On Fri, 30 Sep 2011 13:07:59 -0500, Arch wrote
(in message ):



Just musing,


I'm too lazy (read have forgotten how) to bother doing the math, but I
wonder how many linear feet of wood a burr scrapes per sec. when it
touches a bowl turning at any reasonable rpm. I doubt a fragile hooked
burr lasts long on a wood-turning scraper, but there's no doubt that a
burr seems to work for a period longer than expected. I wonder if the
effects of a burr that last any time at all are really due to improving
the edge and not the burr.


snipped the other part of Arch's query


Turn to Safety, Arch
Fortiter


http://community.webtv.net/almcc/MacsMusings




Let's see, now. We're dealing with a round thing, so that means we have to
use pi and either a radius or a diameter. I always struggle with the choice,
radius or diameter, so I get a little silly. One possible formula is Area
equals pi R squared. (Or is it Area equals pi D squared?)Then I say to
myself, "but that is silly, as everyone knows pie are round." In my world,
then, I know the formula is correct, A=pi x R squared.

That means for me, then, that circumference is pi times Diameter, and now my
dimensional choices are sorted out, and I can continue.

Surface speed will be an expression of the number of circumferences that pass
by the tool rest in a second. Consider then a spindle 4 inches in diameter,
turning at 300 RPM. In one second that spindle makes five turns (300 divided
by 60). The circumference of a 4 inch diameter spindle is 12.56 inches (3.14
times 4). It is too bad that a key number for round objects is not a round
number, itself. It makes things messy.

I digress.

At a rate of five circumferences per second, that means then, that the
surface of the spindle is moving at 62.8 inches per second, or just a tad
over five feet per second.

I'm a fairly sturdy guy, and can push a cabinet scraper with gusto, but I can
not scrape a five foot board in one second. Depending on the species of wood
I am scraping, and how much effort I am putting into that scraper, I might
have to re-do the edge of the scraper a couple of times before I am done, and
I am moving much slower than 5 feet per second. I am afraid that a hook edge
scraper tool on a lathe will not have a long life before needing a re-do.

One of the advantages of a cabinet scraper in "flat" woodworking is its
relatively broad area compared to a smoothing plane, for a final surface. In
wood turning, the contact edge of a hook scraper will be short, and I think
there is a likelihood of an uneven surface - a bunch of very fine and very
smooth grooves, side-by-side.

Respectfully submitted for your consideration,
tom koehler

--
I will find a way or make one.