Friday, September 22, 2017

The Tale of Goldilocks and the Three Rabbets

"My rabbet moves further into the vertical wall with every plane pass," said daddy woodworker.
"My rabbet gets further away from the vertical wall with every pass, creating steps," said mommy woodworker.
"My rabbet is juuuust right!" said baby woodworker.

I've been doing some practice work with mouldings.  And when you use hand tools, that means cutting lots of rabbets.  When using a rabbet plane or a shoulder plane to cut rabbets, the iron should be just a little proud of the right side of the plane.  But how much is enough / too much?

Here is my shoulder plane.
The shoulder plane
The iron is proud of the right side by about 0.004".  This is not easy to measure, so I used a piece of 0.0025" thick paper to guestimate the amount.  The iron was more proud than one thickness of the paper, but just less than two thicknesses of the paper.
View from the plane's sole showing iron just proud of side
I used a wheel-type marking gauge to mark some poplar for a 1/8" wide x 1/4" deep rabbet and started the cut by setting the edge of the shoulder plane in the gauge line.
Starting the rabbet with plane edge riding in gauge line
Creates a little tiny shaving on which I can see the pencil mark I added to the gauge line
Right away it seems like it's cutting into the keeper wood of the vertical wall.  After two or three passes like that I was already into the vertical wall by about a millimeter!!!!  Holy crap, that went south fast!
Arrow points to the "new" vertical wall location
I continued with the plane held vertically and the plane cut fairly vertically - that is, I didn't keep moving the wall to the right.
Abandoned the first rabbet and gauged another line for 1/4" x 1/4" rabbet
For the next experiment, I nudged the iron to about a 0.002" proud of the side and started the rabbet as I did before by tilting the plane in the gauge line.  This time I did not move the gauge line very much at all, but it did move a little bit.
Stayed very close to the vertical line
Looked very good at the far end, too
I continued the rabbet to completion and I needed to clean up the vertical wall a little bit.
Vertical wall needed a little bit of cleaning (with shoulder plane on its side)
Well, this looked very promising, so I did another test with a board marked for a 3/16" x 3/16" rabbet.
This came out very good with little or no clean-up needed
The far end looked good, too
I have a Record rabbet plane and wanted to try using it for these experiments, sans fence and depth stop.
The Record #778
So I set its iron about 0.002" proud of the right side and gauged another 3/16" x 3/16" rabbet.  I angled the plane in the gauge line like I did with the shoulder plane, but got a very different result!
(Ignore the chipped corner)  The first pass got me way past the gauge line!
After a couple passes I was not even in the ball park.
I think the reason for this is that the Record rabbet plane has a significant chamfer on the edges of the sole, so it doesn't ride well in the gauge line.
Edge by my thumb nail is chamfered
So for the next test run I started the rabbet with the shoulder plane with its iron 0.002" proud.
Started rabbet with the shoulder plane ...
... and finished it with the Record to remove material more quickly
Nice square rabbet, but went past my vertical gauge line at the beginning ...
... and at the far end
My final experiment was not really an experiment, but a different technique altogether.  I used the shoulder plane to start the rabbet away from the gauge line, using my left hand fingers under the sole as a fence to keep the plane just a little away from the gauge line.
Plane held vertically, left thumb on top, left fingers under sole acting as a fence
This is easier than it sounds.  After a few passes, I was deep enough ...
About 1/32" deep
... to switch to the #778 for faster (and more comfortable) material removal.
After I got to the depth line, ...
... I cleaned up the vertical wall with a few passes of the shoulder plane
It's very easy to sneak up to the exact vertical gauge line that way ...
... and get a perfect rabbet
Matt Bickford espouses this last method.  It's easy to get it perfect after practicing once or twice.  On wider rabbets it can be tougher to start the plane, but you can still get a perfect rabbet.

The moral of the story is that if I want to cut rabbets, having the iron about 0.002" proud of the side is probably about the right amount.  But I can remove all doubt by rabbeting a little away from my vertical gauge line and cleaning up the vertical wall with a few strokes with the plane on it's side.

And Goldilocks said, "What nice rabbets you are!"  And they all lived happily ever after.