diameter ratio for hollow shaft
diameter ratio for hollow shaft
(OP)
hello
In reading various design specs for hollow shafts (that will see torsion and rotating bending), I have come across the design guideline that ID / OD <= 0.65.
In fact I have several Navy specs that say "ID / OD must = .65" .
Going through my books, I cannot find a rationale for this.
Any guidance as to where this comes from would be appreciated.
thanks
magicme
In reading various design specs for hollow shafts (that will see torsion and rotating bending), I have come across the design guideline that ID / OD <= 0.65.
In fact I have several Navy specs that say "ID / OD must = .65" .
Going through my books, I cannot find a rationale for this.
Any guidance as to where this comes from would be appreciated.
thanks
magicme
not all that glitters is gold.





RE: diameter ratio for hollow shaft
Common sense tells me that the ratio is based on the notion that the outer diameter of a rotation shaft carries a larger portion of the torsional load while it decreases to nothing at the center of the shaft.
So, short of working a spread sheet out to determine the answer my best guess is that the .65 results from some value that states "that 80% of the load" is carried in that id/od range.
roadapple
RE: diameter ratio for hollow shaft
<tg>
RE: diameter ratio for hollow shaft
I recall years ago when working with press-fit shaft couplngs, the same .65 diameter ratio was used for the coupling hubs.
regards
magicme
not all that glitters is gold.
RE: diameter ratio for hollow shaft
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: diameter ratio for hollow shaft
I haven't found a definitive source for the 0.65 however
"The Mechanical Engineers Data Handbook" by James Carvill I
have found that Di/Do = k and on page 7 of this book. It lists various k values for hollow shafts and compares the
outer diameters, weight and angular deflection for a particular hollow shaft against that of a solid one ie:-
k 0.5 0.6 0.7
---------------------------
Do/Ds 1.02 1.047 1.095
Wh/Ws 0.783 0.702 0.613
Θh/Θs 0.979 0.955 0.913
the fomula's given are as follows:-
For a hollow shaft to have the same strength as an equivalent solid shaft:-
Do/Ds = (1/(1-k^4))^0.3
Wh/Ws = 1-k^2/((1-k^4))^0.3
Θh/Θs = ((1-k^4))^0.3
and finally k= Di/Do as previous
hope this helps
best regards
desertfox
RE: diameter ratio for hollow shaft
but I tried ratios of that tabulated data and can't find a reason to pick one value of k over another.
still hunting,
and of course the longer it takes, the more determined I am to find the rationale!
magicme
------------------------------------
"not all that glitters is gold"
RE: diameter ratio for hollow shaft
The only reason I can see to pick different values of "k" would be suit your particular critera ie:-
if weight was the main critera then you would perphaps use
a hollow shaft with a k=0.7 as this would only have 61.3%
of the weight of a solid shaft.
If you were restricted for space you might choose a k=0.5
to keep the diameters of a solid and hollow shaft fairly close.
regards
desertfox
RE: diameter ratio for hollow shaft
I find this equation interesting.
If we let the ID equal OD - 2t, then t=.175 OD
ie the wall thickness. I do not know where thin
section vs thick section columns is defined.
If so then the equation
ID / OD <= 0.65.
may make some sense.
Or t >= .175 OD
RE: diameter ratio for hollow shaft