Cutting longish curve in plywood.

A good jig saw, with a sharp blade suitable for cutting plywood, would be my first choice for doing this.

You may find that a router will have a tendency to tearout most plywood ... ymmv.

With a jigsaw, go slow, take your time, cut just outside the line, use a wood rasp sander, to "fair the curve".

The more time and carefularity you take making the cut, the less cleanup/fairing you'll have to do.

... just my tuppence.

"WonderMonkey" wrote

usually do.

What is a fairing board?

A fairing board for this application will be a piece of 1/4-3/8 plywood about 3"W x 36LG with a handle at each end,

Use rubber cement and glue strips of 3"W, 24 grit sand paper to the plywood.

Stroke the fairing board across the curved jig saw cut line until smooth. (Change paper frequently).

A fairing batten for this job will be a 3/4"x3/4"x1/16"x96" aluminum angle.

Use back side of angle to check for high spots.

TIP: Rub the back side of the angle back and forth against the template surface. The aluminum will leave black marks on the high spots.

When your arms feel like they want to drop off, your template is fair.

When complete, you will have served your apprenticeship to fair out boat hulls.

Have fun.

Lew

You can forget about the template if...

1. You determine the radius of the arc you want to cut.
2. Take a 2-4" wide piece of ply a bit longer than the radius
3. Attach your jigsaw to the end of #2
4. Nail the other end of #2 to the ply you want to cut (one nail only) so distance bladenail equals desired radius. Enlarge the nail hole in #2 so it is the same diameter as the nail and so the nail will slip thru it easily.

Now you have a compass and can happily cut smoothly away :)

Works for Rugby balls (which, I think, have arcs of circles). American footballs (again, I surmise) have arc of an ellipse. For the latter, you'll need two nails.

Easiest way to get football shape is to layout a camber.

See Fred Bingham's book, Practical Yacht Joinery, for details.

Been there, done that.

Lew

And a string. I think you're correct, that an American football is an ellipse, but the one in the OP's photo has arcs that are so close to being circles as to not be noticeably different. Kerry

And he's gonna need a really strong needle to add the stiches.

Thanks for all the suggestions. I'll take them into consideration when I start on this project tonight.

Carefularity....excellent! ROY!

There are several ways to draw a curve, although I don't think that's your question. I probably would not make a template unless I would be making more than one item, but a template and router will work just fine. If the ply is thick, make more than one pass. If you are making just one football, draw, cut /w jigsaw (leaving the line), then sand to the line.

As others have said, a router will just make a mess of it. If you want to use a template, run the jigsaw along it.

Those look like circular arcs on that photo. It looks like the center point of each arc lies on the midpoint of the other arc.

And don't forget to put masking tape on area to be cut to prevent splintering along the cut edge if using plywood. W W