I have written about my frustration with not being able to use planes on the douglas-fir slab because of all the tearout. Douglas-fir tears out fairly easily anyway and all the wild grain and knots just made things impossible, at least that's what I thought.
I had one more piece of the slab I used to make the dining room table, the only one with no knots, and I was determined to get to the bottom of this issue. I began by using the power hand plane to get the rough surface down to within about 1/16" of flat. I didn't use a scrub plane because the last time I tried it tore out something fierce, 1/8" in places.
What I tried first was taking a sharp #3 set to take very shallow cuts. I used it across and on both diagonals to the grain and it worked really well:
I also gingerly tried it with the grain but it started to tearout, so I stopped. I was still puzzled about why this has been so difficult. I have flattened my bench, which is cvg fir, with minimal tearout and successfully made other things out of fir.
I decided to do some research and essentially found what I have read previously except in a more extreme form. Several experts recommend setting the chipbreaker absolutely as close to the edge as you can possibly get it when planing difficult wood, literally a few thousandths. The reasoning is precisely that it breaks the chips before they can tearout, producing accordion like shavings and only a slightly rougher surface. Neither put emphasis on a tight mouth. One suggested a bevel-up plane with a blade sharpened at a very steep angle as an alternative, something I have. The blade becomes its own chipbreaker. Being risk averse, I decided to give both of these a try with the grain on the bottom of the slab. In both cases, I sharpened the blades carefully before beginning.
As you can see from this picture of the sidegrain, it isn't difficult to predict where it would tearout.
With the #3 freshly sharpened and the chipbreaker set as close as I could get it, I tried planing with the grain. Nothing happened. Taking the plane apart, I discovered why.
There wedged between the plane and the chipbreaker were the accordion shaped shavings. Not hard to figure this out. I purchased this plane a while back, sharpened it, tried it, and it worked fine, so that's all I did. Visual inspection of the front of the chipbreaker attached to the blade looked just fine, but it clearly wasn't when the chipbreaker was set this close. There was enough of a gap that the chips could force their way in. The fact that I use the ruler trick on my plane blades may have been a contributing factor, I don't know. After I cleaned up and shaped the chipbreaker, the plane started producing nice accordion shavings with no tearout, just a slight roughness in places. This is what the shavings looked like.
As you can see, they are somewhat short because they tend to break off. Next, I decided to try my Lee Valley bevel-up smoother with a 50 degree blade. In this case, the blade acts as its own chipbreaker because the angle of attack is 62 degrees. It too produced shavings without tearout, but they were distinctly different, not accordion-shaped and more continuous, leaving a surface that was slightly smoother.
The major difference between these two planes was that the bevel-up plane was noticeably harder to push.
That left the issue of why I had experienced such bad tearout with old #7. I removed the Hock blade and chipbreaker to look at them and this is what I saw:
The chipbreaker was set fully 1/16" back from the edge. Sharpening the blade and moving the chipbreaker up to the very edge of the blade gave me long continuous shavings with very slight tearout, easily removed with a cabinet scraper.
You can see what a tight roll the chipbreaker being set up like this produces. I think the reason it isn't accordion shaped is that the Hock chipbreaker is at a lower angle than the stock Stanley one. The front of it has the same shape as the blade and is about the same thickness. It's like a second blade turned over and with a slight bow in it.
What are the takeaways? First, I don't know why I have to continually relearn this lesson, but when something isn't going well it pays to stop and figure out why rather than just blundering ahead.
More significantly to readers of this blog who are hopefully not beset with this failing, the advice to set the chipbreaker absolutely as close to the edge as you can get it when planing difficult wood is confirmed. You don't want to do this normally, because the resulting accordion shavings are not continuous and leave a somewhat rougher finish.
Finally, I think Lee Valley's claim that the low angle smoother with a 50 degree blade will do a good job on difficult grain is also confirmed.