Starting the Project

Posted on May 13, 2021 by Theodric

So I decided I wanted to build a lighthouse. After some thought, it occurred to me that since I always enjoy visiting Provincetown, whether by land or by sea, building one of the lighthouses in Provincetown would be a fun project.

There are three lighthouses in Provincetown, Race Point Light, Wood End Light, and Long Point Light.

  • Race Point Light
  • Wood End Light
  • Long Point Light

The locations of these three lights can be seen on the nautical chart below. A lighthouse (or other lighted navigational aid) is indicated by a black dot and a purple teardrop shape (light symbol). Race Point Light is at the upper left of the picture (flashes white once every 10 seconds). Wood End Light is at the bottom of the picture (flashes red once every 10 seconds). And Long Point Light is to the right of Wood End (it has green light that occults (turns off) once every 4 seconds).

Nautical Chart of Provincetown Harbor

Race Point Light is round, and I wasn’t quite sure how to construct that. Wood End and Long Point lights are almost identical, so I picked Wood End, which is also a bit easier to get to by foot.

The first step in the project was drawing up plans. This required knowing the dimensions of the actual lighthouse. There is a dyke (erroneously called “The Jetty” by some of the locals) that leads from the Provincetown Inn out to Wood End. If the tide is low enough, you can walk all the way out there. In September 2019, I went out there with a tape measure and a camera, and took a bunch of pictures and measurements.

  • Northwest Corner
  • West Side
  • South Side
  • East Side
Click pictures above to enlarge

And, of course I took a selfie…

  • Wood End Light Selfie

Based on the photos and my measurements, I estimate that the lighthouse is 41 feet high, including the lightning rod at the top of the finial. I opted for a 1:12 scale model, so that will make my model 3 feet, 5 inches tall.

I will put some plans and pictures below. Over the next few months, I’ll continue to add updates, as well as explanations of many of the pictures.

  • 1:4 Scale Drawing of North side of Lighthouse

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Making the Roof

Posted on May 18, 2021 by Theodric

Somewhere I got the idea that I should make the roof of the lighthouse out of bent sheet metal. I made the drawing below based on photographs and measurements of the actual lighthouse, and from there determined the rest of the angles and dimensions of the roof. Note that the dimensions of the roof shown below are along the vertices of the roof panels.

Lighthouse Cupola Plans

One of the first thing to notice about the top of the lighthouse is that it’s a decagon (10 sides). So the roof consists of 10 flat trapezoidal panels, each at an specific angle to each other and each at a specific angle to the horizon.

Roof Dimensions #1

To determine the dimensions, I calculated the sizes of 10 triangular panels, arranged in a decagon, each sloped to come to a point 2.832″ above the base level. Each triangle would have sides of 4.799″ and a base of 2.395″. Each triangle should be sloped up at 37.5°. This gave me the sizes of the trapezoids that would need to be cut out of the sheet metal.

Roof Dimensions #2

Below is an SVG file with the correct dimensions that I created with a short C program. I printed this out on paper, and then put it together with scissors and tape to verify that it would create the correct size and shape of the roof.

  • SVG File: Scale Drawing of Roof Layout

The printout of the above SVG file was then used to transfer the pattern to 22 gauge (0.025″ thick) aluminum sheet metal.

I would need a way to bend each vertex to the correct angle, so I constructed a sheet metal bending tool that would do just that. (Note that for some reason, I originally calculated this angle to be 17°, but as you can see in the Roof Dimensions #1 drawing above, this angle should really be about 21.5°. But it didn’t seem to matter in the long run.) The drawings for the bending tool are shown below.

Dimensions of Roof Panel and Roof Bending Tool
Dimensions of Roof Bending Tool

Below are pictures of the actual bending tool, made out of aluminum and created on a Bridgeport mill.

Aluminum Roof Bending Tool

The tool works by lining up the vertex between each roof panel in the holes drilled along the center of the bender. Then the two pieces are squeezed together with a nut and bolt at either end. When the nuts are tightened on each side, the V-shape of the tool bends the sheet metal to the correct angle. Here are pics of the roof bending tool being used to create the actual roof.

  • Top view of the roof being bent to the correct shape
  • Bottom view of the roof being bent to the correct shape
  • Top view of the roof after being bent

Note that tabs were left at the bottom of each panel. These tabs were bent in with a commercial sheet bending tool that had been cut down to the correct size (see below).

  • Commercial Sheet Metal Bender
  • Bottom View of Roof
  • Roof with Bottom Tabs Bent In

Finally, a center piece of 1/2″ aluminum was milled into a shape with 10 sides, each sloping down at 37.5°. Then pop rivets were used to attach the top of each roof panel to this center piece. The center hole of this piece would be used to attach the finial. Note that the other 10 holes just made it easier to clamp down the piece when it was being milled.

  • Completed Roof

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