I hate making jigs. I am not set up for it. I make almost all of my stock by hand, so getting lots of parts carefully dimensioned and then assembled is a pain. Screws? Glue? I stink with these things.
But I made a jig the other day to hold the turned seat rails for grooving them with the plow plane. I’ve done it free-hand with the plow’s fence before, but it has its moments that way. Most plow fences won’t reach very far down the turned stock’s side for support.
This cradle will hold either turned seat rail; those with turned tenons, or those with rectangular tenons. It’s just over 1 3/4″ inside, so I can hold rails that are either just a tad too thick, or thin. Or even those that are just right. If it can wiggle in there, I shim it with 2 wedges. It’s important to use 2, so I can keep the centerline of the rail centered within the jig. So one on each side of the rail.
The front end of the jig has a small block in it that supports the rectangular tenon at the right height for running the plow plane. There’s a hole bored in this for the turned tenon, then the block is sawn apart so it’s only 1/2 the height.
Here’s the rectangular tenon sitting on top of that front end:
And a turned tenon nesting in the half-hole, You can also see the centerline scribed along the top of the seat rail:
In use, the plow plane’s fence rides along the outside of the box/cradle. I had scribed a centerline down the length of the rail, and set the fence accordingly. The back end of the cradle is held under a holdfast to keep it steady.
A good result – the groove is perpendicular to the rectangular tenon, just as it should be.