Hand Tools Archive

Re: I'm struggling to figure out...

Whooaaahh. That video is spectacular. You guys have done a really great service bringing this to us - THANK YOU!!! The papers made all these cases extremely well, but I agree that they were more somewhat less easy to work through (Warren will recall when he schooled me for reading it improperly a few years back).

However - David: your post seems to be suggesting that some of the other plane variables that seem to get much more 'discussion time' on the internet are now somehow less important. It almost seems like you see them as shams now. What the video proves is that a chipbreaker/subblade/cap iron CAN mitigate tearout in some instances - nothing more, nothing less.

For those who don't know me, I make infill planes for a living. So I suppose my analysis may be suspect to some, but I'm going to spell out my take on all this as clearly and precisely as I can so my point doesn't get shot down because of my possible biases.

For those uninterested in the long technical stuff to follow - my only point is to say that the video offers no reason at all to suggest that single-blade planes, higher-pitch angles, thicker blades, and premium planes are any less important, or any less of an improvement. I'd also like to make a somewhat detailed case for what the pertinent variables ARE, and why they matter.

As I formulate it for myself, there are 3 basic factors at work in a plane: the sharpness of the edge doing the cutting, the rigidity of the edge transport, and the fiber manipulations. What this experiment does exceptionally well is to eliminate all of the variables other than the fiber manipulation due to the chip breaker.

I believe the sharpness was held consistent from test to test - I don't remember the mechanism for this as it's been several years since I read the papers, but I'm sure it was dealt with.

Edge transport - in most planes this is essentially concerned with the relationship between the blade and wood, and the consistency of that relationship (which is the relevant detail) is determined by the rigidity and inflexibility of: the plane sole; the mating of the body (sole) and the frog/bed; the mating of the bed and blade; and finally the blade itself, where the type of steel (or laminations), honing angle, and blade thickness all affect how consistently the edge can hold its position.

The edge transport in this experiment was an extremely rigid machine setup guided by a high tolerance mechanical system with, as near as I can see, an absolute minimum of moving parts and joints. The rigidity matters intensely because if the edge moves or vibrates at all the surface will suffer, and the chances for tearout increase dramatically. But in this video, the variable is totally rendered inert because it is completely consistent throughout all the tests.

The fiber manipulations in most planes are either three or four-fold. First, there is the compression of fibers by the sole. Second, there is the range of free movement of the fibers dicated by the mouth opening - larger mouth equals greater leverage available for tearout. Third is the pitch of the blade, which dictates the initial bend angle the fibers must accomodate, which again affects the leverage for tearout, and also how rigid the fibers are (if unbroken, the wood fibers are much more able to lever for tearout). Finally, in blades with a chip breaking mechanism of any sort - be it the lever cap, a cap iron or subblade, or even (potentially) integral chip breaking in the blade geometry itself.

Again - in the video, there is no 'sole' whatsoever, so no fiber manipulation from that. There is also no mouth opening whatsoever, so that is mitigated as well. Finally, the blade pitch is a constant 30 degrees in every case. The only variable is the cap iron pitch and distance from the edge.

All of which is a very long way of saying that the experiment is extremely well designed to suit its purpose. This is what makes it such an excellent proof. Anyone who thinks that cap irons CANNOT affect tearout should change their thinking after seeing this. There may still be valid reasons for thinking chip breakers are perhaps not a particularly valuable strategy - after all .1-.2mm (~4-8 thou) is a tricky setting to master, especially if one cambers one's blades - but that doesn't undermine the solidity of the proof here that chip breaking can work quite well if done properly.

Again - please, let's don't forget that there is nothing in here that negates the importance of any of the other variables I've mentioned above. Blade pitch is still very much a viable means of dealing with tearout. And rigidity - which is probably the main difference between antique or inexpensive planes and premium ones - is also still extremely effective as a way of dealing with tearout. Finally, the other difference between poor and premium planes is in the fiber manipulations occurring via the sole and the mouth opening. Again - these are still extremely viable as strategic points for reducing tearout.

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