Mortise Paring Jig


I needed a shop appliance that would help me pare out the sides of a mortise and maintain the proper angle to guarantee square sides.

Being a newbie when it comes to mortise and tenon joinery and the art of hand tools, I need all the help that I can find...

I had seen a jig in David Jeske's blog at the Blue Spruce Toolworks site. I liked his jig, shown below, and my design ideas went from there.

I created a quick drawing in Sketchup...the idea was to have a lower piece that could be clamped to the workpiece. Then the upper plate would slide out to line up with the wall of the mortise.

The adjustable top could then be secured and a paring chisel could slide along that surface to level out and square up the walls of the mortise.



The wood selected for the project was 12/4 hard maple.

I marked out the grooves for the hardware, cut the sides with a 14 inch Grammercy sash saw, and then used the LV large router plane to hog out the grooves to the proper depth.

The slots for the hardware were made by drilling a series of holes, this was done at the drill press with lipped brads.

Here is the drilled hole lineup...


A paring chisel was used to smooth out the sides.

This is the exact type of paring task for which the jig is designed.

The final smoothing finish for the sides was done with a Lie-Nielsen face float.
The rounded ends of the slot were finished out with an Auriou modeler's rasp and rat tail rasp.

The hex head bolts screw into threaded inserts.

There was a hardware failure during the insert install, the screw slot broke off. I had to do some wood removal to enable the unit to slide properly

I should have used the steel insert instead of the brass model.


Here is the finished jig ready for a test.
Here is the test...using the jig to guide a 1/2 Ray Iles mortising chisel.

As a further design development...we put a 4 degree bevel on the end of the jig.

This is to be used to put a bevel on the wall of a mortise so that it can be used effectively with a through tenon that is expanded by wedges.

This image illustrates how the wedge expands the through tenon to lock it into place.

The jig end is being used to create the "tapered mortise" shown in this image.

The strain-relief hole provides flexibility so that the inserted wedge may expand the tenon into the space created by the tapered mortise wall.

Here a paring chisel is laid flat against the bevel and thus is following that 4 degree end to create the tapered mortise wall.



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