Router Gauge

 This weekend's scarfing showed me the need for an easier way to adjust the router's bit-depth.  

Using some scrap of red oak planking I made a stout little block.  Good weight for a little block and perfectly flat bottom.

Then I found a really old tape measure that had a millimeters scale on it.  Carefully cut it and taped it to the block using some two-sided carpet tape.  I covered the rest of the carpet tape over with duct tape.

gauge block

21.2 mm

Scarfing Begins

In the 'stitch and glue' method of building the hull, the bottom and sides must be single pieces.  On a 18'-6" boat this means the bottom and sides are far larger than a standard 4x8 foot sheet of plywood.  Scarfing is the technique of joining sheets of plywood together to make really big pieces of plywood.

After a couple of weeks of testing both 'stepped scarfing' and the traditional 'tapered scarfing', I chose traditional tapering.  It has two advantages; setting router bit height is easier than the stepped scarfing method, and the flat taper is far easier to spread epoxy glue on.

There are numerous ways of cutting the taper.  Since I already owned a good router I chose this method and made a jig to router the taper at a consistent angle.  Searching the internet shows many jigs for router scarfing but most are for narrow boards.  I need to scarf the entire 8 foot length of my plywood and pondered some days away to design this carriage sliding along a groove in a straight edge.

 This jig is specific to 12mm plywood, cut to a 3 inch wide taper.  The angle the router runs up and down at is determined by the height of the carriage runners.  The bottom runner slides directly on the table and the upper runner slides in a channel on the straight edge.  

I did a test on some scrape plywood in my basement shop. This gave me an important piece of knowledge.  With this jig setup and method it is very important that the table, plywood, and straight-edge guide be at precise heights.  I accomplished this by screwing the two sheets of plywood to the table every 16 inches and screwing down the guide every 8 inches, holding the whole works tightly together.  Yes, this puts many screw holes in my boat, but putty and paint cures many things.

Side notes; Carriage and straight-edge guide are made from an old piece of pergo flooring.  To prevent the carriage from bending to the weight of the router I nailed and glued two short walls on either side just under the router handles.  Also, I placed the bottom stop precisely to prevent the router from cutting into the table, which in my case is other pieces of plywood stacked up.

Cutting is done in three stages.  The first two takes off about 5mm each stage, then the third time the router bit-depth is carefully adjusted to do the final cut.  Even with the vacuum attached to the router, I had to stop a half dozen times to vacuum away the piles of sawdust.

The first 4 feet cut.  The guide is then moved to the remaining 4 feet.  The plywood remains screwed in place. 

First 4 feet of the 8 foot length.

 The finished cut, unscrewed from the table and separated.

The finished cut.

 There are 12 scarf joints to be done before the bottom and side panels can be cut out.  There are four 8-foot scarfs, and eight 4-foot scarfs.  A total of 64 feet of scarfing to do.  I managed to get two 8-foot scarfs cut on Saturday and two more on Sunday, that's 4 of 12 scarfs and half the total distance.  

Today I rest.

 

Progress again. Second coat of Epoxy.

 April was a busy time at work but I'm now into my part-time phase of retiring so I've managed to find a little time to continue on the boat.

I've managed to get two coats of epoxy on the frames and bulkheads.  I feel this is enough to seal the wood, which is the primary goal at this point.  After the hull is assembled the plywood will receive several coats of either paint or varnish (varnished 'bright-work' will be mostly inside the cabin only). 

all shiny now.

 The first coat of epoxy was to 'wet' the plywood and so was spread fairly thin using a plastic squeegee and then rolled with a foam roller.  Like any first-coat, this raised the fibers of the wood and received some sanding before the second coat.

I wanted the second coat to have some thickness and I sought a way of distributing an even amount of epoxy across the plywood.  At first I tried a notched trowel, but found the thin and runny (low viscosity) epoxy just flowed through without really spreading.  Then I tried my plastic squeegee but couldn't regulate all the areas to have roughly the same amount of epoxy.  

4-1/2 inch mixing bowl, 3/4 inch wide mixing stick, and 4 inch foam roller 

 I ended up with a technique of making a batch of epoxy (estimating how much to make up).  Then I used my mixing stick to spoon it out of the bowl and drizzle it around the entire piece until the bowl was empty and the drizzled epoxy looked roughly distributed evenly.  (Oh, the binder clip on the mixing cup??  That's a reminder to always pick it up from the same side, so I don't get the epoxy all over my clean gloves.)

Next step was to roll the drizzles flat to spread them out.  If my roller was new, I made one area of drizzles extra thick and started my roller there so that the amount of epoxy used to wet out the roller did not leave the starting area too thin.  Roll with long strokes and keep away from the edges at this point, you don't want a thick drizzle splotch pushed over the edge.  (I can't recommend having palsy in your old-age, but the shaky hands do, in fact, make drizzling back and forth effortless.)

After the initial roll out, I worked the edges.  Using shorter strokes and the roller at an angle to the edge.  The angle allows me to roll most of roller past the edge without actually dropping over or off the edge. 

After all the edges are coated, I finished by rolling the entire area first one direction then the other.  This gave what at least appeared to be a fairly even and uniform thickness of epoxy across the whole works.

Using a slow version of epoxy hardener, allowed the epoxy to still be fairly wet after the rolling.  This allowed time for the low-viscosity epoxy to spread and level itself resulting in a somewhat smooth surface without roller marks or impressions.

I did not do the 'tipping' the books talk about.  Tipping is following the roller work with a gentle one direction brushing to help smooth things, pop air bubbles, etc.