Saturday, April 19, 2014

Skew mitre plane: the mortise

Not much time for planemaking or blogging lately, but I did make some progress on the mortise.
Chopping the mortise was not really more difficult than with an unskewed plane--just more time-consuming.
As usual, the first step was to make a guide block for chiseling. I just used a piece of southern yellow pine scrap. I laid out the lines, cut it with a handsaw, and then did lots of careful planing, checking frequently with my two bevel gauges (set at 38° and 20°) and a straightedge, until the angles were perfect and the surface flat.

Here's a completely phony, posed shot, taken after the fact, that shows how the guide is used.

I generally chop freehand until I get within about 1/4" of my front and rear layout lines, then use the guide to finish off. Here's the mortise roughed out:

Then I use a flush cut saw to widen the bed and define the abutments. The bed cuts are simple--i just lay the saw on the bed and cut 1/4" deep. For the abutment cuts, it helps to make a spacer block. This was the first point in the project where the geometry got a little tricky. My first attempt was a failure, but it helped me figure out the correct the angles. The main angle is 10°--a standard wedge angle. But the skew is not 20°, because I'm referencing off the 38° bed, rather than the sole of the plane, and this decreases the skew angle. I suppose I could have figured this out with trig, but in practice it was easier to just do a little trial and error. The final skew angle turned out be 15°. The sides of the spacer block are angled at around 10° (relative to the bottom of the block) to match the sides of the mortise. Anyway, here's the spacer block:

I shot some Spray 77 adhesive on the back of the block to temporarily hold it in place for the saw cuts. After I was done, the block was easily removed with a few hammer taps.
Finally, I chiseled away the waste between the saw cuts. Here's a shot of the more-or-less finished mortise:

I've got some stupid cosmetic scars on the bed (from chiseling the abutments), but the cutting iron won't care. Overall, I think it's looking pretty good. The next thing is to deal with the iron.

Tuesday, April 8, 2014

Skew mitre plane: Layout

I'm going to try and do a few posts detailing the construction of a skew mitre plane. I've never built such a plane, so it may turn out to be a total bust, but it will be interesting!
First, some details. The plane I have in mind is a low angle plane, primarily meant for use with a shooting board, but also for planing end grain freehand, with the work held in a vise. I've never had a proper shooting plane--my Stanleys aren't square enough, and my wooden planes are all 50° or higher, so not ideal for a dedicated end grain plane.
This plane will be similar to the Old Street strike block plane--it will be about 14" long with a 38° bed angle--but it will also have a 20° skew, which provides a shearing cut on the shooting board. Phil Edwards (Philly planes) makes a model like this, although his looks a bit smaller. And of course, mine will be a lefty model!
So, on to laying out the plane. This isn't really much different from laying out a "normal" plane. I always start by laying out one side. From left to right, we have the bed, the blade, the wedge, and the front of the throat.

With a "normal" plane, I would then transfer these marks across the sole with a square, lay out the other side, then transfer those marks across the top. If I don't end up back where I started, something went wrong, so I go back and find the problem.
So, for this plane, I do the same thing, just using a bevel set at 20° instead of a square.

The layout on top isn't quite complete--the throat has to flare out so that it's the same width at the front as at the rear. But that's later. The initial focus is on making a trough that is about 1/2" narrower than the iron.
The final layout task, for now, is to mark some locations for drilling. I scribe a bunch of lines parallel to the skew angle, in white pencil so I don't confuse myself. Then I punch centers for drilling.

The basic idea is that all points on a white line will have the same final depth, so I can drill 3 holes before I have to change the depth stop on the drill press. This process is time consuming, but makes chopping the mortise a lot easier.