: I drew the two joints on my CAD system and found some things to consider:
: First is the depth of the finished cove. When using 1/4 on 1/4 you get a
: pocket that is in theory 1/8" deep. If you use 3/8 on 1/4 the pocket
: ends up only 0.048" deep. The strips will have less "bite"
: with each other.
: Second is the "step" that will show up when you start to go around
: a curve. With 1/4 on 1/4 the joint acts like a hinge and the face stays
: tangent to the bead. With 3/8 on 1/4 the exposed bead is not tangent to
: the face and creates a "step". Laying strips on a form with a
: 6" radius would leave a .02" step (12.5 percent of the
: thickness) to be removed for a fair curve.
: Third, the same shift that causes a step on the outside leaves the same size
: hook on the inside.
: Fourth, The 3/8 on 1/4 joint has 30 pecent less surface area for glue.

: On the plus side, the 3/8 on 1/4" strips are about 12 percent wider.

Double check that drawing program -- and your calculator, too.

With 1/4 inch strips that have a full finished bead and cove with a 1/4 inch diameter you get a minimum of movement (geometrically there shouldn't be any) unless you remove some material from the coved edge on the inside of any bend. In practice you CAN rotate these joints, but they rotate like a lever around around a fulcrum which is the thin edge of the cove on the inside of and bend. Unless that fulcrum is removed, or distorted, the further you bend the joint the more the bead must pull out of the socket formed by the cove.

For that matter ANY size strips which have semicircular interlocking edges -- that is, where the diameter of the edge is the same as the thickness of the strip) should have this problem. The parts interlock so tightly that there is no room for play.

You don't have that problem with strips that are less than 1/4 inch thick. People working with 3/16th inch strips, or those who cut their strips to .250 inches and then planed them down to .245 inches (barely under 1/4 inch) get more freedom of movement.

With a larger diameter (or radius) for the edges of the strips you can move the joint further. The cove is no longer a semicircle, but a long arc which can ride along the arc of the bead, maintaining contact with it. As you move it, the inside may rise above the surface of the adjoining strip, and the outside will recede. This move of the strips away from a straight line should save a bit of sanding as it starts to form the curve you desire.

While the lip formed may be a few hundreths high (I'll take your figure of .02 inches on faith) it is not very wide, so it is removed fairly simply by sanding.

By the way, .02 is not 12.5% of the thickness of a 1/4 inch (.25) strip. It would be 2/25ths. Since 1/25th is 4 percent, then 2/25ths would be 8 percent. I think you reduced your fraction to 1/12.5, which would be numerically equivalent to 2/25, but would not express this fraction as a percentage. However, the value of this calculation is not particularly useful. Even correcting the size of the bump by reducing the amount from 12.5% to 8% does not make much sense. That .02 inch does not come off of the entire width of the strip, so we don't have to sand away 8% of the hull. (Thank Goodness!) We only have to remove a small corner of these strips, and that is a much smaller percentage still.

I'm curious, though, about how high the edge of two square-edged strips would be by comparison. I suspect it would be a bit higher. And this would have to be sanded down to create the smooth, fair, rounded surface on the outside of the hull. That might be an interesting drawing to try and measure.

PGJ