Wednesday, December 17, 2008

Creating the Cap Rail

When we last met, I had finished making and gluing the plinth on to the pulpit. The next step is to cover the upper edges of the pulpit with the cap rail.

The cap rail is made up of 11 boards 3/4" thick by 2 3/4" wide. They get mitered where they meet at the corners. Since the corners in the center rear are cut off, they get mitered at that point as well. It gets even more complicated because the pulpit is made of 3 carcases that are bolted together. And there are handles, to boot!

The pieces that sit on top of the handles need to be wide enough that they cover the corner posts, but they also need to be narrow enough that a person can get their hands into the handles and hold on. This means that:

  • The pieces for the wing carcases need to be 2" wide at the rear, then narrow to the thickness of a 3/4" piece of plywood by the handle holes, then widen back to 2" near the point near the miter point.
  • The pieces for the center carcase need to be 1 3/4" wide at the rear, as that's the width of the rear post, then narrow to the thickness of a 3/4" piece of plywood by the handle holes, then widen back up to 1 3/4" near the miter point.
  • The pieces for the center carcase need to widen to 2 3/4" at the front in order to have the proper over hang that the rest of the parts have.

I had originally designed a complicated shape on the end of the front pieces for the wings where they meet the center pieces. They essentially needed to be mitered in two directions. That is, they needed to be mitered to go around the corner of the wing, and they needed to be mitered to meet the overhang on the center carcase. The picture below is a top view of the pulpit, generated by SketchUp, showing the pulpit as I had originally designed it, and it shows what I'm talking about.

The next picture, also from SketchUp, shows the shapes of the center carcase parts. One side is a mirror image of the other. The top piece in the picture is common to the wings. The pieces for the wings are similarly shaped, but wider because of the wider post. The other part is shorter & almost triangular in shape (see the picture above).

As always, I got started by cutting the stock to rough size, jointing, and planing it to thickness. I cut the pieces for everything except the parts that cover the ply partitions that meet 3" wide; I cut the other parts 4 1/2" wide. It was my intention to get the wing pieces & the center pieces from the wider boards.

I started by making the parts for the wings. I made the parts that go over the ends & the front first & mitered them. I used my Osbourne EB3 to cut the miters. I could have used my miter saw, but this worked just as well, and was more convenient, as my miter saw was in the shed.

At first, I decided to miter the front pieces for the wings in one direction only, instead of in two, and just let them meet the center carcase at a butt joint. The wings are only bolted to the center carcase, after all. So I cut the end of the front square & to length and then cut the miter for the mating part. And I made an error.

It turns out I cut this part 1/4" too short. I didn't have my drawing in front of me & I forgot that there is a 1/4" thick faux rail that overlaps the corner. Now I had to make up that 1/4", and I didn't want to just remake the part. I had extra stock, but I've gone through enough at this point, and I was trying to use parts that were cut consecutively from the same board. This makes the grain nearly continuous as it goes around the top.

So I ended up changing the shape of the part that covers the ply partition. I make it longer & added a tongue 1/4" wide that would make up for the missing 1/4" of length of the front piece. And I decided to go ahead & miter the front piece in both directions. This effectively shortened the length of this tongue.

To make this shape, I first added a tall auxiliary fence to my miter stock miter gauge. I then nibbled away about 3/8" to 1/2" of material near where the base of the tongue would meet the miter I needed to meet the front piece. I could then remove the rest of the material to form the tongue by making a stopped rip cut, and the material would fall away free.

I then set my table saw's blade bevel angle to 45° and made the miter cut. Next I returned the blade to 90° and cut the stock to width. This formed a piece from which I would get one half of the handle and the short piece that meets the front piece.

Next I took out my Osbourne EB3 & determined the miter angle that I needed to use to cut the miter piece from the handle piece. That turned out to be exactly 12°. I set the EB3 to that angle. I now determined where I needed to make the cut and carefully lined that point up with the blade. I cut the mitered piece free, and then I turned the remaining piece over (placing the face that had been toward the blade toward the miter gauge) and made the mating miter cut.

To keep everything balanced, I had to make both wings identically, so I repeated these steps for the other wing.

Next, I had to make the parts for the center section. I used a similar procedure, except that I attached the blanks to each other using double stick tape. I made sure the upper faced of both boards faced each other. This allowed me to make both parts for the center section at the same time, and each would be a perfect mirror of the other.

I had to make these parts twice. The first time through, I had made everything perfectly, but then I went & cut the miter for the front piece backwards. There was no way out of this mistake except to remake the parts, which I did. Also, I separated the two parts from each other before I cut the 12° miters, to make sure that the miters were in the right place!

At this point, I attached all of the parts that needed no further shaping to the wings. That is, the parts that all met at a 45° miter. I used glue & pocket hole screws to attach these parts to the carcases. Putting them on the carcase now would protect them from being dropped accidentally & getting banged up.

The next step was to produce two templates for the handle parts. To do this, I took two pieces of 3/4" ply scrap and cut them a little wider than the parts & a few inches longer. Next, I took some measurements from the pulpit & decided where I wanted the curves to be. I transferred the measurements to the ply & drove brads into the proper points.

Next, I took a piece of oak scrap & cut a strip about 1/16" thick from it. I threaded the strip through the brads and that was my curve. I traced the curve with a pencil onto the ply. Then I removed the brads and went to the band saw. After cutting the waste away, I took them to my drill press & installed my 2" drum (the biggest I have). I then sanded everything smooth & to the line.

After the templates were done, I was able to use them to cut the shape I needed out of the stock & pattern route the parts smooth. I then took out my 3/8" radius round over bit & rounded over the edges that needed it. I then did some sanding to blend everything together & make everything smooth.

It turns out, though, that I didn't make the dip I needed in these pieces deep enough -- they overhung the handles by about 1/4". So I took out my card scraper & removed the extra material. That was followed by some more sanding.

The last operation before I could attach these parts to the carcases was to cut the parts to length using a plumb cut. I used my bevel gauge to get this angle & transfer it to the miter gauge. And when that was done, I attached them to the carcases.

I put the carcases together & I then did even more sanding & some planing to get the parts smooth & aligned & level. I wanted everything to feel like one handle when the carcases are put together.

The following pictures show the finished cap rails. The first is a 3/4 view from the right front side.

Here's a shot showing the handles.

Looking down on the center section.

And another shot of the handles from the other side.

If you look closely in these pictures, you can see that I also made & installed the lectern support blocks with their shelf pin holes. The lectern will be hinged at the edge closest to the speaker. The shelf pins will then support the lectern & any notes the speaker has at the angle of their choosing. Or they can leave it flat & put a laptop computer on top,

We're getting very close to the end now. Next up, the maple trim goes on.

No comments: