certain amount of fairing of the points derived from Oughtred’s station drawings. Whether this will be successful or not remains to be seen.

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Boatbuilding, Transom

Transom

I was at a loss for what to build the transom from – Iain Oughtred calls for 7/8″ stock, which is just a little more difficult to find than 3/4″ – he’s really asking for 4/4 planed down to size. I finally found a hefty plank of mahogany – one side was varnished, with a bit of a latchset still in it. The opposite side still showed marks from the saw mill – it looked like it had been saved from a nice old door frame, maybe from a pocket door, and was a solid 1 1/4″ thick.

IMAG0353Using the CNC mill, I carefully planed the edges of the boards true and fashioned a jig from a piece of MDF covered with packing tape (so the epoxy wouldn’t stick to it), and a shim to get the boards nice and snug. Though its not immediately clear here, I flipped the boards alternate directions so the grain pattern would alternate.

I managed to get good glue coverage and nice uniform glue lines – the next step will be to use the CNC to surface the transom blank down to the specified 7/8″ thickness.

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Boatbuilding, Mast and Spars

Wood

Except for two packages of marine plywood I ordered from Massachusetts, I’ve been sourcing most of the wood for the boat from Build it Green, a local material reuse/recycling center near our house. I suppose I haven’t found a good local lumber yard in Brooklyn yet.

In order to find suitable lumber, I find I have to visit BIG weekly, to the consternation of my spouse and kids. It is also lending a certain serendipitous quality to the boat, which is being pieced together from the best I can find. Case in point – I found two beautiful Douglas Fir joists, tight grained 3″x8″s with nary a knot or check between them. Though I am reluctant to do so, I am slicing them up to laminate and scarf together the mast and maybe a spar.

It has also resulted in at least one screw-up, as when I bought a handful of oak planks (formerly library shelving of some kind), only to find that they were red oak under the finish. They will eventually become furniture (or shelving), but not part of this boat. As I found out, red oak (unlike white oak) is extremely porous, to the point where it can be used as a straw. If I can’t find something more suitable, the keel and stem will end up being Select Structural DF from the Big Orange Store.

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DF FTW!

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The horror!

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