Splines...

I wanted to attach a frame to a chess board with nothing visible on the outside this time. Considering that doing blind dowels meant drilling before assembly, it would have removed the fiddle factor. Instead, I decided to do splines, in order to be able to slide the pieces around a bit to settle them into perfect alignment.
Now that the clamps are off and it looks fine, I'm second-guessing my splines. That worked so incredibly well, that I expect to use this technique often. Hence the questions...
As background, I have a thin-kerf blade with a 1/8" kerf. No dado set.
Firstly, is a 1/8" spline thick enough to be useful? (The pieces will usually be some flavor of 4/4 stock glued edge to edge.) I'm especially wondering if this is enough to hold cantankerous pieces at bay during a wide glue-up.
Secondly, I have a bunch of three-layer junk mystery plywood that I found inside a furniture box. It's a little less than 1/32" shy of being 1/8", and isn't quite a tight fit in the slot, but it has three distinct layers so should be better grain-wise than using some kind of solid stock. Is ~1/32" undersized too loose for a good fit, or should that be OK? Seems like I'm probably pushing what a glue layer can do here, but maybe you can make me feel better about using the rest of the plywood for this.
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Michael McIntyre ---- Silvan < snipped-for-privacy@users.sourceforge.net>
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Usually, 1/8" is considered full kerf, thin is more like 3/32". I'd check that.

It can be. It depends in the size (not just thickness) of the joined pieces, and the stresses that they are likely to encounter. Also the species matters. Why not try a test joint; let the glue dry completely (24Hrs) and try to pull (push, twist, smash) apart the joint?
Two splines is also an option for added strength.

Although it may be adequate for your application, it is not ideal. Plywood has alternating grain in its plys. Optimally, a spline will have it's grain aligned in the direction of the force that it is designed to protect against. If the spline is at 90 degrees to the force, it will be relatively week, and likely split.
-Steve

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Stephen M wrote:

Never thought of that. It's a really sloppy saw. I'll bet it wallows out to 1/8". It's a "thin kerf" blade, but my typical kerf measures out to right around 1/8", or maybe sometimes a hair more. I'll check this.

4/4 hand planed until it's just smooth. Pieces are about 18", with 15" splines. One big piece (15" wide) and one small piece (.75" wide).

Good thought.

Fair enough. So it's effectively even thinner. I do have them so that the longest grain is running the right way for strength, but that leaves the 1/64" outer layers running the wrong way, so I have a 1/32" spline basically.
Not much of a compromise though, and I'll bet if I use two of them it will be adequate. Until I use up the plywood anyway.
Thanks for the thoughts.
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Michael,
Think about that 3 ply. After you cut the strips to use as splines you will have a strip with 2 ply's of long-grain and the middle ply being short grain, or, 2 ply's of short-grain and 1 ply of long grain depending on how you cut it. At 1/8" thick, you will want all the long grain you can get if the spline is needed for support. As for how thick a spline needs to be is a matter of how it's being used. If its just for alignment, then the ply will work fine.
If you are applying a wide edge board around a tabletop and want the spline to help support the glue joint, then I would be looking for a bit thicker, solid spline material of around 1/4" for a 1" thick board with a 1/2" deep slot in each board to get a better glue surface area.
As for your 1/8" thin-kerf blade... a 1/8" wide blade is a regular blade - not a thin-kerf. If you had a thin-kerf blade, that ply would probably fit a lot better. Last I looked, there really is not "standard" for thin-kerf blades since I found about 6 different listings. Only thing common was that they were less than .125" thick.
Bob S.

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