Are spline joints inherently stronger than a standard butt miter joint?

Question

I have always liked how spline joints look, but I was unsure whether it would help or hurt the joint strength. Are splined miter joints stronger than other types of mitered joinery?

Answer 1

Yes, they are stronger Splines increase the surface area being glued,; and thus the strength of the joint. And since miter is close to being end-grain to end-grain, it can definitely benefit from reinforcement.

Not necessary in things which aren't under much stress, like small boxes and picture frames, but as you say splines can also be a decorative element.

(For large picture frames, there's a cute variant of a lap joint which looks like a miter from the front and provides lots of long-grain contact. Not that I've tried it yet.)

Answer 2

Not certain which joint you're referring to:

But regardless of whether you mean a true splined mitre or a keyed mitre the reinforcement does add to the joint strength.

Both increase joint strength due to three factors: structural advantage, the thickness of the wood slivers used and the glue surface area. When considering splines or keys of conventional size — roughly as in the illustration above — the splined joint is superior in all regards (being both physically stronger and providing greater surface area).

It should be mentioned, there are numerous other ways to reinforce a mitre joint, from nails driven across the joint at the most basic, through to dowelling (both hidden and shown) all the way to a few variations of blind dovetails.