Wooden Plane Throat Geometry

I've been thinking for a couple weeks about how to write this post.  There are certain aspects of throat geometry that are very difficult to photograph, and without decent pictures it's tough to describe.  So I'm going to try this with a combination of pictures and Sketchup images.

I'm not an expert on wooden planes.  Most of the woodies I've used are ones that I've made.  I know there are MANY different wooden plane geometries out there.  I'll write about one aspect that you may not know about until you've studied these planes.

To do this I'll first show in sketches a sequence in making a wooden plane.

First, the bed, breast, wear and abutment lines are laid out on the plane blank (toe at left)

... and those lines are continued across the top (and also the sole)

Note that there are two sets of lines going toe-to-heel on the top of the plane blank.  (Those lines should also be drawn on the sole within the mouth area, but I had not done that when I exported the first pic above.)  The inner lines mark the innermost extent of the wedge abutments.  The outer lines mark the depth of the abutment recesses and, on the sole, they mark the overall width of the mouth.  One method of constructing a wooden plane is to excavate to the inner lines first, and that would look like this:

Primary excavation

And here's a birds-eye view

Currently, the mouth is not wide enough to fit the iron.  Then material is removed for the abutment recesses.

Abutment recesses formed

You'll notice that these recesses extend all the way to the sole.  The lines laid out on the sole to mark the lateral extents of the mouth guide the plane maker to end up with flat abutment recess walls.  The total width of the recess for the double iron and wedge is the same as the width of the mouth.  This is about 1/16" greater than the width of the iron, and that allows a little wiggle room for the iron to adjust its edge parallel to the sole.

To aid in removing shavings from the throat, some wood is chiseled away forward of the abutments.

Throat widened towards front

The throat is widened nearer the front of the plane.  The abutment line connecting locations 2 and 3 is unchanged.  The location at "1" is taken down to the same depth as the abutment recess.  Later, the "eyes" are carved into the edge that joins locations 1 and 2.  I can't do that with Sketchup, so I'll show a real pic.

Arrows show locations of the "eyes"

OK, now I'll introduce the wedge (shown in red) and the double iron to this picture.

Wedge and irons added to the picture

And here is a zoomed-in view of the area near the "3"

The (initially too long) wedge is cut off at the location where the cap-iron starts curving down to meet the iron.  Then the two lower ends of the wedge are tapered.  This helps to steer shavings towards the center of the plane as it cuts.  The taper begins just to the right of the number "3" in the above picture.

You can see the tapered ends better in this solo sketch of a wedge

As it stands in the pics above, the area of the plane body near the "3" could cause shavings to get jammed between the abutment and the wedge, so some material needs to be removed, just like the tapered end of the wedge.  I've tried to draw this in Sketchup, but it's tough due to many odd angles.  Hopefully you get the gist.

Some material below the "3" removed to match the taper of the wedge fork

The combination of the taper on the wedge fork and the taper on that part of the plane body will force shavings to the center of the throat.  Any discrepancies in this area - places where the tapers don't mate well - are places where shavings could get caught and cause a jam when using the plane.

In the following picture, hopefully you can see the area that was removed just forward of the tapered part of the end of the wedge.

The shadowy area down in the throat is what I'm describing

This is just one seemingly minor aspect of wooden plane design and fabrication that is not readily apparent to the novice plane user/builder.  But it is critical to the performance of the plane.  As I've found out, it can be tough to get a chisel in there to remove that material and create a smooth transition between wedge taper and plane body.

Next week I'll post about making two wooden smoothing planes - a prototype and the real deal.