Thread: In search of perfect curves...

On a plane, that is..

Curves on metal planes serve both practical & aesthetic functions. Looking at a plane from the side, the dip behind the front bun opens the escapement area up more, allowing shavings to spill out (or be flicked out) more easily. But then the sides need to be raised to provide a place to locate the lever-cap axle. These are “practical” curves, others may be added purely for decoration: 1.jpg

Then of course, there are various curves on the woodwork. The curves of the rear stuffing can have quite a big effect on overall appearance. For my very first infill, I was influenced by saw handles when sculpting my handle & it got a bit fussy. Old infills tend to have a more simple oval finger hole. 2.jpg

You can also apply curves in another plane, i.e. to the sides of the sole rather than having straight, parallel sides. A common shape applied to smoothing planes was the so-called “coffin” shape, where the toe curves in a little, while the rear tapers to about the thickness of the handle. 3.jpg

On my first infill, I decided to give it curved sides, which was not the smartest decision given my state of ignorance of metal plane making. I had many anxious moments trying to bend the sides to the sole shape, but my main mistake was in not fully appreciating how the curve of the sides could impinge on lever-cap function and lateral adjustment of the blade. With #1, the front curve starts a little too soon and the toe of the lever cap had to be rounded a bit to allow it to rotate freely. (I’ve since seen several old infills with similarly-shaped ends on their lever caps, so my ‘design flaw’ is far from unique.

Curving the sides in too soon or too much behind the mouth can create another problem; it may restrict lateral adjustment of the blade. This happened to me with this small rear-bun smoother: 4.jpg

I began the taper too far forward, so the body is a couple of mm narrower than the maximum width at the point where the blade emerges at the top. I had to grind a small taper on the top half of the blade to allow adequate lateral adjustment of the blade: 5.jpg

For my second (handled) infill, I was more aware of matters curvaceous, and I made sure the side curves began in front of, & behind, a longer near-parallel mid-section. 6.jpg

There are no problems with cap-iron rotating freely, and plenty of room for lateral adjustment of the blade assembly, but I had two different issues arising from curves. First, I put too much & too sharp a curve on the toe end. 7.jpg

Then I didn’t fair the start of the curve sufficiently, and with the bend commencing right at the lowest point of the dip in the side, when I pressed it in the bending form, it wanted to kink rather than form a curve. I smoothed it after peening, but an oblique light shows up more of a corner than a smooth curve (arrows). 8.jpg

It’s a detail that only a fusspot would notice or bother about, but there’s no “fix” once the body is peened up.

About the same time, I made another, slightly smaller smoother. I was mucking about with screw adjusters and made a version of the “Norris type” adjuster. I reckoned I could make it work a bit more smoothly than the Veritas by changing the screw pitches on the shaft. The Veritas version is a lot simpler to make but it requires a blade with holes to engage the travelling spigot of the adjuster. A Bailey blade has the long slot for the cap-iron screw to slide along, so if I wanted a 1 ¾” blade I would have needed to either fill in most of the slot, or make a blade from scratch. My heat-treating skills are still very rudimentary, so instead, I used a Veritas blade with adjuster holes already in it. The easiest blade to get was a block-plane blade but these are only 41mm (1 5/8”) wide, so my plane got a little skinnier than originally planned. For this plane I copied the side profile from a picture of an old Spiers (Mathieson used an almost identical profile & I don’t know who was first - perhaps neither). 9.jpg9)

I worried that the narrow body would make it look rather skinny & unstable with a full body curve, so I left the front parallel, & tapered the sole from behind the blade-bed area. I’ve seen several old infills with a similar shape, but they were much wider, and somehow the wedge shape suited them far more than it does my skinny little thing – it looks like it has missed a few decent meals! 10.jpg

But would you believe it, this is the best-performing infill I’ve made so far, it feels solid & sound & takes any wood in its stride. No other plane I have would go on making tear-free shavings on this piece of Solomons ebony (possibly the most difficult wood to plane I’ve ever encountered), like this plane did: 11.jpg

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