Hand Tools Archive

Subject:
Where did the ball go?
Response To:

david weaver
The important issue here is that you will never actually plane with the cap iron below the sole of the plane.

Let's go back to the numbers (I did intentionally suggest that you'll take a shaving thicker than the cap iron is set back, but we need a few assumptions to see why i said that).

Assume (though it's probably not quite right, but it's close) that:
*The set of the cap iron flush to the sole of the plane is 2^0.5 times the deepest depth of the cut in order for the cap iron to be flush with the sole (well, that part's not assumed - it's mathematically correct).
* assume also that the thickness of the shaving will be approximately 2^0.5 times the depth of cut at the deepest point (that's assumed, I'm sure it varies by wood and can sometimes be a little less).

That would yield a shaving thickness that is right around the same as the set of the cap iron (even though the wood removed is the cap iron set / sqrt(2). This, itself, is a losing proposition. In order to get good function out of a cap iron, there is a bit of space on the open back of the iron across which the chip travels before it meets the cap iron itself. that is why larry used to always go on and on about "beam" strength. That's the beam.

In simple terms, I'd say, if you really think cap set at the sole is practical (or especially below), then the next thing to do is to work a quantity of wood with the cap set below. At the very best with the cap set flush, the surface quality will be very poor. At the worst, you won't be able to push the plane (that will be the case with a jack or try plane). This is actually what I first did when I set a cap about a decade ago, and concluded it made the plane too hard to push and set it aside. Of course, I argued that with Warren (who else would have been arguing? Nobody else did at the time).

We set the cap back a little extra from the sole so that the shaving can be cut cleanly, and so that we are not smashing the wood fibers ahead of the cut, which is what will occur if the cap is set flush with the sole of the plane. The consequence of this smashing is a smashed looking surface - try white pine if you really want to see it. Warren could spot that in a second (shiny wood that has a rippled look because it was crushed), and so can I.

That is a very important point, because that's what leads to there being no need to trim the corners of a cap iron (well, except when there is a plane that does not have a flat sole like a gutter plane, but those cap irons come radiused from the maker) shy of the wood, and by clipping the corners, you are going counter to what you'd actually do to reduce tearout, which is to set the cap closer to the sole of the plane for a thinner cut.

Now, feeding (clogging is a term most people will probably use) in a wooden plane is something entirely different. If Nicholson would have contended that most feeding problems are in the corners (they are) in a plane that is not properly set up or tuned, certainly that could be a legitimate reason (maybe nicholson did - I haven't read it). I am out of context in that, because I worked hard - even as an amateur maker - to figure out what keeps a plane from having feeding problems at the corners without just completely opening up the wear area and eliminating it like a stanley plane done by incident. When I make a wooden plane, if it has a feeding issue, probably 90% of the time, it occurs at the corners, but I have gotten better at identifying what wear will go with what cap iron profile (for example, a long flat ward cap iron will be more forgiving, but an early rounded butcher cap iron with a lot of curve and spring - not so much. The wear angle needs to be steeper on an otherwise identical plane).

All of that is why this is at best a lateral move, but potentially worse. If the shavings at the (side) edges of a cut are so thin that they can't tear out, no harm done. But a lot of pointless work has been done to tune this, it can't be reversed (which may really not matter, especially in the case of someone like warren who is not going to put a plane down until it's completely worn out - my obsession with residual value and ability to reset doesn't apply). Warren is the first person who actually understands the cap who has mentioned this. I can't really argue that he shouldn't do it - why should I? I'm sure he's a better woodworker than me.

I would suggest that nobody else who is new should do it because they don't understand caps that well, and that of others can set their planes up correctly, they'll find no benefit from it. And in that, I'm quite sure (I'm an actuary, I never say 100% anything - but let's go 99.999%) if Nicholson thinks there is, I'm right and he's wrong.

I've got a bunch of work to do today, maybe I'll revisit this tonight. Do try the cap iron set below the sole, even a little bit.