> Doug D. wrote:
>
> (snipping much good analysis of what's going on with flexure...)
>
> I really hesitate to get out out of my quiet, comfortable spot in the
> corner next to the cracker barrel. I've been there stuffing my mouth
> full of crackers to prevent any more too-quick comments.
>
> But, Doug, phtooie, phtooie!....(oops, sorry, I'll clean it up that
> mess in a minute...oh, are those your good pants?)

   S'okay, their only my work skins.

> >   It's been a slow day on the oldtools list, so I had to fill out my
> >   dinner break with _something_... :-)
> Must have been an extraordinarily tiring one.
>
> I really don't want to rekindle any long smouldering differences
> between theorists at their desks and engineers who have to actually
> face the "real world", so don't take this wrong. For the sake of those
> who might have copied your plane sole deflection calculations onto the
> front of the refrigerator, I gotta say, I think you missed (due to
> fatigue) some important things that really mess up the results.
>
> #1 - The interaction between the sides of the plane casting and the
> #sole are
> totally different than the way your math treats them, since they are
> actually one piece.

   Absolutely right, this has to be taken into account. OTOH, if you
   look at the relative figures, the sides are dominant in resisting
   flexure, the sole is only a perturbation on that.

> #2 - I know that for the sake of the KIS principle you didn't deal
> #with the
> fact that the side thickness isn't XX" as you said, and is tapered -
> joined to the sole with a rather large radius...Well, that alone
> throws the calculation way off. But not as much as #1.

   OOPS!!! _Most_ excellent point. It approaches 3/16" at the base. That
   increases the effective side height even further, even moreso at the
   centre hump ( - see my reply to Paul. )

> #3 - My Phtooie alarm went off as soon as I read:
> >   The Young's modulus, or modulus of elasticity, of cast iron, is: E
> >   = 152.3 GPa = 22.1x10^6 psi
> Among REAL WORLD practical people, it has become pretty standard to
> apply a FF (Fudge Factor) to anything that comes from theoretical
> physics.

   That came from an engineering handbook. I'm not really sure what the
   tolerances were, because they didn't quote them. ( *$%(@&^(*
   engineers, I've lost track of the number of courses in experimental
   statistics I've taught them, and they just never learn the stuff,
   it's not in their nature. :-( Pretty typical - I hope they learn THAT
   in the real world, cuz they refuse to learn it here. ;-) )

> To be more constructive - A factor your formula needs is something I
> picked up at a public library several years ago out of a 40 year old
> book. It's a table of factors to be used as divisors when using
> Young's modulus here on the surface of this REAL world, where I spend
> most of MY time.
>
> Reginold T. Smith (of Austrailia somewhere) created a fudge factor
> table to deal with the discrepancies I'm talking about. (He even
> labeled the "units" REGS - must have been an ego thing)

   I'd be interested in that. Prolly too specialized to post publicly
   though, unless someone protests. I don't have any resources of that
   sort, and wouldn't have a clear idea of where to look for them, aside
   from generalities.

> Well, I had copied it down, and had played with it before, so I dug it
> up now, just to check out your theoretical results. Because they just
> didn't sound quite right to me.
>
> The revised (your) formula for a piece 24" long says 10lbs. at the
> mouth can deflect the surface .003. Kind of a long way from what you
> suggested I think.

   I'd have to verify the circumstances, doctrine, etc., because in
   something truly quantitative like this you have to watch exactly what
   procedure is being used.

> So (since I don't have cable TV) I checked it out on a #8. Sure
> enough! (although admittedly I got .004" with 10 lbs.)

   Again, precise layout? As noted in my response to Paul, it really
   makes a big difference to the outcome.

> But, going back to specific refinements needed for your formula -
>
> #5 - I calculate that the force directly downward on the knob and
> #tote to
> produce 10 lbs at the mouth at 18.6 lbs. Ignoring the problem of doing
> that with the shape of the tote, what it would take to deflect it
> .020" would leave my feet off the floor. How am I going to give it a
> push forward?

   I was meaning to comment on this in a reply to someone else. With the
   #8, in particular _my_ #8, which looks like any other so I feel
   pretty safe here, pressure applied to the tote during planing would
   present a downwards force virtually equidistant from both ends. And
   that's only the vector component directly into the wood. I said it
   was not totally unrealistic, playing the optimist, but I'll leave it
   to others to comment more carefully on just to what extent that's
   true. I envy the other people who have the measuring equipment to be
   able to determine that, I don't have the stuff. Wish I did.

> I'll reprint Mr. Smith's conversion table I suppose, for anyone really
> interested. But it's even longer than this post.
>
> Long note just to say "Back to the drawing board, Doug." And I hope
> this week isn't as exhausting for you. :^)

   Thanks for the point on the tapered sides. Now Paul's measurement is
   completely consistent with my prediction, at least insofar as what I
   did was meant, as stated, to be a ballpark estimate of how much
   deflection you could likely never _exceed_ reasonably, to well within
   an order of magnitude. All the above said, our results seem to be
   fairly close.

   Again, just a back-of-the-envelope calculation to suggest an extremum
   of possible deflections. You'd really have to do a more elaborate
   analysis, methinks, to improve on it.

   More later.

   Doug Dawson dawson@p...