Notching plywood

[potomac]

A couple recent threads (John How's Fulmar build and one regarding some new Lee Valley chisels) have put me in mind of a question. When notching plywood to accept stringers or ribbands, what method do forum members use to make the square cut parallel to the outside of the mold or frame. The two perpendicular cuts are easily accomplished with a jigsaw or even a skilsaw. I have either drilled holes inside the cutout, then come back with a coping saw to complete the parallel cut, or brought the jigsaw in a curve to remove most of the notch waste and then cleaned up with a coping saw. Is there a better or easier method?

On solid wood, this would be achieved with good chisels which is why the other threads put me in mind of this question.

Thanks- Aaron

[Paul Pless]

Hard to think of a more accurate or efficient method than using a router.

[David G]

I typically put a dado head in the table saw and cut each notch in one or two passes.

[wizbang 13]

Generally, have no need for precision, cuz of epoxy.
If a cut were too accurate , I would mutila.., um, open it a bit to make room for the dukee.

[TerryLL]

Hard to beat the coping saw for accuracy and simplicity, especially if the frames (or molds) are already mounted on the building frame.

[David G]

Hard to beat the coping saw for accuracy and simplicity, especially if the frames (or molds) are already mounted on the building frame.

Jigsaw if it'll fit.

If not... backsaw to depth and coping saw across the bottom. Tedious.

[John How]

I'm not sure what part you are notching. I used ribands on the molds of my Fulmar, they are not part of the boat though and I just made the molds smaller by the thickness of the riband so there are no notches, is that what you mean? I needed to be able to adjust the ribands for fairness and that is why I did it that way. On the stern, I made small blocks to hold the end of the riband and at the bow, they will float and will be clamped to the edge of each new plank but not glued.
An advantage of this method is that the mold need not have flats on it where the planks lay except at the transom.

[potomac]

John- Sort of a stream of consciousness thing, but in essence, your build put me in mind of Tom Hill's method of lining off strakes, which reminded me of an idea I had utilizing plans designed for thin planking stock without much internal framing(like your Fulmar) where the molds would become the outline for the internal plywood framing for a skin on frame version. I am working on this idea with some Joel White designs. I have also seen it done with Michalak's LFH 17. The above described framing is akin to the type of framing you see in Dave Gentry's original designs or in Tom Yost's. I am hoping to use this same idea with sailing vessels. The problem with sailing vessels is the risk becomes slightly greater than with rowing/ paddling craft because of all the necessary rigging, sails, foils, etc.. So in my case, it has to be a design you'd like to build in wood as well should the SOF thing not work out as hoped. I'm starting small and we'll see how it goes from there.

I am actually working on a Dave Gentry design right now and while I have utilized the coping saw method, thought maybe there was a far and away better method

[keyhavenpotterer]

Gemoterically taking off 20mm say for a 20mm stringer won't give you the hull shape you started with. The stringers come accross the mold edge at an angle, not perpendicular to the mold towards the stems, so the lateral width of the stringer at that point may be 23-24mm, so the molds would have to be cut down by that amount to be fair or how it was drawn. You could achieve it with a bevel board. Without cutting off the extra, you risk a hard spot or a boat with greater beam than it was supposed to have. Tom Hill's reccomendation in his book (a great book) is geometrically imperfect. None of this matters much of course.

Flush cut laminate trimmer using a pattern clamped under the mold. Leave the round edges on the corners of the notch. Round over the internal edges of the stringer with the same radius as the router bit. Fits perfect, holds paint, no internal hard edges in the boat (if they're staying in) or splinters and bends nice.

Ed

[hokiefan]

A couple recent threads (John How's Fulmar build and one regarding some new Lee Valley chisels) have put me in mind of a question. When notching plywood to accept stringers or ribbands, what method do forum members use to make the square cut parallel to the outside of the mold or frame. The two perpendicular cuts are easily accomplished with a jigsaw or even a skilsaw. I have either drilled holes inside the cutout, then come back with a coping saw to complete the parallel cut, or brought the jigsaw in a curve to remove most of the notch waste and then cleaned up with a coping saw. Is there a better or easier method?

On solid wood, this would be achieved with good chisels which is why the other threads put me in mind of this question.

Thanks- Aaron

How thick is the plywood. I've done it in 1/4" plywood with a utility knife, a minute or so per notch. Use a new blade, change it regularly.

Cheers,

Bobby

[potomac]

How thick is the plywood. I've done it in 1/4" plywood with a utility knife, a minute or so per notch. Use a new blade, change it regularly.

Cheers,

Bobby

Good idea. It's 1/2'' so that might be a bit more time consuming. I think I remember flomo writing about this method, but using it to cut out whole panels of thin ply so he could maintain an ultra-thin kerf and utilize the maximum amount of available ply. I have to admit that the utility knife with disposable blades is one of my goto tools. Might need to add this use to the list. Thanks.

[jonboy]

I have just redecked a runabout in a superficial topcoat layer of 4mm ply (see other threads) and the craft, stanley , utility knife worked fine, so much quicker than a jig saw or even a fine Jap saw, without any rip out or fraying but it was only 4mm! not even 6mm 1/4 " .....

1/2 inch I am betting will be impossible with any knife, or I'll eat my offcuts.

I have been working with various sheet card, matboard, maquette card, mill board, composites, fomecore etc for years as a restorer and framer and I don't believe you can cut half inch timber with a knife of any kind.
even 5mm kappa line fomecore is a struggle...... in my considered opinion....

[potomac]

I have just redecked a runabout in a superficial topcoat layer of 4mm ply (see other threads) and the craft, stanley , utility knife worked fine, so much quicker than a jig saw or even a fine Jap saw, without any rip out or fraying but it was only 4mm! not even 6mm 1/4 " .....

1/2 inch I am betting will be impossible with any knife, or I'll eat my offcuts.

I have been working with various sheet card, matboard, maquette card, mill board, composites, fomecore etc for years as a restorer and framer and I don't believe you can cut half inch timber with a knife of any kind.
even 5mm kappa line fomecore is a struggle...... in my considered opinion....

I'm sure you are right, jonboy. I've noticed with each progressively deeper cut the blade begins to pinch. I lose quite a bit of finesse as I exert more and more force. In fact, lots of force almost always results in an accident or botched job (I find this in cooking too if using someone's improperly sharpened knives). I do think, however, this is a nice technique to have in your bag of tricks and I think I'll give it a try next time I'm using that expensive 4-6 mm ply.

[hokiefan]

I'm sure you are right, jonboy. I've noticed with each progressively deeper cut the blade begins to pinch. I lose quite a bit of finesse as I exert more and more force. In fact, lots of force almost always results in an accident or botched job (I find this in cooking too if using someone's improperly sharpened knives). I do think, however, this is a nice technique to have in your bag of tricks and I think I'll give it a try next time I'm using that expensive 4-6 mm ply.

When I did it I used a jigsaw to initially cut out the notches to the right depth. But that left the bottoms square, to be faired later. I set up the molds then sprung a batten around them. Trimming out the wedge at the bottom of the notches was a piece of cake. Take shavings not a deep cut, and you get there quickly and with no serious pressure. When the pressure rises at all change the blade, they are cheap. I use a utility knife to the point that it seldom makes it back to its appointed place in the drawer.

Cheers,

Bobby