Miter Splines & Planing Thin Boards
Making Miter Splines by Hand
Why are we making miter splines by hand in the first place? I don't think miter joints are nearly as weak as so many claim. It is a lot of glue surface and not really end grain but more of a halfway between face and end grain. Moreover miters usually imply a complete box or frame and once you "complete that circuit" with the 4th side of the assembly you have quite a bit of strength. But like with any joint it is the twisting and racking that causes them to fail and miters can be exceptionally susceptible to this. So we try to strengthen them by adding a spline of long grain material across the joint. This is common in flat or frame miters and best done by actually gluing the joint first then sawing in your gap and inserting the spline. I show two ways to do this in this video.
But it is the wide or box miters that I think really benefit from the spline. Ironically I don't think a long case side that is mitered needs much strengthening when you think about all of that glue surface. But assembling such a joint is a pain in the butt and adding a spline makes it so much easier. Now the joint locks together and you can clamp the assembly much like you would a rabbeted or dovetailed case. Making a miter spline here can be done quickly and precisely with a plow plane by capitalizing on the angles created by the miter itself. Reverse your boards and you can ride the fence of the plow plane against one mitered face while cutting in the groove on the opposite face 90 degrees to the surface. Now plane a spline to fit and you have a tightly fitting joint that won't slip about when you try to clamp it.
Planing Thin Boards
I'm talking really thin boards. Like less than 1/4". My planing stop and my paring hook fence are both 1/4" high so I can use those for "thicker" stock. But when I need a really thin board, like when making a miter spline, I sometimes need to plane something down to 1/8" thick or even thinner when making inlay. Here the wood is so flexible that it can be hard to hold. My default technique I call the invisible vise which is just a fancy way of saying double stick tape. But this is cumbersome when you have multiple parts to plane and the tape is so strong that sometimes it is nearly impossible to break the piece free without snapping the wood in half. So I show how using a holdfast can solve this problem and how a bit of forethought in the length of your piece will make it an easier task.
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