WoodNet Forums: Does a chipbreaker really break chips?

The Old catalogs that I can find, mostly support your arguments. I don't however find top irons particularly hard to make, but then I make them for wooden planes and don't have to worry about the drilling, slotting or tapping involved.

In the old catalogs, the specialty planes don't have chip breakers. Even the fancy ones. The more expensive bench planes, by shape, handle or material do.

In the Barton Mack 1910 Catalog, the Single Iron Razee Jack is $110 the Double Iron is $120. Tthe better smoother, jack, block and jointer and fore planes are all double ironed. So for them, the addition of a double iron was more expensive, but not prohibitive.

In the Melhuish 1925 Catalog, a few rabbets have double irons, but the scrub plane does not. The irons sell for more than the top irons, and cost more if they are larger. The top irons have a flat price.

I seem to recall a catalog with york and middle planes in it, but I am not finding it anywhere. As I recall the higher angle planes do not incorporate chip breakers. This would support my observation, but I cannot find this evidence right now.

Here is a bit of interesting data I just found while looking for plane catalogs, from the 1856 book, Turning and Mechanical Manipulation by Charles Holtzapffel, From The section discussing double irons.

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The constant employment of the top iron in all available cases, shows the value of the improvement; and the circumstances of the plane working the smoother, but harder, when it is added, and the more so the closer it is down, demonstrate that its action is to break or bend the fibres. This is particularly observable in the coarse thick shavings of a double-iron jack plane, compared with those of the same thickness from a single-iron plane; the latter arc simply spiral and in easy curves, whereas those from the double-iron are broken across at short intervals, making their character more nearly polygonal; and the same difference is equally seen in thinner shavings, although of course less in degree.

Fig.326 represents the iron of a plane intended "for the use of cabinet-makers and others, who require to cut either hard or coarse-grained wood," the upper bevil given to the iron, being considered to dispense with the necessity for the top-iron; but it is obviously much more difficult to produce a true right-lined edge, by the meeting of two planes, each subject to error in sharpening, than when one exists permanently flat as in the broad surface of the blade.*
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While his first argument is that a chip breaker does indeed break chips, the blade modification he describes as an alternative for a chip breaker, is specifically intended for hard or coarse grained wood. He also indicates that the closer the top iron's edge is to the cutting blades edge, the greater the action of it.

Since my personal observation is that the chip breaker helps with harder wood, It is nice to find an old source that tends to support my observations and hypothesis.

Bob

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