How to get nice corners on a plywood box.

I am going to build a couple of cajon's for my sons for Christmas. These are basically a plywood box with 6 sides with a hole for sound that is used as a drum. If one does a google image search for "cajon drum" you will see many fine examples. But they all appear to have nice sort of rounded corners and edges. They are made in some variation of plywood generally 1/2 and 1/4 inch. Does anybody have some good tips on how best to get this look when joining plywood? I will be using Birch, probably 1/2 in for the sides, top and bottom, 1/4 inch for the front and back.

Thanks, Jim

Reply to
jtpr
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Jim, I assume you're trying to avoid tearout. I use two methods. The best is to use a piece of sacrificial wood and cut both pieces at the same time.the tearout occurs where the blade exits the wood on the cut. A little experimentation will show you what to do. The second method is to use duct tape over the cut (prior to the cut), which is removed after the cut.

Also, make sure you use a good blade that is sharp.

jtpr wrote:

Reply to
Never Enough Money

Jim, I'd use a 1/4" round over bit in a router to ease the edges and corners.

DonkeyHody

Reply to
DonkeyHody

My Suggestion: A hexagon is 360 degrees divided by 6 sides = 60 divided by 2 = 30 degree cuts. I'd use the very high grade plywood I could buy (has better interior layers). Cut very clean angles using a good blade at 30 degrees. You will need a spline in each joint or it will not have very much strength (1/2" ply doesn't have much glue area at the joints). This will require a jig to run each side through the table saw to cut a dado at 90 degrees. Glue up and lightly sand corners being careful not to sand through the top layer.

Reply to
Tom H

Actually when I googled, I saw only 4 sided boxes plus a top and bottom. I would use a solid corner with rabbeted sides so the plywood would fit flush. The exposed corner of the wood could be rounded much cleaner than trying to round off a piece of plywood. I made a chest this way and it turned out nicely.

Reply to
Gerald Ross

You can build them? I thought boys were born with them, no?

Reply to
Edwin Pawlowski

I like TomH's idea best so far.

Reply to
Robatoy

Box joints, rounded over after assembly, are tough to beat IMHO.

Lew

Reply to
Lew Hodgett

Wow, thanks for all the ideas. I guess it is a four sided box with a top and bottom. That's kind of what I meant by six sides. Anyway, this is a picture of what I would like to end up with:

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at the edges on this it appears that DonkeyHody's suggestion would come the closest to the edges in the picture. Do I assemble and glue up then run the router over the edges? Any technique here to avoid tearing? I'm gonna use A4 Birch, seems to be the best I can find in my area.

-Jim

Reply to
jtpr

Thanks, Jim, but actually I like Gerald's idea better. If you have the tools and skill for it, glue a 1/2+ X 1/2+ strip of some contrasting wood to the edges of half your pieces. Let it stand a little proud on the surface that will show. Then glue your box together so you have these contrasting solid wood strips at each edge. Use a top bearing flush cut router bit to trim the edges flush with the plywood, THEN use a 1/4 round-over bit to soften the edge. It will look much better than the rounded-over plywood.

But if you choose to just round the edges of the plywood like I originally suggested, the only tearout problem you will have is at the corner where you begin to go across the grain of the surface ply. Do the edges that go with the grain first. Then, on the cross-grain part, start your cut about an inch away from the corner and go backwards (climb cut) that inch back to the corner. The 1/4 bit won't grab enough to take the router away from you like a more aggressive bit might.

Good Luck with your drums.

DonkeyHody "If thy neighbor offend thee, buy each of his children a drum." - Ancient Chinese Proverb

Reply to
DonkeyHody

Would this be an example of what you are talking about?

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it is, I like it. But if I'm using 1/2" ply on the top, bottom, and

2 sides and 1/4" on the front and back faces, as advised by drum builders, wouldn't this be tough to accomplish?

Actually, now that I think about it, I would only have to do this on the 2 sides and the top...

-Jim

Reply to
jtpr

Baltic birch may be the better choice, it is birch all the way through, most cabinet plywoods have poplar interior veneers. Luthiers use plywood that is all hard maple, there is a luthier newsgroup under the rec.crafts hierarchy.

Reply to
fredfighter

Jim, I was thinking the whole box would be 1/2" ply. If two sides are

1/4", you have to get more creative. I don't have a ready idea for that. Let it ferment a while.

DonkeyHody

Reply to
DonkeyHody

Looks like I misunderstood the question.....Sorry.

Never Enough M> Jim, I assume you're trying to avoid tearout. I use two methods. The

Reply to
Never Enough Money

Reply to
Tom H

I will post a drawing on Alt.binaries.pictures.woodworking showing what I was talking about. The rabbits can be done with a jointer, router or even with a table saw. After sanding level I then round over the corner. Good luck, however you do it.

>
Reply to
Gerald Ross

I just found this site. This is exactly what I am trying to achieve. But without the internal snare stuff...

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sent him mail.

Reply to
jtpr

Yes

Mount router in table and use fence with rounding over bit to insure that your piece is following a straight reference (fence) rather than use a bit with a pilot bearing and allowing the bit to follow the assembled edge.

When starting at a corner, include a sacrifical piece to avoid tear out.

Have fun.

Lew

Reply to
Lew Hodgett

You're right..and they're quick too...and easy to assemble.

Reply to
Robatoy

Here's our first attempt

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corners were mitered with biscuits, then hand planed at a 45 degree angle to ease each corner, after staining.

1/4" is too thick for the drum "skin". Use 1/8" baltic birch. We used all baltic birch, 1/2" sides, 1/8" drum skin and 1/4" back.

The cajon we built has an awesome sound. We paid a lot of attention to making the joints air tight.

Bob

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