Monday, December 8, 2008

Here a Plinth, There a Plinth . . .

Time for another update on the pulpit. I'm getting near to the end of it now!

Just to remind you where the pulpit project stands so far: I've got the three carcases put together. I've modified the carcases by cutting off the rear corners on the 4 ply partitions. I've made a design change to add handles at my pastor's request. I've actually made & installed the handles into the ply partitions. The next task to tackle is to make the plinth that goes all the way around the bottom of the pulpit.

For those of you who don't know what a "plinth" is, it's the sub-base that goes all the way around the bottom of the pulpit. It's made of thick boards that are mitered at the outside corners. An ogee trim molding will wrap the bottom, hiding the joints between the plinth & the carcases.

The stock for the plinth I had was 6/4 by 9" x 48". It needed to be thicknessed to 1 5/16" thick. And, of course, I needed to rip the three boards in half before I could joint them. The stock had a few ugly black knots on a couple of the boards, and one board had some perfectly round holes about 1/16" in diameter. These looked like bug holes. The holes weren't growing & there was no dust near the board, so I'm pretty sure the critters were dead. I've never had any wood with such bug tracks in it before, so this was a bit different for me.

After ripping, jointing, and thicknessing, I ripped everything to 4 1/4". The final width needed to be 4", but I wanted to leave some room for adjusting the alignment of the grain, if needed. Next, I cut a 3/4" wide by 3/8" deep rabbet along one edge of each board. The way the pulpit is designed, this rabbet matches up with the 3/8" rabbet I cut on the bottom of the corner posts. The rabbet also give me more gluing surface.

After cutting the rabbet, I had to figure out how to cut up the boards to get the parts I needed. I went back to my SketchUp drawing & took the dimensions from it. Then I imported these into CutList Plus & had it generate the layouts. Then I began to cut the stock.

Because the corners were all mitered, I figured I'd use my 10" chop saw to get good 45° cuts. So I went out & I bought a new 10" thin kerf cross cut blade to use on the chop saw. I mounted the blade & ripped a ply scrap about 36" long to 4 1/2" wide. I intended to use this scrap as an auxiliary fence to back up the cuts on the miter saw & reduce tear out. Then I mounted the auxiliary fence to the saw.

That's when I found that my chop saw doesn't have the capacity to cut through anything that tall. So I tried ripping 1/2" off of the auxiliary fence. The saw cut through the aux fence, so I marked where I wanted to make my first cut on my stock. I put the stock in the saw & lined up my marks. And that's when I found that my saw can't cut all the way through 4 1/4" wide stock, either.

So I removed the new blade from the chop saw, put the chop saw away, and mounted the new blade on my table saw. I then titled the blade to 45°. Some test cuts confirmed the blade was at a true 45°. And I started cutting.

Rather than trust the dimensions on the plan, I tried to determine the length by placing the stock against the place it had to go & marking it. This worked great, yet somehow I managed to screw up one piece in the back of the pulpit. I cut it too short.

The pieces on the back of the wings have one mitered corner & one cut at 90°. The piece in the back on the center section has two 90° corners. When I cut the piece for one of the wings, I measured it. And it came out 5/8" too short.

I didn't discover the problem until after I'd cut the rest of the parts. I just didn't have the stock to remake the part. And given that I am no longer gainfully employed, I didn't have the cash to go out & buy a new piece of stock.

So I tried cutting a miter on the short end & cutting a miter on a piece whose grain matched very closely, in order to make a ship lap joint. I used 5 minute epoxy to glue the two parts together. The end result is a very good match, so the joint should be easy to hide when I get to the finishing steps.

After getting all of the parts to rough length, I then spent about a week or so just trying to get all of the outside mitered corners to meet properly and the parts cut to proper length. It turns out that the corners of some of the posts weren't perfectly square. So even though everything is parallel, I had to carefully remove material, and in some cases add it, in order to get the corners to fit properly.

Once the parts all fit together properly, I had to shape the feet on the plinth. This took a couple of days to complete, given the number of parts. I made a template out of 1/2" MDF and used it to trace the shape on to each board in the proper places, namely, at the mitered corners. Time to cut the shape.

I used a 1" Forstner bit to drill out the arc in the corner where the foot transitions into the bottom, then I used my table saw or band saw to remove the waste material. I used the table saw for those parts that had a foot on one end, and the band saw for those that had feet at both ends. I used a 1" chisel to clean up the transition on those parts that I used the table saw to remove the waste.

After sanding everything, I finally started gluing the parts on to the pulpit. I used glue & clamps only, working with one piece at a time. I'd let it sit for 30 minutes or so before I started on the next piece.

Here are some shots of the pulpit & completed plinth. First, the whole pulpit from the front:

The right wing end:

A close up of the center front:

That's enough for now. Next time, we'll go over the cap rails, which I should finish up today.

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