Sunday, 8 January 2017

Infill Plane: Design Phase

The first of what I assume will be many sobering moments in this process occurred shortly after my post about having finally acquired the materials for constructing an infill plane.  Now that I would be able to start building the plane, I realized that I hadn't given much thought to just what I was actually going to build.  It was time to calm down and think about what I was going to do.

The thing that had touched off this obsession with building an infill was an article in the August 2006 issue of Shop Notes (Vol. 15 Issue 88) that featured the building of a dovetailed infill shoulder plane. Though it was tempting to follow the plan, the plane used a 2 piece sole and had an adjuster that needed a special blade to work.  This put it a little too far outside my comfort zone for a first attempt.

What I really wanted to build was a smoother.  Something with straight, not curved, sides.  Something simple, but with a closed tote at the back.  Something based on a traditional plane, but with enough different elements to be my own design.

If this were a movie, there would now be a montage of me hunched over my desk until all hours of the night, crumpling papers and snapping pencils in frustration until finally arriving at a glorious design after some divine inspiration.  In reality it was a little different.  There was some paper crumpled, but progress was steady until I arrived at this:

It's based on the Norris #6 smoother.  It shares the parallel sides and closed tote, but the sidewalls are decidedly less curvy.  This appealed to my desire for a simple, clean design.  The tote is about 1/4" too far back to my eye, but this was the general idea, and from here on it was about refinement.

The purpose of this post is to remind myself of the choices I made and the reasons behind them, so I want to talk a little bit about some of the choices I had made at this point.  Keeping the top line of the sidewall consistent in front of the lever cap and behind is the one thing that makes this design mine. Most infills swoop down and then rise up again in front of the blade, and the top of the sidewall is flat at the front bun.  Another idea that I toyed with but didn't include was to change the angle of the front so that it was 90 degrees to the top of the sidewall.  The idea was to make it look like one of those art deco inspired steam engines, but I couldn't quite pull it together and it wound up on one of the crumpled pieces of paper.  Maybe another time.

Another advantage to a simple, mostly geometric design was that I could easily transfer it to a CAD program and work out design details there.

The first thing I wanted to establish was the placement of the cross pins that hold the infills in the body.   This is something that seems to be an afterthought on a lot of infills and I think that it detracts a little from the overall effect of a well designed plane.  I wanted to keep the lower front pin in line with the rear pins.  I also angled the line a bit downward from front to back.  In the drawing above, I tried to make the angle the same between the front pins and the lever cap pin and the second pin.
It didn't look right though because it made the spacing between the lower pins all wrong.  The front pin is too far forward as well.  One last thing I took away from this drawing was that the 1/4" pins looked too big to use for holding the infills in place.  I switched them to 3/16."

After making those changes I added some dovetails and did some rounding at the ends of the sole. The front corners have a 1/8" radius and the back end is almost semi-circular.  The vertical lines near the back end are where the curve would start and the end of the sidewall with that curve.  I felt good enough about this to trace in the rear infill and tote.

It was here that I discovered my mistake.  When I had done the first sketch, I had set the mouth 2" back from the front of the plane.  In  the CAD drawing I had gotten confused and set the back of the mouth at 2".  What this did was solve my problem of the rear tote being too far back.  When I looked at the whole thing, however, it seemed to be dominated by the big hole in front of the rear tote.  The rear dovetail was also too far away from the back of the plane.  Back to the drawing/keyboard.

This is the final result.  The mouth has been moved back 1/4", which closes up the tote and eases the angle of the front bun.  All the dovetails have been moved back 1/8" and the radius of the curve of the rear sole has been enlarged so that the distance from the front to the first dovetail is about the same as from the rear dovetail tithe end of the sidewall.  I also changed the area around the lever cap pivot pin to be more like the original sketch.

There is a lot to do yet.  The lever cap is only a roughly sketched in, and the cap screw is barely an image in my head due to the technical challenges it presents (By the way, does anyone want to loan me a metal lathe and teach me how to use it?).  This is enough, though , to get started.