Home‎ > ‎

Day 1

05/01/2012

The first step in the building process for the Wood Duck is to assemble the puzzle joints.  Almost all plywood is sold in 8' long sheets.  Since the boat we want to build is longer than 8', we need a way to create parts that are longer.  One method would be to create scarf joints where two ends of plywood are planed to form mirror angles and then glued together with epoxy.  The CLC Chesapeake line of kayak kits as well as many others use the scarf joint method.  Scarf joints are actually stronger than the plywood alone, and they require no additional fiberglass  reinforcement.


On Wood Duck kits puzzle joints are used.  A puzzle joint is where two parts are precision cut on a CNC router to form interlocking fingers like jigsaw pieces. The puzzle pieces are then joined with epoxy and reinforced with fiberglass.

Step one in assembling the Wood Duck puzzle joints is to lay out all of the parts on a sheet of plastic.  The purpose here is to make sure that you are selecting the most attractive sides of the plywood to make up the outside of the boat (those sides are facing down) and to make sure you are making left and right sides of the boat.  Having two left sheer panels would not work out very well in the final assembly.  


The puzzle fingers are precision cut at the factory and they fit together very tightly.  The manual says to place a block of wood over the joint and gently tap the pieces into place, but I have seen plywood veneer separate when it is forced so I would rather avoid that.  Instead of forcing them I lightly ran a steel rasp around each joint to ensure the pieces would go together smoothly while still achieving a tight fit.  

There was a large mill sticker on one of my bottom panels at the puzzle joint.  The manual says these can be removed by sanding, but I found removing all of the adhesive nearly impossible even with 80 grit sand paper.  If the adhesive is not removed then the epoxy will not soak into the wood resulting in a weak joint.  I used a razor blade to gently scrape off the adhesive, then sanded, then more scraping, then more sanding and so on until all traces of the sticker were gone.

Once all of the parts were laid out correctly with the ugly side up it's time to mix up epoxy.  Having never worked with epoxy or fiberglass before, this is where I started to get a little nervous.  That is not a bad thing, because it made me take my time and read everything twice to make sure I was doing it right.  The manual says the epoxy should be mixed at a 2:1 ratio, resin to thickener.  The pumps that come with the kit are calibrated to provide this ratio with a single stroke on each, you just have to be sure to get the right pump in the right container.  The epoxy for this step is mixed, thickened with silica powder to a mustard like consistency (whatever that means), and then brushed onto the joints.  The joints are assembled and painted with more epoxy and then overlaid with a strip of fiberglass tape which is then saturated with more epoxy.


In my research on working with epoxy, I came upon numerous warnings about over-saturating the glass.  Over-saturating can cause the fiberglass weave to "float" on the wood which prevents good adhesion.  Of course you are also warned not to starve the wood by not applying enough epoxy because the dry wood absorbs it.  The question no one seems to answer clearly is how much is too much, and how much is not enough.  I ended up applying the epoxy with a disposable brush and then smoothing it out with my fingers (wearing nitrile gloves of course).  Any thick spots I gently squeegeed the excess to the edges of the glass tape, and for any light spots I brushed on a little more epoxy.  This method seemed to work pretty well.

The final part of tonight's work is to make sure that the panels are flush with their adjoining pieces.  Once the epoxy cures the only way to correct any misalignment will be to use a plane or sanding paper to shave off the uneven edges which would be ugly and not as strong.  I lined up all of the joints and spread a strip of plastic over them, laid down some scrap 2x4's so the taped joints were covered, and then weighted those down with anything heavy I could find.  That should be enough downward pressure to align the joints and make the tape cure completely flat.  The epoxy needs to cure overnight, so we'll see how it looks tomorrow night.




Total time on this phase: 1.5 hrs. 
Total time on construction: 1.5 hours
Comments