Planing technique question

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Greetings, I'm flattening an old schoolteacher's desk with maple top for a workbench. My 4 & 5 plane irons are scary sharp. I set the bite to a gnat's whisker. Etc. I got nasty tearout in both directions on two boards in the top. I have read of using a smooth plane to "work around" twisty grain. (The bottom has tearout on the same two pieces, and mill marks from the factory's planer.)
How exactly do you handle this? Swoop down gradually so you don't leave landing and takeoff marks? Go straight along, but ease off the pressure? Change the angle of attack for an extremely acute slice?
My local library system doesn't have advanced plane books, and I don't recall the _Plane Basics_ (or something like that) book to have discussed this in detail.
Thanks
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Without seeing the wood grain, that would be my first try. Plane at a severe angle so you're not only taking paper thin shavings, but narrow as well.
If you only have to remove a paper thin amount, though, a scraper would be cleaner, I'd think.
djb
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On Mon, 02 Feb 2004 23:16:34 -0600, Dave Balderstone

This has the effect of lowering cutting angle.
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Not sure how. Increases the shear, certainly.
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I'm having trouble visualizing why that would be so. The angle of the blade to the wood surface stays the same regardless of the lateral rotation of the plane, doesn't it?
djb
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On Tue, 03 Feb 2004 17:55:07 -0600, Dave Balderstone

Ever ride a bike up a steep hill? When it got too hard you rode from side to side across the street. You effectively lowered the angle of the hill - you went farther to get the same altitude gain. Same general principle when you skew the plane.
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wrote:

I'm not sure I can perfectly explain it, but rotating the plane does change the effective cutting angle when you consider the direction of the plane movement. Take the extreme example of turning the plane 90 degrees but continuing to move it in the original direction; in this case there would be an effective angle of 0 - the edge of the blade would "slice" the wood like a knife without producing any shaving. Another explanation would be riding a bicycle up a hill but instead of going straight up the middle of the street you slowly move across the street as you go up. The hill doesn't change its pitch, but the bicycle "sees" an effectively shallower (but longer) hill.
Charles Lerner
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I understand the analogy, but don't see the physics. The cutting edge becomes longer when you skew the plane, but the angle of the edge to wood stays the same in my visualization.
It's not a big deal... Maybe I need to let the idea simmer for a while and try to grok it properly.
djb
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Dave Balderstone wrote:

Tearout happens when grain changes direction, as in figure. The result is what amounts to unsupported fibers showing up in the direction that you are planing. By skewing the blade you are directing some of the pressure sideways rather than all of it being forward, with the stroke. This results in more support for the fibers being sliced. You're right, the angle of the blade to the wood doesn't change. If you visualise the wood as being the ocean and the figure/fibers being the waves, the result is like tacking into the wind. Straight o you are trying to push into the waves and going nowhere, by attacking at an angle you ride across the waves/fibers and are able to go forward. VERY mixed metaphor, but I hope it helps. Dave in Fairfax
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And while that's simmering, here's another puzzle that occurred to me. We use low angle block planes because they give a smoother surface than a smooth plane. We use scrapers at a high angle, because they give a smoother surface than a smooth plane. Those yummy planes Knight makes have steeper angles for tougher grain. So, basically, any blade angle other than the default is better...What?
(scribble, scribble) An 11 degree block plane micro-bevelled to 30 deg touches the wood at 41 deg, back angle of 11. A 45 deg smooth plane with 30 deg m-b touches the wood at 45 deg with back angle of 15A scraper blade looks like it touches at <5 deg, with <<5 deg back angle.. Four degrees makes such a difference?
I've seen ads for a book on sharpening that goes into this. Time to hit the library...
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You are looking at it from the planes perspective. Don't do that. Look at it from the direction of travel. It will become clear.

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Doh!
Okay, I think I can see it now when I think about the path the shaving is taking up the blade. The path along the bevel becomes longer the more the plane is skewed, which does change the effective angle.
Thanks to both you and jev for helping me with this.
djb
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: I'm not sure I can perfectly explain it, but rotating the plane does : change the effective cutting angle when you consider the direction of : the plane movement.
On my web site - Planing Notes - What Happens When You Slew, are a couple of tables that indicate the actual effect with perhaps a salutary note about the amount needed to have significant effect.
Jeff G
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From the uninitiated ,isn't this what good belt sanders were invented for ??? mjh
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Actually, it's what scrapers were invented for. :-)
I think it was Mario Rodriguez who had an article in FWW a few years ago describing how he approaches planing various problematic woods. One example was a crotch figure where you have multiple grain reversals. He described going at it with short, semi-circular strokes so that you minimize going against the grain and impart a slicing action to the plane. He was even using a block plane in this particular case.
I was a bit skeptical about the idea of using a block plane like that until I was working with some crotch koa and really having a hard time with it. After trying all of my various "ultimate" smoothers, I grabbed my old #60-1/2 with a Hock iron. By using the plane as an extension of my thumb and index finger, I was able to approach it with a short arcing motion. It was just the ticket.
(FWIW, the koa was for a box top for an xmas gift for my mom. Pics are at:
http://www.swt.edu/~cv01/koa2.jpg and
http://www.swt.edu/~cv01/koa3.jpg )
Chuck Vance
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I'm guessing your desktop is glued up from smaller width boards. If that is the case, I'd guess the grain was flipped every other board to minimize warp as the wood moves. That's generally what good technique dictates when you glue up something like 6" boards into a wider, lets say 36" top.
So when you plane, you're hitting some grain the best way and other grain so it tears. And I'd guess this would happen no matter how small a bite you're taking.
Didn't the old carpenters use a longer, lets say 18-24 and maybe longer plane to "level" a top and then to smaller for smoothing. Once as smooth as plane would give, they moved on to scrapers.
Today there are belt sanders that used properly would do as good a job if you don't sit in one place too long and hollow out a section.
There's another option which is that if you could remove that top of the desk and a friend or local wood shop, maybe even school had a wide belt sander, you could get them to run it through for a few light passes and it would be level.
just my .02.
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My thoughts exactly, that's what belt sanders are for. It always amazes me why so much stuff was made out of curly maple . One question does remain and that is some on this group have recommended that the wood be damped to avoid tear out with mechanical planing ,does the same hold for handplaning....??? mjh
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Green/wet wood cuts cleaner. Expanded fibers are softer.
I bought a low-angle LN plane to take care of that nasty curl. Cuts well in any direction.
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For really horrible stuff I use a spitcoat of shellac. It helps to stiffen the wood fibers and IMHO, works better than dampening a board. But curly maple isn't usually all that hard to plane, IME. I get best results with a low-angle smoother.
Chuck Vance
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Can't afford (and don't want) a belt sander, recoiled at the rental cost. I am seriously considering the wood shop option. This desk came with the house, has deep holes along the front from drills, saws, and whatnot. It'll take some hefty passes, but still your point is well taken.
I know about the edge flipping. What makes these two pieces so annoying is that they tear-out in _either_ direction.
And yes, I have also seriously considered flipping the thing over, but the tear-out problem is there, too. I also make my own tack cloth...and I don't own a crowbar. You can use a dollar bill for fine polishing, and when it wears out you can take it to the bank and they'll give you a new one!
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