George Lendich wrote:

 Paul I have a lathe, but I think it's unnecessary and complex - my question
is, if the flat plate doesn't need it why would the bellhousing?
I was going to pocket the thick plate area anyway.
If we have a tube 1.6" high it has to be a minimum of .25" at the bottom
(allowing only, 2 degree taper) - that's an average of .2" thickness.

It is a better way of doing it and it will be stiffer.

Then you have the fillet at the bottom (inside and out ) then extra rib
area to mate to the raised ring.

BTW speaking of fillets do you have a pattern making supply house there in Australia?

I have some small wax fillets I can send you as I bought a 1000 years
supply by mistake. Send me your address and I will mail you a bunch.
http://www.freemansupply.com/FreemanWaxFilletsB.htm

These are real easy to apply. You will need a tool to apply them.
No sanding or other finishing required. You stick them on and you
are done. Freeman can ship over seas.

My calculations show the difference between .5 lbs for the tube and .6
lbsfor the flat raised area (1" wide and .5" thick) give the there would
be extra added to the ribs and associated fillets (this is using the minimum
calculations). There may be more considering a pattern is not perfect.

Given the extra work and extra complexity in the pattern, extra difficulty
in pouring extra depth to the thin walls,  extra difficulty machining (i.e.
holding it down), mate it's just not worth it !!

I've tried to design-out complexity and weight and I feel your wanting to
put more complexity in. I'm battling to keep the machining costs down now !!

George (down under)

If you are going to do it that way it is better to put the ribs on the inside.

It up to you George. You only have to do the pattern once. 
I am sure the foundry can cast it. 

BTW on the bolt flange you only need two ribs per bolt.  One on either side
of each bolt.

Paul Lamar
 
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