Alan,
I don't know if that is still the case. I based my conclusion --
which is the same as yours -- on the early version.
It's not a bad approximation. True, it ignores the fact that the
shaft is more flexible closer to the tip. But the flexibility
measured by an F-meter or NF-4 is a weighted average over the beam
length, with most of the weight applied fairly close to the clamp.
Tom, any more up-to-date info?
And for those of you who just glazed over on "weighted average" -- or
Alan's description of the original formula -- don't forget that Alan
and I are engineers talking engineering. Really no other way to
discuss the subject without good graphics and a lot more words.
Cheers!
DaveT
At 08:22 PM 6/4/2009, Alan Brooks wrote:
Dave or Tom,
Last time I saw that formula it was a simple conversion from
frequency to EI product assuming a uniform rod of the unclamped
length that the frequency was taken at. Is that still the case? If
not, could one of you send me the current version?
Thanks,
Alan Brooks
At 12:26 PM 6/4/2009 -0400, you wrote:
At 11:49 AM 6/4/2009, Tom Wishon wrote:
When Tom Mace left the industry to go back to the academic world
at Cal Poly SLO, I had him do a complete full out EI of multiples
of all my shaft designs and flexes so I would be able to compare
the EI curves to see their relationship to our Bend Profile
software's progressive beam length frequency graphs. While the
shape and orientation of the EI curves were different, in relation
to each other by each different shaft, they were the same as what
we output in our bend profile measurement work. I've always
agreed that our BP measurements were NOT actual stiffness
measurement, but with this correlation check to EI, I am satisfied
they are valid for shaft to shaft comparison of relative stiffness
differences in shafts.
Thanks for that, Tom.
From what I can tell from the Bend Profile software, I think I
understand the formula used to go from your profile measurements
to EI profiles. It is a very simplified formula, much simpler than
Brillouette's work, but it may well be close enough for practical purposes.
One of the things on my to-do list is a comparison of the
simplified formula and the Brillouette formula, using some profiles
I have measured for the a variety of shafts. I have in my basement
"lab" a frequency profiler, an NF-4 deflection profiler, and an EI
machine. At least part of my motivation for this is to reclaim the
space now used by the EI machine. If I have a reliable and accurate
way to get an EI profile from other measurements (like frequency or
NF-4), then I don't need the EI machine any more.
Somehow, that project never seems to pop to the top priority. When
you're retired, on a nice day the top priority tends to be playing golf.
:-)
Cheers!
DaveT
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