[PSUBS-MAILIST] heads

[Sean T. Stevenson via Personal_Submersibles]

EE could also do the machining for you. Probably expensive, but maybe cheaper than building a rotary table mill for 36"? You should only need to remove material on the outside.

Sean


On June 30, 2017 4:38:20 PM PDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Sean,I am getting clarification on where the sphericity is out of
>whack.  I assume at the equator.  I can machine them down myself, and
>rather that then trying to weld 3 inch material.  The heads start out
>at 3.5 inches to produce a minimum of 3 inches at the apex.Hank 
>
>On Friday, June 30, 2017 5:11 PM, Sean T. Stevenson via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
>
>I presume that the achievable diametral tolerance is a result of the
>head thinning at the apex during hot pressing / spinning as material is
>pushed towards the flange. I forget the numbers now, but some time ago
>I posted a synopsis sourced from someone at EE explaining exactly what
>the typical thinning was. In any case, full hemispheres exhibit more
>thinning than 2:1 SE heads or dished heads of lesser depth, just
>because they are deeper. Two solutions to this are to form thicker than
>you need and then machine to remove the extraneous material away from
>the apex (expensive), or to form multiple spherically dished heads of
>shallower form and weld them together to fabricate your sphere. Nuytco
>uses six such dished heads on the DeepWorker spheres, pressed once on
>center and then a few times around the outside to get the best
>sphericity of the dish before trimming to shape and welding together in
>a jig to create the sphere. This corresponds t! o acubic face
>construction, but you can do this with with as few as four sections,
>corresponding to faces on a tetrahedron, or as many as twenty sections,
>corresponding to faces on an icosahedron.Machining two hemispheres down
>to the apex thickness all over would give you the most theoretically
>perfect hull, but it is ridiculously expensive to do. Phil's method is
>a good tradeoff, at the expense of three times the welding.Sean
>
>
>On June 30, 2017 2:59:26 PM PDT, hank pronk via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>Hi Sean,I just heard back from EE with a cost for two 36 inch id  3.5
>inch heads, and they can not do 1% Diameter sphericity.  They can do
>ASME code witch is 1.25% or 5\8 inch.  I suppose that would mean
>machining the heads.  The heads could be machined to a very close
>tolerance then.  I would have to build a turret lathe then.Hank
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