2015-05-27

Post XXXII - Knee Fastening

This session concerned mainly the addition of gunwales, fastening of knees and cutting of the joints where the two meet. 

=============ASIDE ON FASTENING=================

Had a good discussion about screws vs. gluing gunwales on the woodenboat forum. The internet at large is split on this issue. Some say "glue glue glue", some say "both screw and glue" while others say "screw in case you want to remove and repair the gunwale". On the wooden boat forum (the opinion of whose members I tend to value highly), the general consensus was that "glue is how the designer specified it, so glue it must be". They also had grave concerns about anything that might penetrate the cedar core and allow moisture inside. Gluing obiously requires no penetrations, and is far less likely to cause wood decay or delamination. 

That opinion makes a lot of sense to me, but at the same time I really like the look of the gunwales being "buttoned up" with screw heads showing. Whatever...I just do. So I decided that I am going to both screw and glue these in place. Glue along the entire mating surface will effectively seal out moisture, and the screws (if predrilled) will help me clamp it down as I assemble and avoid me making a messy job of it. 

I also don't have enough clamps to do a good job!

The other bonus is that the fasteners will provide a lot of extra holding power and will avoid me needing fillets for the gunwales. I find the fillets look like absolute shit...so I want to avoid them wherever I possibly can. Screw and glue it is!

==========END ASIDE==================

The outer gunwale is a straightforward thing to add. Just clamp in place, put the knee inside and fasten it with screws. I did the same at the bow and stern to hold the 2 ends of the outer gunwale, then repeated for the other side.

Figure 140: Transom gunwale joint, starboard side


Figure 141: Transom gunwale knee screwed in place


Figure 142: Repeated on the portside


=============ASIDE No. 2: NOTE ON BOAT SCREWS===========

These things cannot just be driven into the wood without splitting it. Maybe on cedar, but certainly not on hardwood. Predrilling also makes the teeth grip better since they're not pushing wood grain out of the way as they bite in. You need 3 drills here.
  1. One countersink bit with a pilot drill the same size as the inside diameter of the screw threads. 
  2. One long pilot bit the same size as the countersink pilot. 
  3. One clearance bit the same size as the outside diameter of the screw threads. 

To set a hole for a screw, start with the countersink and make sure the angle is right. Sink as needed for a flush screw head or a subsurface screw head. Swap to the long pilot and follow that hole to get the full depth (nominally the length of the screw). Finally, swap to the clearance bit and bore the outermost pieces of wood (in this case my outer gunwale + hull thickness). 

Now when you sink the screw you won't split wood, it will draw the outer pieces of wood onto the inner piece, it will give maximum holding power, and you'll have a minimal chance of twisting the head off the screw. 

================END ASIDE No. 2========================

A couple of quick zips on the bandsaw and my knee / inner gunwale joints are made. The transom knee joint will have the aftmost scupper built in. This was repeated for the breasthook, though I did not cut that scupper yet. I discovered one unplanned-for issue at the bow: I didn't arc the breasthook -- it goes straight across the boat.

Figure 143: Notch for the aft scupper and joint with the transom gunwale knee


The flat breasthook means that the angle of the inner gunwale needs to roll from the flared angle of the hull near the bow to something that goes straight across. I gave myself 3 feet of gunwale to make the roll. I just took the required bevel angle off the breasthook where it meets the hull, and put the same angle on the inner gunwale. Maximum bevel is where the gunwale-breasthook joint is, and minimum angle 3' back from that. Offending wood was shaved using a plane and presto! It fits perfectly. 3 feet seems to be about right too; it's gradual enough to bend without steaming, but noticeable enough that you might think the builder knows what he's doing!

Figure 144: Rolling bevel for the inner gunwale and breasthook gunwale joint


Figure 145: Completed starboard side assembly at the bow.


My decision to glue AND screw was a good idea in the rolling angle too. Acute angles like that are very hard to clamp tightly. The screws do a much better job than clamps of pulling that bevel right around so it meets the breasthook flush. 

Figure 146: Completed starboard side assembly at the stern. Also, boats make good junk storage!


2015-05-20

Post XXXI - Knees & Breasthook Fitting

This was a really fun session -- getting otu knees and cutting bevels. First order of business was to cut the pieces out of the stock (shown laid-out in post XXIII). This was done using my crappy bandsaw. Careful slow cutting with the bandsaw avoids a lot of planing and adjusting work later on. The transom knee has no complex bevels, so it fit right out of the box. 


Figure 140: Transom/keel knee


Gunwale knees are the next most complex piece. There are 2 bevels that need to be cut, and the order of cutting doesn't matter much. To do this you need to file away the outside corner of the knee so it clears the epoxy fillet. Next set it in place with the bottom of the knee on the sheer line and touching the transom in approximately the same spot that the bristol board pattern was sitting. Hold it carefully in place and slip a bevel gauge underneath to pick up the angle where the knee meets either the hull or the transom (hold the gauge perpendicular to the hull). Transfer that angle to the knee stock, and cut the first bevel. 

Figure 141: Transom/gunwale knee


Procedure for cutting bevels is the same as for scarphs. Plane to the line on one side, plane to the line on the other side (not necessary here since our "line" is really the top edge of the knee), mark the middle up with pencel and then plane away the ridge.  

Figure 142: Progress on cutting the bevel


After the first smash with the planer it's rare that it fits perfectly. The port knee required a few adjustments to get it sitting exactly at the angle I wanted and matched to the starboard side. Last thing was to cut the notch for the lap joint with the inner gunwale. 

Figure 143: Trying it for fit and making final adjustments


Figure 144: Finished knee with notch


The most complicated piece was the breasthook. To get the grain right I decided to cut it in 2 halves and glue it up. Some carefully-drilled alignment pins helped make sure I didn't have too bad of a ridge that would need to be planed/sanded away later. Ideally you would make the grain colours match a bit better than I did, but I don't care a whole lot. This piece was glued with the same WEST epoxy as the rest of the boat using the 404 adhesive filler. 

Figure 145: The breasthoook in two halves


Figure 146: Alignment pins


Figure 147: Final glue-up of breasthook


Cutting the bevels on the breasthook is a bit tricky, but not too bad. As before you need to lay the bottom edge up at the sheer line exactly where the bristol board pattern would sit. Pick up the angle for ALL THREE sides (in this case, the stem makes an angle as well), again holding the gauge perpendicular to the hull or stem as the case may be. Transfer angles to the breasthook and cut them. My skills must be getting better because this puppy fit on the first try!

Figure 148: Breasthook in place with bevels cut


Figure 149: Breasthook in place, from underneath


The breasthook will eventually receive notches for the inner gunwale just like the transom knees did. Now I have to decide how I'm going to attach it all -- glue up or screw it in place. 

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.