Preparing small tabletops or irregular-shaped tops for finishing can be difficult with handplanes. If the top has a lot of mass, you can usually count on friction to help hold the top in place. Or you can screw it down from the underside , assuming the underside is not a show surface.
But sometimes the best solution is to make some cauls to grip your work, which is what I did this morning in the shop to plane the top of some 18″-diameter tabletops for the next issue of Woodworking Magazine. The cauls are made from the scrap parts that fell off when I cut the tops to rough shape on the band saw.
Then I skipped the scrap pieces through my planer to reduce their thickness (I also could have used a jack plane). Then I bored 3/4″- diameter holes in the cauls so they would press-fit over my 3/4″- diameter round dogs in my benchtop. Finally, I pinched the top between the two cauls using my wagon vise (though any end vise can do the trick).
When I’ve done this on workbenches with square dogs, the solution is to cut the pointy end of the caul so it is flat. Then you brace the flat against your square dog.
No matter how you rig your cauls, pinching the work between two cauls has some advantages, as long as you don’t use too much pressure. With two cauls you can rotate the top to work cross-grain if necessary or move the top so it’s more convenient to plane.
This arrangement works great with belt sanders. It’s not necessary if you use a random-orbit sander to prepare your work. Then you can just place the work on a blanket and get to work.