- Joined
- Apr 21, 2015
- Messages
- 653
I have a confession to make.
This is hard to admit. (Heavy sigh)
I ... I'm ... I'm a reformed woodworker. There! I've said it.
I'm in the middle of an absurdly long thread about making a set of straightedges. It's basically a public diary of my monomaniacal pursuit of metal scraping. I'm hopeful that readers of this diary think me slightly less insane than my family and friends, but if not, so be it.
Anyway, ....
The more I worked at scraping in these straightedges, the more vaguely familiar the whole process seemed. Eventually it hit me (and I've never seen mention of this anywhere):
Metal scraping is almost the exact equivalent of using hand planes and spokeshaves in woodworking. To more of a degree than might at first be apparent.
Bear with me here. This was by far the biggest epiphany I've had since I first tried my hand at metal scraping.
Not many people other than crazy handtool enthusiasts like myself attempt to dimension lumber by hand any more, but those that do should be familiar with something called a scrub plane. It's the very first plane you use to to make a roughsawn surface flat and smooth. Unlike the larger, wider, longer, flatter planes you use later in the process, the blade is fairly narrow. The end of the blade also has a very pronounced radius (about the curvature of a quarter or maybe a half dollar), it has a fairly short base, and it's used with a wide open throat.
A scrub plane removes a lot of wood quite quickly. It takes deep bites and produces very thick shavings. You use it to knock down major high spots to remove any twist, cupping, or bow. The resulting surface may be relatively flat (all the high points in the same plane) but it will have a very pronounced ripple.
Furthermore (toot doodle doo!) you push a scrub plane along a line at 45 degrees to the board you're flattening. First in one direction, then 90 degrees in the opposite direction. EXACTLY like metal scraping.
Check out this video of a scrub plane in use, starting at about 2'56" -- the process and resulting surface should be very familiar!
Once you've "flattened" a board with a scrub plane, you start removing the cross-hatched ridges it leaves behind using planes that have progressively wider blades and progressively less curved cutting edges.
Sound familiar?
This epiphany suddenly clarified something that I'd completely misunderstood from Richard King's scraping class.
I've no doubt that this is spelled out clearly in the handout from the class that I've somehow managed to misplace (I'm no longer capable of hanging onto physical printouts, apparently). But the process of metal scraping should proceed from fairly narrow blades with a very tight radius for roughing, to a quite wide blade with a very large, gentle radius (and light touch) for finishing.
I'm embarrassed to admit that I had this all mixed up. I thought you roughed with wide blades, then used narrow blades to pinpoint and finish.
I "finished" one of my straightedges to a very high degree of flatness using a fairly narrow blade and far too pronounced a radius.
My epiphany occurred when I temporarily quit working on reference gages, and started scraping in the top (non-bearing) side of my lathe cross-slide for a break. This wasn't a critical surface, so I wasn't pinpointing or trying for more than 20 PPI or so.
Here's a photo partway through the process:
(If you look closely, you can see a pretty substantial hole just above the circular slot for the compound).
I used a much, much wider blade with a slightly wider radius for this surface than I last used for the straightedge. I was amazed (and, frankly, disheartened) to discover by touch that this surface was considerably smoother than that of the straightedge, even though I was absolutely certain (by spotting on the surface plate) that the straightedge was flatter with more PPI.
(I was disheartened to realize that I still need to put several more scraping cycles into my straightedge).
Put simply, and it seems obvious now, you should start roughing by creating fairly narrow and deep gouges with a narrow, tightly curved blade, then finish with quite gentle and shallow shavings using a wide blade with a very gentle radius.
I think I was also making a pretty major mistake by bump scraping with far too much pressure, creating much deeper scrapes than are called for in final finishing (if narrow and short as they should be).
One last point regarding the plane analogy: like a wood plane, the scraper does not take off uniformly thick shavings. You can actually feel this as you "snick" through a high point. That's the whole point: the edge of the blade should follow a relatively continuous "scoop" regardless of intervening bumps and troughs. You start cutting a shaving before a blued up high point, then snick through it. Your hands and ears will actually feel and hear a slight "tick" as you hit this increased resistance.
I hope this is useful to someone else. This honestly feels like a huge breakthrough in understanding for me, after literally a couple months of scraping.
Regards,
--
Rex
This is hard to admit. (Heavy sigh)
I ... I'm ... I'm a reformed woodworker. There! I've said it.
I'm in the middle of an absurdly long thread about making a set of straightedges. It's basically a public diary of my monomaniacal pursuit of metal scraping. I'm hopeful that readers of this diary think me slightly less insane than my family and friends, but if not, so be it.
Anyway, ....
The more I worked at scraping in these straightedges, the more vaguely familiar the whole process seemed. Eventually it hit me (and I've never seen mention of this anywhere):
Metal scraping is almost the exact equivalent of using hand planes and spokeshaves in woodworking. To more of a degree than might at first be apparent.
Bear with me here. This was by far the biggest epiphany I've had since I first tried my hand at metal scraping.
Not many people other than crazy handtool enthusiasts like myself attempt to dimension lumber by hand any more, but those that do should be familiar with something called a scrub plane. It's the very first plane you use to to make a roughsawn surface flat and smooth. Unlike the larger, wider, longer, flatter planes you use later in the process, the blade is fairly narrow. The end of the blade also has a very pronounced radius (about the curvature of a quarter or maybe a half dollar), it has a fairly short base, and it's used with a wide open throat.
A scrub plane removes a lot of wood quite quickly. It takes deep bites and produces very thick shavings. You use it to knock down major high spots to remove any twist, cupping, or bow. The resulting surface may be relatively flat (all the high points in the same plane) but it will have a very pronounced ripple.
Furthermore (toot doodle doo!) you push a scrub plane along a line at 45 degrees to the board you're flattening. First in one direction, then 90 degrees in the opposite direction. EXACTLY like metal scraping.
Check out this video of a scrub plane in use, starting at about 2'56" -- the process and resulting surface should be very familiar!
Once you've "flattened" a board with a scrub plane, you start removing the cross-hatched ridges it leaves behind using planes that have progressively wider blades and progressively less curved cutting edges.
Sound familiar?
This epiphany suddenly clarified something that I'd completely misunderstood from Richard King's scraping class.
I've no doubt that this is spelled out clearly in the handout from the class that I've somehow managed to misplace (I'm no longer capable of hanging onto physical printouts, apparently). But the process of metal scraping should proceed from fairly narrow blades with a very tight radius for roughing, to a quite wide blade with a very large, gentle radius (and light touch) for finishing.
I'm embarrassed to admit that I had this all mixed up. I thought you roughed with wide blades, then used narrow blades to pinpoint and finish.
I "finished" one of my straightedges to a very high degree of flatness using a fairly narrow blade and far too pronounced a radius.
My epiphany occurred when I temporarily quit working on reference gages, and started scraping in the top (non-bearing) side of my lathe cross-slide for a break. This wasn't a critical surface, so I wasn't pinpointing or trying for more than 20 PPI or so.
Here's a photo partway through the process:
(If you look closely, you can see a pretty substantial hole just above the circular slot for the compound).
I used a much, much wider blade with a slightly wider radius for this surface than I last used for the straightedge. I was amazed (and, frankly, disheartened) to discover by touch that this surface was considerably smoother than that of the straightedge, even though I was absolutely certain (by spotting on the surface plate) that the straightedge was flatter with more PPI.
(I was disheartened to realize that I still need to put several more scraping cycles into my straightedge).
Put simply, and it seems obvious now, you should start roughing by creating fairly narrow and deep gouges with a narrow, tightly curved blade, then finish with quite gentle and shallow shavings using a wide blade with a very gentle radius.
I think I was also making a pretty major mistake by bump scraping with far too much pressure, creating much deeper scrapes than are called for in final finishing (if narrow and short as they should be).
One last point regarding the plane analogy: like a wood plane, the scraper does not take off uniformly thick shavings. You can actually feel this as you "snick" through a high point. That's the whole point: the edge of the blade should follow a relatively continuous "scoop" regardless of intervening bumps and troughs. You start cutting a shaving before a blued up high point, then snick through it. Your hands and ears will actually feel and hear a slight "tick" as you hit this increased resistance.
I hope this is useful to someone else. This honestly feels like a huge breakthrough in understanding for me, after literally a couple months of scraping.
Regards,
--
Rex
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