The procedure is not that difficult
if you are talking about laying out
the Lewis Y factor.  Everything must
be converted to a 1 Diametral Pitch
system.  A point perpedicular is drawn
at the tip to the vertical centerline
of the tooth.  From that point a line
is drawn to the tangent of the fillet
radius.  From that point a horizontal
line is drawn to the vertical centerline
of the tooth.  From the line tangent
to the fillet radius a perpedicular
line is drawn to intersect the vertical
centerline.  The vertical distance between
these two intersection is called the X
dimension and the Y factor is 2/3 times X.
It is hard to describe without using a
drawing.  But the Lewis Equation for gearing
is well known and there are calculations
or formulas to do this.  I feel that the
layout method is more reliable than making
a mistake in the calculations.  
I hope this makes sense.  AGMA should have
illustrations that depict this method for
load at the tip calculations.  Actually
the loading at the pitch line may make
more sense in this case and give you a
higher value.  In this method you
would draw a line tangent to the pitch
line to intersect the centerline of the tooth
and proceed as above to construct the other
lines and your Y factor would increase.
I am certain that someone has gone thru setting
up this procedure in an excell spread sheet
but I do not have it.  The European method
of using 30 degrees tangent to fillet radius
up to the center line. Then a perpendicular
line to the that line at the point where
it intersects the fillet radius down to the
centerline of the tooth should also give you
a close value and may be easier to layout.
The weakness in this method is that it assumes
a decent fillet radius and splines do not have
much of a fillet radius.

my God, DiamJim
have i found the most expert in gearing??!!
i'trying to follow your explanation (extremely cleary)
and 'll trying all the week i think.
thanks and have a good weekend!

Jim,
this is a spline, not a gear pair! therefore there is no one-tooth load on it.
Calculate the shear stress and the pressure between the two surfaces, take into account 50-75% of teeth in contact.
gearguru

Gearguru,
I know it is a spline but I assume the
load is not dynamic and the teeth will
deflect enough to allow almost full contact
around the circumference.  
You may be right in that my assumption
is false that all the teeth will be in
contact.  Thanks for looking at this.
I assume you would then agree that the
load at pitch point might be more reason
approach.  The only thing questionable
is that it does not account for thin
section parts i.e. that the internal
spline have enough section to take
the loads that would be imparted by the
30 degree pressure angle creating a
vectorial force outwardly.

The splines were always checked as I mentioned. The contact stress between the internal and external splines, and the shear stress. If you want to calculate it more "scientifically" then I recommend the new DIN standard (when I saw it last time it was still just a proposal; on Monday I can check the DIN standard number if you are interested).
But you can not apply the Lewis' method of bending stress to calculate it. The teeth are (theoretically-thats why I said take 50-75% of them) in full contact, therefore no bending, just contact stress and shear stress.
gearguru

i fell confused:
one of yours are in right or everyone .. becouse
there is a difference in your own therory.
when i calculate load consider bending stress?; but
only in case of spline and not in front of a gear pair ..
right?
and what about DIN standard?

The DIN 5480 is a dimensional standard, you'll find there all details about the profile, including the tolerances.
To calculate the stress in the spline teeth per DIN, you will need the E-DIN 5466; last time when I saw it (October 1997), it was still the E-DIN, which means it was not valid standard yet, just a proposal.
Sorry for the confusion, Reading/study these standards would help a lot, especially the 5480. Both of them are available in English version.
gearguru

thank you gearguru. so i will find E-DIN!
i hope that it is what i am looking for ..