Demilune Table, Part 2: Experimentation

Warning: this one runs a bit long, but it's mostly pics ...

This project has been an exercise in experimentation.  For a couple different reasons, I didn't want to make a three inch wide bent lamination that would be about 36-38" along the curve.

First experiment: making the curved apron in pieces, shown here in pictures.  The plan is to make three separate curved apron pieces that will join to the legs with m&t joints.

The working drawing

On a poplar blank, drew a 10 7/8" radius

Some of the tools used to remove material and smooth the curve (rip saw not shown)

Cut and planed a 1/8" slice from a piece of cherry

Testing to see if it will bend to the 10 7/8" radius - it won't

Thinning the cherry down to 1/16"

Gluing it to the poplar curved piece

This worked well, albeit with a few small gaps

The bigger issue here is grain direction.  At the ends of this piece, the cherry is glued to end grain more than long grain.  I used PVA glue.  Time will tell if this holds.

Second experiment: mortise and tenon joint that will join the apron and leg.  In the picture below, I've placed the middle front apron in position on the drawing and you can see the outline of the leg.

The pencil lines on the poplar are parallel to the front face of the leg.  That's the direction
the tenon would be cut if a mortise was chopped perpendicular into the leg's side face.  This
does not utilize the long grain strength of the apron.

If the tenon was cut in line with the grain of the poplar, the mortise would have a very steep angle.  This is not necessarily a terrible thing, just a pain to lay out and execute properly.  I decided on a compromise and used an angle in between the two.

The compromise angle

I made a small template with the mortise layout and traced it onto the top of the leg.
Those lines helped me cut the angle.  The joint is being tested here in a scrap leg blank

There are issues with this.  But it's a compromise and this table probably won't be seeing any/much abuse - at least not while we own it.

Here's the next issue: there needs to be another mortise on the other side of that leg and there's not a lot of space to put it.  I've thought about staggering the two mortises.  The mortise on left would be full depth for its upper half and just 1/2" deep at bottom.  The mortise on the right would be just the opposite.

Layout of the left front leg mortises

Transferring the lines to a test piece

The test leg with mortises cut: on the right side, the top is full depth (about 1 1/8")
and bottom is about 5/8" deep.  The left side mortise is full depth at the bottom.

The middle apron piece with tenon cut

Left front leg (practice piece) with two apron pieces fitted in their mortises

A nice friction fit

This seems to have worked out OK, but there are a couple of problems with it.  First, small errors in layout or execution of the joints resulted in the apron not following the curve quite right - The combined curve of these two apron pieces is tighter (smaller radius, that is) than it should be.

The second problem is something that really bothers me: I'm not sure about the ultimate sturdiness of the table with this configuration.  Unlike a table with 90° joints holding the piece together, you can't really clamp this undercarriage together tightly without stressing some of the joints or pulling the whole thing out of its semi-round shape.

It got me thinking about alternate ways to make a single piece apron.  I woke up the other morning with a possible solution in my head.  I'd try to glue up several pieces and then shape them to the half round, like in the pictures below, then glue a 1/16" piece of cherry to it.

Bunch of pieces glued together

Then shaped to the half round (not yet smoothed in this pic)

However, it just seemed futile for strength reasons.  In the end, I might have to bite the bullet and make a half round form and glue-laminate a bunch of 1/16" slices of 3" wide wood together.  That's at least 12 slices of 1/16" x 3" x 36"!!  Not my idea of fun.  But hay, if I had just done this from the start, it would have been over a long time ago.

Back to the experiments.  The third experiment had to do with a decorative bead at the bottom of the aprons that is proud of the apron's surface.  The plan is to glue a piece to the underside of the apron.  I put a piece of 1/4" thick scrap under an apron piece and used a divider set at 1/8" to scribe an arc, referencing off the apron.  Then I cut to that line and smoothed a 1/8" radius along that edge.

The test piece with curve cut

1/8" radius along the front edge

There's the test piece sitting below the apron.  It's not the right length,
but it gives the idea and I think it will look good.

Enough for now.  Time to make some decisions about how to proceed.