Posted by: Wayne | May 31, 2010

Bulkheads

Sorry, things have been busy and I haven’t posted in a bit.  I have gotten a wee bit done.  All of the remaining bulkheads were lofted onto a portion of a 4×8 sheet of plywood.  As noted previously, I had lofted the bulkheads onto butcher paper.  I then used the butcher paper patterns to optimize the layout on the plywood.  One of the bulkheads fit into an offcut, and the remaining pieces fit into an area roughly 2×5 feet.  I would use the paper patterns to locate where I wanted the piece, then I would draw my reference lines based on these, and re-loft onto the wood.  To get nice smooth curves I utilized two different sizes of drinking vessels.  The smaller one (~78mm) was used for the cutouts inside of bulkheads 6-8 (inside of the side seats).  The larger one (~116mm) was used for all of the curves on the inside of the upper pieces for bulkheads 3-8.

Lofting onto plywood. Procedure is basically the same as onto paper.

One of my highly scientific tools used to generate curves.

After this, I cut the end off of the sheet, then I cut it in half lengthwise.  I then screwed the two pieces together to ensure matching halves (and so I would only have to cut it out once).  At this point I used a ruler and a utility knife to score the cut lines (to reduce tear-out).

Scoring the cut lines to reduce tear-out.

Then it was time to cut out the pieces.  I ended up using two different blades on the jigsaw: a narrow one for the curved inner portions of the bulkheads and a wider one for the straight outer cuts.  Even swapping blades, they got more than a mite toasty and I let them and the jigsaw cool about every two pieces.  Eventually, all of the pieces were cut out.  Unfortunately, I managed to mis-cut the top portion of bulkhead 6, so I got to re-loft and re-cut that one.  Fortunately, it was a small piece.  I also cut out the transom (I had lofted it previously).

One of the many cuts needed to excise the bulkheads from the surrounding plywood.

So far, there have been a number of lessons learned.

  • Measure thrice, cut once (fortunately I only had to re-cut a small piece, not a big one).
  • Scoring the cut lines dramatically reduces tear-out.
  • Using a nice sharp blade also helps with tear-out.
  • Keeping the feed rate down with respect to the cyclic rate of the saw (smaller bites) helps with tear-out.
  • Cutting in the correct direction relative to the face grain reduces tear-out.  If the face grain is horizontal, and the piece you want is on the bottom, you want to cut downhill, not uphill.
  • Seeing pieces take shape is REALLY COOL!

As this post is getting a wee bit long, I will follow up later today with pictures of the assembled bulkheads and discussion on assembly.

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