Doug Dawson wrote:
~ It's been a slow day on the oldtools list, so I had to fill out
~ my dinner break with _something_... :-)
~
~ So far we have a concrete estimate by the ISO of acceptable standards
~ for plane sole flatness. As far as I know, the derivation of that
~ standard did not take into account sole flexure, i.e. bending of the
~ sole of the plane under downward pressure applied to the plane,
~ through the tote, while planing.
Now this is something new! Standards as estimates. How does one have a
concrete estimate? 8-).
~ It's not hard to get a reasonable idea of what effect that would
~ have, for a cast iron bench plane, using standard structural
~ analysis foo. The exact analysis allowing for precise shape and
~ so forth is tedious, but we can get a reasonable ballpark figure.
What is a "Ballpark" please? - somewhere where this strange American
game of rounders is played perhaps, (the game being strange of course,
never the Americans, never, oh dear me, never!) and what have figures
got to do with it? Do they never know the exact score or something?
8-).
.
~ Now consider our Stanley #8, for which we have the following data:
~ Plugging in that data, we arrive at:
~
~ d(sole) = ( 7.9x10-3 W ) inches, or 7.9W thou.
~ d(sides) = ( 2.5x10-3 W ) inches, or 2.5W thou.
~ Remember that W is numerically equal to the downwards force in
~ pounds, applied to the plane in use, i.e. whenever this _matters_
~ for want of a better way of putting it.
~ The sole and sides operate in unison, rather than independently,
~ of course, so I'd tend to think we can safely estimate the total
~ sole flexure at around 2W thou
~ So, we'd be led to believe that a downwards force of 10 pounds
~ during planing, not totally unrealistic, would result in a
~ downwards mouth deflection of around 20 thou, or around 1/64 inch.
Messing about, plane in hand, with bathroom scales on the bench top
(to examine another theory), I found that with my puny 11 stone (154
pounds) I can register about 90 lbs on the scale. According to Doug's
figures, this makes a deflection of about 180thou or 0.18 inches. Cor
blimey! Cor luv a duck!
Perhaps we should take off our hats, (or maybe some other garment?) to
Doug for so nobly sacrificing his dinner break for our enlightenment.
~ Make of this what you will.
Done that Doug! 8-).
~ .......................... It always has to be taken into
~ account in considerations of sole flatness and its significance.
Of course we should pay tribute to this static analysis. What I wonder
would be the outcome of an analysis of the dynamic situation, taking
into account of the need progressively to adjust (no split infinitives
here, no siree) for temperature rises. To what extent does suction on
non-corrugated soles affect this deflection, one gently enquires?
~ ....... counteracting the natural concavity of the sole, and
~ flexure there will be _significantly_ less, much less so than
~ the above numbers and formulas would indicate, methinks.
However, from where does the ISO's Chief Savant derive this concept of
/natural/ concavity (undefined in extent) of a plane sole? Observation
and testing of a statistically significant quantity? Workshop lore?
Exchange of data at one of these swapmeets one reads about? Mind you,
most of us from time to time can get preoccupied with certain
concavities, and convexities for that matter, especially when
well-dined on a Sunday evening.
Perhaps next time Doug is well-dined, he might favour us with his
formula for natural concavity, no doubt including factors such as age,
(the plane not the owner!) nature, location and area of patent marks,
length, presence of a complete decal (whatever that is), whether it
has a low or high knob, factors for rosewood and otherwise, japanning
percentage, whether bedrock or not and so on. Minor factors such as
mis-match of knob and tote patterns can perhaps indulgently be
excused.
Jeff
--
Jeff Gorman - West Yorkshire
jeff@m...
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