Musing about up milling, down milling, shearing and scraping.

Although I see a lot of it, anyone "forcing" an edge into rotating wood deserves what s/he gets in the way of dismounts, flying shavings, broken tools and maybe facial remodeling.

Scraping is more likely to cause those problems associated with forcing, and broad scraping angles pick up and sometimes tear out fiber - a material consideration the milling process doesn't have to worry about. One thing that puzzles me about scrapers is that the best scraping technique, had it been applied while using a gouge, would have made scraping unnecessary.

Shearing does not produce scalloped surfaces - chatter from an overextended or dull tool, or a poorly supported piece of work produces a scalloped surface.

"George" skrev i melding news:4204c1f3 snipped-for-privacy@newspeer2.tds.net...

overextended

Well said, George! I completely agree.

As a beginner I used my couple of scraping tools a lot, including some special Sorby-tool.

As I learn more about sharpening and the different uses of gouges I find that two bowlgouges and two oval chisels and a roughing iron is all I need for bowls and spindlework.

But I can see that the inside bottom of small boxes would be a challenge, if ever I tried one!

Bjarte

Nope. They make 90-degree gouges for that which work well. They're called hook or ring tools, and they allow you to pare the end grain of the box/goblet the same way you pare the end grain working off the edge of a bowl - with a shearing cut.

Thanks for responding, George. An orphaned musing is a terrible thing to lose. A differing opinion is a good thing, dogma isn't. I only meant to share and provoke other ways to think about the cuts we make. We won't change the world as we know it, but future generations of woodturners will be saved. :)

Semantics aside, we aren't far apart. I said, "... but firmly held tool edge...." and "....in shearing...,a tool edge _if not controlled_ can produce a scalloped surface...." (emphasis added)

I considered a scraper edge as trailing the rotating wood's surface and a shearing edge as opposing the rotating surface. This seemed to be somewhat analogous to up and down milling. To cut rotating wood, a tool must move toward and penetrate the wood's surface. The wood can come toward the tool but not to it. This motion requires some force, even if very little.

I'll suggest another possible analogy. Not as specific advice for good woodturning, just as a brief respite from Jet vs Delta.:) I know (ok, believe) from experience that cutting metal below center draws the bit inward and produces a rougher surface. Cutting metal above center pushes the bit outward and can avoid a rough interrupted cut.

If the analogy is partially valid, are there any useful parallels or opposites for turning wood? I realize that this tortuous analogy is only loose and general, since wood is cut and scraped with much more latitude and with different cutting tools.

Who will be the first to post that a little knowledge is a dangerous thing? :)

Turn to Safety, Arch Fortiter

"George" skrev i melding news:4204e4fc snipped-for-privacy@newspeer2.tds.net...

Ah, well, _now_ I can throw away my scrapers!-)

Bjarte

Throw them my way. The ones I have made out of old files are not strong enough to work at the depths I am getting to now. I need a "real" scraper, but I just spent all my disposable income on a new accordion! Ricky

>

Don't know how far. For my examples, I use wood cut across the grain.

I view the work as the most flexible part of the turning combination. Any tool presentation which applies more of a force outward - more or less perpendicular to the surface - rather than downward toward the bottom, where it cuts as the wood wishes to be cut, can cause chatter. This can be because of the angle of the tool, or because the turner "rides" the bevel into alternately harder/softer wood. If the turner is foolish enough to give leverage to the piece, tool flex can begin to affect the process as well.

What I consider the worst possible presentation is the one where force is radial - stuffing the edge of the tool into the rotating work at close to

90/90. This is the classic scraping presentation, where the two portions of grain are lifted and/or torn and the piece departs the holding device if a bit too thick a scrape is attempted. If a gouge edge, which is wedge-shaped, and therefore drawn into such a cut, enters at a scraping angle, it's called a catch.

To me cutting is what drops a shaving, scraping or stabbing what throw one, and Newton's third law applies. It is, of course, an elastic "collision," (Leo) with the piece deforming.

As to shearing, consider the gouge. I have to use slashes, though it is curved in length and in width. After the edge lifts the shaving to begin, the gouge is rotated so the bevel can rub at a shear angle ( \ ) if looking directly in toward bottom, and (\) to cut, if you could look through the piece from above. It then takes a shaving along its engaged length as the wood is transported past the edge. As we know from other woodworking, even a sharp edge benefits from shear. Plane end grain without shear, or try cutting straight ahead versus drawing a knife along the piece if you need to refresh your memory. Shear is the optimum presentation for cutting wood because it exerts the least force which might develop into chatter or "scalloping."

My bet is on compression of the material by the bit. Same as scraping.

Are you referring to spindles? There the work squirms up in wood cut below center, and is burnished down from above. It's that elastic collision again. The best spindle cut, as we know, is produced by a tool named by the angle at which its edge is presented - a skew.

Alexander Pope

Hi Rick

No, what you need is a tool rest that goes close in, so you do not have the overhang. How do you think I hollowed out bowls 8" deep 45 years ago, bowl gauges, ring tools, and etc., where not invented yet!

Yes I know the answer, I used to say that too, : "that was then this is now"

Have fun and take care, also, make music Leo Van Der Loo

Ricky Dietsch wrote:

A bit of exaggeration there. The ring / hook tools are older'n Arch!

Hi George

Ring tools older than Arch ?? Hey Arch is that right ??? Maybe you should have come and told me Anyway if one does not know of their existence, that's almost the same as not invented, kind of. Still I do assume you would agree with keeping your tool rest as close as possible in any case, as someone said here, don't give leverage away, or something to that extend.

Have fun and take care Leo Van Der Loo

George wrote: