June 8, 2011

Canoe Mold Build Day 7

Foam shaped from side

Foam shaped from side

Day 7 was all about the shaping of the foam. Tony quickly stepped into the role of master shaper while Kevin worked on rough shaping and I did foam strengthening. By the end of day 7 we had completed the shaping and sanded the surface of the foam smooth.

Shaping

Tony shaping foam

Tony shaping foam

Kevin shaping foam

Kevin shaping foam

In the day 6 post I mentioned that a rasp was an essential tool for shaping the canoe according to our testing. In day 7 as we went about shaping the canoe we realized the rasp was AMAZING for achieving a uniform and desired shape. While the dual action sander was great for smoothing the rough surface the rasp left behind, it was poor tool choice for shaping the foam. The sander with an aggressive 60 or 80 grit had a tendency to dig into the surface too much on account of the 5″ disc of the abrasive areas. The rasp was about 2″ wide making it just a bit wider than the foam strips. This 2″ of width was combined with a diagonal stroke across the mold a very uniform and consistent cut across the foam was delivered. Kudos to Tony for discovering this technique. The only major challenge we had with the rasp, and the sander, was the foam vibrating or bowing in when running the tools over it.

Strengthening

Foam reinforcement

Foam reinforcement

To overcome the challenge of the foam strips flexing when rasping and sanding I embarked on a mission to strengthen the foam strips from within the mold. To strengthen the foam I added strips inside the mold in between the strongbacks that went laterally across the foam strips. I used scrap pieces of foam from the initial foaming of the strongback. I broke pieces ranging from 3″ to 6″ depending on the curve of the area and then I laid a nice 1/4″ bead of hot glue across the piece. Once the glue was in place I would position the piece and hold it there until the glue setup. It was a slow process that was hard on the back due to being in a laying position on the ground. While the process was slow (I actually did this over the next 4 days before the official day 8 meet of Kevin, Tony, and I)  it did yield great results. The strength across the mold was MUCH stronger and allowed for much faster shaping. Moran mentioned that 5/8″ plywood for the strongback offered more glueing surface for the foam that resulted in greater strength, although we used 1/” plywood. After going through this strengthening process I would recommend using 5/8″ plywood for additional foam strength. If I build a second mold I will be using the 5/8″ thick plywood.

Sanding

Once the right lines and curves of the canoe are achieved with the rasp it was time to use a dual action sander with 80 grit sand paper to get the smooth surface that we need for mudding the canoe. The sanding process did not take that long since it was just a smoothing and not a shaping operation. It was helpful as the canoe achieved a smoother surface as we did find areas that needed more shaping to achieve the desired curve or line. As with each step of this process just take your time and be patient. While for most parts of the build the next step offers you the ability to correct issues with the previous step, it is best to avoid having to fix these issues later. Care now will save time later.

Bow & Stern Trimming

Foam shaped from top

Foam shaped from top

Trimming of the bow and stern seemed daunting as mistakes here lead to time consuming foam repairs, but it was fairly simple. Just take your time and be gentle. We used a flat hand saw with a flexible blade. We ran the blade down each side of the bow/stern while flexing the blade to match the contour of the surface leading up to the bow/stern. After we ran a cut down both sides on the bow/stern we had a very nice edge. While the foam did have some gaps in it due to placement of the foam it was no big deal as we were able to glue chunks of foam in to help fill those spaces. Remember Moran did mention that you can have up to 1/2″ gaps in the foam as the drywall can fill it. However, I would not recommend exceeding a 1/4″ gap between the foam. The mud in the 1/2″ gaps takes too long to dry and is quite brittle. It is a better use of your time to glue in some small chunks of foam.

In ensuring that the bow/stern were true we did use the measurements from the bow/stern sketches to help validate that are work truing the mold player through into having a true bow/stern. As we were shaping and sanding the bow/stern they seemed to look crooked or off, but by the measurements and plumb they were correct.

Key Learnings

  • Rasps are great for shaping. Be sure to use a diagonal pattern as you run the rasp across the canoe.
  • Adding additional support inside the canoe to run across the 1 5/8″ strips of foam will greatly increase the effectiveness of using the rasp and shaping consistently
  • A dual action sander with 80 grit paper is the way to smooth out the rough surface left behind from the rasp.
  • The shaping process takes much longer that you would think.
  • Using measurement from the bow and stern sketches is helpful for accurate shaping.
  • Avoid gaps larger than 1/4″ in the foam. Moran says 1/2″ but it takes too long to dry and ends up being too brittle.
~Nathan

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