Cutting a Rabbet Line

When building a ship model that will have its hull planked, you’ve got to cut a rabbet.  I didn’t need to do this on my solid hull model (no planking), so when I hit this step on my plank-on-bulkhead build, it was my first time.

I stalled for days.  After building the center keel, the last thing I wanted to do was to start hacking away at it.  I searched for information online, and found very little.

Photo Apr 07, 6 24 30 PM
The rabbet on my Bluenose, about halfway done.

Most discussion of the actual procedure was basically ‘carve it down’.  There was a lot of info about what a bearding line and rabbet line are, but very little about how to actually cut it.

I suspect there’s little info because once you’ve done it, you realize it isn’t a big deal.  It is easy and doesn’t take long.  So, after your first one, it is just a minor step.  However, when you’re starting out, it can be daunting.

Here’s how I did it.

Quick Introduction

Hull planking runs down the hull of the ship.  Where it hits the bottom keel, it needs to ‘slot’ into a groove so the planking lays flush with the keel.  This creates a joint that would seal against water coming in.  (Over simplified explanation.)

The rabbet cut is made with two lines.  The first is the bearding line.  This is higher up the center keel, and represents the top edge of the cut.

The second is the rabbet line, which is the bottom edge of the cut.  You’ll be carving down from the bearding line to the rabbet line.  Both of these lines are typically marked on the plans.  (Forgive my crude drawing.  I don’t “art well”.)

rabbet
Why is the rabbet cut necessary?

Planks sit at an angle in the rabbet cut.  Since planks are rectangular, they have a back corner that goes into this groove.  So really, you want that bottom edge to be angled to match how the plank will lay.

So, we need a cut that looks like this…

rabbet2

It is important to note that every ship has a different shape, and that shape changes along the length of the ship.  This means that the planks will lay differently at different parts of the ship.  This is why your bearding line and rabbet lines may curve, becoming closer together or farther apart.  Regardless of the distance between the two lines, the idea is exactly the same – it is a ‘v’ cut from the bearding line to the rabbet line.  If the lines are father apart, it just means the angle will be less severe.

How I Cut the Rabbet

Start by transferring the bearding and rabbet lines from the plans.  You can do this by cutting out the plans along those lines and tracing, using the edge of the paper as your guide (you might want to copy your plans if you do this).

I tried that, and wasn’t confident my lines were accurate.  So, I did this:

  1. Using a straight edge, I drew lines down the keel where each bulkhead will sit.
  2. Using dividers, I measured the distance from the top of each bulkhead down to the bearding line.  I marked this on the keel with a dot on each bulkhead line.  I checked my work by also measuring the distance up from the bottom of the keel to each mark.  Do this on both sides of the keel.
  3. I repeated the process for the rabbet line.  This time measuring down from the bearding line mark to the rabbet line, and up from the bottom of the keel to the rabbet line.  Marks were made on both sides.
  4. This gives me a series of marks that show where the line should go.  I then used my cut out plans, aligned to these lines, to draw the curves.
Photo Apr 05, 7 55 24 PM
Start by marking the exact positions of the bearding line (curved) and rabbet line (straight, at the bottom).  These are always marked on the plans.

This method removes an variance caused by the shape of the overall center keel.  I knew that I had the right distance from the top and bottom, and knew that my line was traced accurately if it hit all the marks.  Some were a little off – I deferred to the cut plans when things didn’t line up exactly.

Now you’ve got to start cutting.

  1. Score both the rabbet line and bearding line with a #11 blade.  I started between the middle bulkheads, where the cut was narrow, and I did one  bulkhead-space at a time.

    Photo Apr 10, 8 11 45 AM
    I start by scoring the lines.
  2. Take my chisel x-acto blade, and push it into the score on the rabbet line, matching the angle for the bottom of the plank.  I cut a small (1″ long) piece of plank to help with the process.  This gives me a lower ‘lip’ on the rabbet at the right angle for the plank.  Repeat this for the length of the section.  How deep do you go?  Depends on the thickness of your planks.  Start shallow and go deeper after you’ve tested some.  For my particular situation, I needed to push the chisel in until the bevel at the tip was all the way in.  (I needed about 1/16″ in my case.)

    Photo Apr 10, 8 12 52 AM
    Next I use a chisel blade to cut to the right depth along the rabbet line.
  3. Take my chisel and carve down from the bearding line to the rabbet line, where I hit the deeper cut I previously made.  Big chunk of wood comes out.

    Photo Apr 07, 6 19 20 PM
    Then I use the chisel to shave off wood from the bearding line to the rabbet line.
  4. After I’ve ‘roughed out’ the section, drop the test plank in and slide it along the cut.  It should sit at the appropriate angle against the hull, and anywhere that it doesn’t seam up with the rabbet line just right gets some touch-up work.

    Photo Apr 10, 8 15 40 AM
    I work in sections (between bulkheads), and use a scrap piece of planking wood to test the cut’s fit.
  5. Repeat for every section, on both sides.  Sand when done.

You want a nice, smooth bevel down from the bearding line to the rabbet line.  I found the narrow areas (where the lines were closer) to be easier than the larger sections in the rear.

Constantly slide your test plank along the cut, and remove any excess material when it sits too high.

Sand everything when you’re finished.  I started with 100 grit paper, and worked my way up to 400 grit.

Cutting and sanding took an hour or so.  Drawing the lines took about half an hour.  Later in the build process I had to fine-tune some spots, especially in the larger areas of the cut at the stern, but that was a 5-minute project.

As always, an experienced modeler may tell you this method is completely wrong.  I’m not suggesting this the “correct” way to do it…it is just how I did it.