Spline or floating tenon?

[ScaredyCat]

Ok, so when is it a floating tenon and when is it a spline? Are they both the same thing but using different names?

and if not, why isn't this a floating tenon, it's just like a big domino, right?

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[Phil Pascoe]

I suppose it would depend which way the grain ran - if it ran the length a spline, the width (short grain) a tenon. That's the way I'd look at it, anyway.

 

[custard]

Ignore the names, just think about grain direction and materials.

Assume your example is two pieces of MDF or Plywood, and the "spline" is plywood. That would be a good joint and you could call it either a spline or a loose tenon, some people may call it something else but everyone would know what you meant, and there wouldn't be a problem. Personally I'd call that a spline but the more important thing is that it would work!

But now assume it's two pieces of solid wood. The previous ply spline would fail as it wouldn't accommodate cross grain shrinkage. If you made the spline from solid wood with the grain along the length then the joint would also fail for the same reason. The only way the joint would work in solid wood is as follows (the red lines indicate grain direction),

So the solid wood "spline" is now cross grain, and therefore will shrink and expand along with the two components. I'd now call this a "loose tenon", but it's not a big deal if you called it a "spline". The name is pretty trivial, what counts, as I said previously, is grain direction and materials.

 

[ScaredyCat]

So if I was joining two pieces of plywood using a hard wood spline/tenon as long as I allowed for expansion and contraction I could do it but I'd still need the grain of the hardwood to run in the same direction as per your image? The problem being as the two pieces I was joining got wider I'd need wider and wider hardwood boards to cut the spline/tenon from. Hence the existence of the Festool Domino and dowels as a method of joining boards? Or is that irrelevant because the ply board is stable (ish) and I could use the spline with grain running in either direction, provided I allowed for expansion/contraction of the spline depending on if I was presenting end grain or long grain to the joint?

My thought process was essentially route a dado the thickness of the spline, most of the width of the ply. One on the face, the other on the edge and then slide in my hardwood spline and glue up. Logical or is that just a waste of effort compared to rabbeting one board and glueing the other in to that?

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[Racers]

You can cut the spline at 45deg across the board it gives you 1.4142135 times the width, approximately ;-)

Pete