I’ve watched a 2012 YouTube video of Paul jointing the corner of a mitered picture frame with splines. I’ve been able to replicate the corner but it’s weak. By this I mean I can pull the inside corner of the miter apart; also, sometimes the splines crack. Any suggestions on making a solid mitered corner with splines?
I’ve made several picture frames and oddly enough I find the splines to be the most challenging part. Did you watch the picture frames series on this site? If not I strongly suggest that you do.
1 – use a saw with a wider kerf to make the slots. It’s easier to make thicker splines and also thicker splines don’t break as easily
2- put a small bevel (Paul calls it a leading edge) to your splines. Again, the picture frame video series will explain this better than I can.
3 – to get the splines to the correct thickness I glue it (double-side tape) another block of wood, put my plane upside down in the vice and then run the spline over the plane blade until it’s the right thickness. this will take longer but at least I get predictable results this way.
4 – take a scrap piece of wood and saw a groove in it using the saw you intend to use for making the slots (see step #1). Use this groove to test your spline thickness.