"Arch" wrote in message
...
While facing a faceplate today I thought about how metal is milled and
wood is turned. In milling a rotating cutter is forced into sliding but
firmly held metal. In woodturning a sliding but firmly held tool edge is
forced into rotating wood.

Consider a horizontal milling machine doing what machinists term
peripheral milling and we term spindle turning. In climb or up milling
the work moves in the same direction that the cutter is revolving and is
forced toward the holding vise as it slides through the cutter. It
produces a smooth surface and wispy swarf. In the more conventional down
milling, the work is moved against the direction of the rotating cutter
and is forced away from the vise. This mode can produce a ridged surface
and chippy swarf if the work isn't held firmly.

Now consider scraping and shearing wood. In scraping the edge is moved
in the same direction as the revolving wood as the tool slides along the
rest. It can produce a smooth surface and delicate shavings. In
shearing, a tool edge is moved against the direction of the rotating
wood and if not controlled can produce a scalloped surface and distorted
shavings.


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.