Re: FWIW, my results
Dave Mount
>Well, I just tried the experiment for what it�s worth. Given my lack of a quality straightedge, my assessment methods are potentially suspect, but here�s what happened.
Summary: Using a LV low angle jack, I saw evidence of crowning after 10 passes. When I did the same procedure with a smoother (Keen Kutter K4C), I did not observe crowning.
Details:
I used two pieces of stock, one walnut, a full 1" thick and 24" long, the second a piece of yellow birch 3/4" thick and 27" long � no special reason, they were just there and about the right length. I didn�t start out to use two, but added the birch board as I went along as a way of checking things. Two planes were used before it was all over, a LV low angle jack with a 38 degree iron (50 degree total) and a vintage Keen Kutter K4C with the stock iron. The LV LA jack was taking a shaving about 0.0015", the K4C a little less than that. Neither plane has been lapped though both perform well for me. I�m not among the habitual lapping crowd, and I�ve never lapped a plane unless I was having problems with it. Both of these planes worked well as received, even the vintage K4, so I didn't mess with them. Both irons were sharpened with a 8000 grit Norton waterstone.
I started by running the walnut piece over the power jointer. Since I don�t have a straightedge, I evaluated straightness initially by putting the stock jointed edge down on the outfeed table and put moderate (3-5 lbs?) pressure on the last six inches of the board. My thought was that this would accentuate any crown. Doing this, I could just barely encourage my thinnest feeler gauge, 0.0015", under the end of the very end of the board opposite where I was holding it, but it met increasing resistance almost immediately as I slid it toward the center of the board. If I put my hand in the middle of the board, I couldn�t really get the feeler under anywhere. Hard to know whether this means that the board was crowned or that the jointer bed had slight crown, which it certainly could from sagging under the cantilever.
At any rate, I later added the birch board to the experiment to see if comparing opposing faces and the associated doubling of error would help me. When I jointed both boards on the power jointer, then came together with no visible gaps with essentially no hand pressure. All this makes me think that my boards were starting within 0.001" of straight, although the scalloping from the jointer may obscure some deviations, by creating a more compressible surface.
The first plane used was the LV low angle jack. It took full length shavings on every pass and after 10 passes I put the board back on the jointer table. Putting my hand on the last 6" of one end, I could bring the 0.0015" feeler about 6 inches in from the other end. This seemed to be symmetrical.
To better check for crown, I rejointed the walnut then repeated the procedure with the LA jack using both the walnut and birch boards. When I brought them together before planing, there was no visible gap. After 10 passes on each (each board planed separately, not clamped together), I brought the jointed edges together and there was a visible gap at the ends. Naturally, this gap was accentuated when I held the boards together at one end only.
Having seen that someone else tried a smoother with this test, I did the same. Both boards were rejointed on the power jointer and fit without visible gap afterward. I then did ten passes with the K4C on both boards (again, separately). Perhaps significantly for this test, I noted that the shavings ran out at the far end of the board for about the first three passes, after which the remaining passes created full length shavings. This was not intentional, it�s just what the plane did in my hands, even though this did not happen with the LA jack. After 10 passes on both boards with the smoothing plane, the result was that the two boards fit together without a visible gap. I checked them on the jointer table as described before and wasn�t able to fully insert the 0.0015" feeler anywhere.
This result may be because the first couple shavings ran out leaving one end of the board high, counteracting any crowning that may have occurred later on. As I said, I didn�t intentionally do this; I don�t know if it is a �feature� of the plane or of my technique.
The next thing I did was to take these two, apparently flat edges, just as the smoother had left them, and take 10 passes on both boards with the LV LA jack. The result was pretty much what I had gotten the first time; this treatment appeared to create a slight crown in both that the smoother had not.
The final part of the test was a little weird. Having created an apparent crown with the LA jack, I took the crowned boards as they had been left by the jack, and took 10 passes on each with the K4C. A similar runout was observed in the first couple shavings, and after 10 passes, the boards fit together without a visible gap.
I�m not claiming my measurements are accurate, my planes are flat, my technique is good, or anything else � this is just what happened as best I can explain it. Guess the lesson learned is that I can pitch that LA Jack and the rest of my planes and just use that sweet little K4C as both smoother *and* jointer!
Your mileage will undoubtedly vary. . .
Dave
P.S. I broke my 0.0015" feeler trying to shove it under boards, so you owe me a new one. . .