I had a door that was not shutting properly. It was a little tight on the edge and my wife kept after me about fixing it while I was trying to mull over the solution to the problem of how to prop up the door while I planed down the edges.
Finally, I devised these door dogs so that I could support the door in my shop while planing the edges. They’re large braces, but the interesting fact is that the feet cause them to lean inward. This means that the uprights pinch the door tight and lock it in place while my plane does its job. The specific dimensions are not important, but they’re roughly 12" × 12", with carpet padding on the uprights.
Ted's Woodworking - Guide eBook