Mark Barabas writes,
“I understand that a finished cut, or one that needs no additional work prior to finishing, can come from an edge tool, like a drawknife, plane, or spokeshave. I don’t understand why a scraper doesn’t produce a finished cut, and requires sanding prior to finishing. Can you explain this please?”
I would love to. This is a topic that I don’t … it’s been addressed a number of times, but a lot of people aren’t really understanding the scraper versus planing idea, and part of the problem is that it’s talked about, and this is a good example. Actually, you don’t say scraping versus planing; you talk about a scraper versus a plane. But it’s tools that are put, in some ways, in two different worlds as if one is doing something different to the wood than the other. And generally, it is. And the difference is generally very clear.
But in looking at tools that you … if you’re making your own tools … and I think, in the example of a bevel up low-angle block plane, the options for cutting geometry are almost unlimited, such that you can go from a planing angle, all the way up into a scraping angle, and past that, and play with that geometry, and watch what happens as you increase your cutting angle.
The reason that the scraper, as a tool, and I think you’re probably talking about a card scraper, is a card scraper is usually used…. Imagine this is a card scraper. I’m leaning the tool forward and scraping in. And in doing that, the tool is pushing down on the wood. And the scraper edge is a very fine line, so I’m putting a lot of pressure on the wood, at the cutting point. And what’s happening, in doing that, is with that negative angle, and that downward pressure that the scraper is putting onto the wood, everywhere that a pore emerges through the surface of the wood, it’s like a straw. And where it emerges, through the surface of the wood, the top edge of that pore, or straw, is super, super delicate. And there’s nothing underneath that delicate edge, to support it against the downward pressure of a scraper cutting.
So what happens is, where that unsupported wood is, is it just falls into the pore. And as you go by with a scraper, it can pop back up. That’s called raised grain. Sanding does the same thing; because it also cuts with a negative angle. It’s got these little rocks glued to the paper that have a negative cutting angle, and the harder you push onto the wood to get faster cutting with the paper, the grit, the more you’re gonna push that fiber into the pore, instead of cutting it off. Now a lighter touch with a scraper will help this. You could also use scraper planes, and tune them up, or there’s an article I did years ago, in Fine Woodworking, describing how to convert a low angle block plane to a scraper, and you can play around with the geometry there until you get that perfect control you need, without overly turning that edge over, or overly turning the chip over to press too hard against the wood, so that you force the wood down into the pores, where it’s open.
But the primary difference is the downward pressure. The overcompensation of a scraper, overcompensating the lift of a knife or a plane by pushing too hard down. There’s some balance in there, between lift and down, that you get a perfectly controlled cut, with no tear out, and no need to sand afterward. So if that didn’t answer your question, let me know, and we’ll try again another time.
–Transcribed as spoken