2015-05-14

Post XXX - (The sexy one!) Homemade Bevel Gauge, More Gunwales, Knee Templates

(small edit) frigged up the roman numerals on my post titles. This one is now XXX!!! SOO SEXY ME LOVE YOU LONG TIME

I am getting into the finish work on the boat now. Harry Bryan and Wyatt Lawrence's boatbuilding basics course last year gave me some good training on how to proceed with the knees and breasthook, and the complex bevels required to make them fit the boat. All of these pieces are going to be attached with mechanical fasteners only (in case they need to be replaced down the road), so it's important that they fit right. 

The primary measuring tool used for this purpose is the bevel gauge. I have a cheapo Canadian tire gauge but it is far too big to use in confined areas, and much too clunky for tranferring bevels to paper. Luckily, Harry has a book out on how to go about making a much more conveniently-sized gauge -- link:


Harry's book shows how to make a single-blade gauge and a double-blade gauge (pic from Harry's book in Figure 131) from a few pieces of brass sheet and a couple of copper boat nails. I chose the double because I'll probably only make one gauge for the time being. Size of the blades is pretty much arbitrary and you can make one as-needed for virtually any size & length within reason. WARNING: this takes a lot longer than you think it is going to!!!

Figure 131: The goal - from "Making Hand Tools", by Harry Bryan


First order of business is to cut the stock. I'm sure sensei Harry built his out of scrap brass and old nails, but I don't own a *real* boat shop yet so I bought materials new, figuring I could use a bunch of it for protective coverings on high-wear areas of the finished boat.

I marked a 5/8 line parallel to one edge and started sawing with the hacksaw. This is naval brass --harder than regular utility-grade brass -- but is still pretty easily cut using a hacksaw. About a half hour later I had 3 strips at 12" by 5/8" by 1/16". These were then cut to length, including the 45deg angles on the ends of the blades. 

Figure 132: Cutting carefully along the line


Figure 133: Brass bars 


The procedure for riveting the pieces together is a bit fiddly and it took me more than one attempt to get it right. I'd recommend anybody trying this to experiment on a few sacrificial pieces first. Also buy Harry's book as it describes this all in quite a bit more detail. 

Preparation:
  • Cut plate brass to rough size and shape. Careful hacksawing with a new blade can be very accurate.
  • File the pieces to get at least one flat reference edge on each from which all measurements will be taken
  • Remove all burrs that might keep the pieces from lying against each other perfectly flat. 
Measurement (First pin on the longer gauge blade):
  • For a centred pivot, mark a spot 5/16" from the end and 5/16" from the flat reference edge.
  • Check the measurement 15 times at least, maybe 20
  • Take a punch and give the marked point a good thwack with a hammer to make a dent.
  • Check the accuracy of the punched dent 15 times. It has to be perfect or you will be in for a lot of filing work later
Machining:
  • Measure the copper rod that will be used to make the pivots. 
  • Pick a drill bit of the same diameter
  • Clamp all 3 pieces together, taking care to line up the reference edges.
  • Very carefully drill out the pivot hole, taking care that the drill bit starts true on the punched dent.
  • Use a countersink bit to put a *very* shallow bevel around the edge of the hole on the outer two pieces of brass
  • Unclamp and remove all burrs again. 
Riveting:
  • Cut a short piece of copper rod, 1/16" or so longer than the thickness of the 3 brass pieces put together -- this is your rivet. 
  • slide the rivet into the holes. It must be a sliding fit, but not so loose that it wiggles.
  • Holding the three brass pieces together tightly, peen the end of the rivet on one side slightly while holding it against an anvil or some other heavy unyielding surface 
  • Peen until the end of the rivet is rounded and big enough to fill the slight bevel created by the countersink bit. Light taps
  • Slide the peened end tight to the bevel and flip the piece over. Peen the other side in the same manner. Light taps 
  • Now start giving the rivet good hard taps on top to seat it. Tap once or twice and check the tightness of the pivot. It's easy to get it too tight.
  • Continue tightening until the blade rotates and holds position without support (you can always tighten it more later).
  • tidy up the peened ends using light taps. They will round out and fill in the bevel. 
Additional steps:
  • Repeat the drilling and riveting procedure for the shorter gauge blade. 
  • Same again for the spacer piece (shown in Figure 134), except use two rivets of smaller diameter here. Tightness does not matter on these...just hammer them in
  • Use a compass with 2 needles to scratch circular arcs centred on the pivot pins. Round the ends down to these lines.
  • Pull the gauge blades OUT and file thumb grooves.  
Finishing:
  • File, scrape, and sand away all bevels using 220 grit sandpaper (wet/dry works awesome). 
  • Sand the gauge blades really well, and round all sharp corners on the tool, on the blades, within the slots, and around the ends. 
  • Keep sanding and smoothing with 400 grit until things start to slide together nicely. 
  • A bit of trumpet valve-oil or sewing machine oil can be added to the pivots if they are a bit sticky. 


Figure 134: Gauges added, still needs the centre spacer.


Figure 135:Centre spacer in place, and thumb grooves filed out. Small bevel shown


Figure 136: Aaaaand showing the big bevel. 


That gauge took 1.5 boatbuilding sessions. I am proud of it, but glad to have it out of the way. 

We had a couple evenings of good weather so I took advantage to do some milling outside where I don't have to be bothered so much about dust. I resawed some ash stock to form the inner gunwales (1" x 7/8" cross-section this time). These were scarphed at the midpoint and glued with epoxy + adhesive filler. Note: I left the gunwales very long on purpose (about 3' longer than necessary) so that there would be plenty of room to stagger the scarphs on the inside and outside parts. I don't think the epoxy is so weak that it matters strength-wise, but it would look bad to have them in the exact same spot I think. 

Figure 137: Inner and outer gunwales all ready to go -- up out of the way



Finally, I built templates for the reinforcement pieces -- the gunwale-transom knees, the breasthook and the keel-transom knee. These were made by picking up angles with my bevel gauge from the boat's hull and transferring it to bristol board. The layout I've chosen below is deliberate too -- grain should nominally run on diagonals to the corner being reinforced. It makes for more wasted wood, but much greater strength in the knee.

Figure 138: Knee and breasthook templates laid out on stock


The figure below shows the joint I intend for joining the inner gunwales to the knees/breasthook. It's not strictly necessary to do it this way, but I think it looks a lot better to have a lap joint of this type. The 4" long slot with rounded ends shown right at the edge of the bristol board is the aft-most scupper in the inner gunwale. These are a good feature to include in the inner gunwale because it makes it easier to dump all of the water out of the boat when you turn it over.

Figure 139: Closeup of the knee layout where it joins the inner gunwale. 



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