[PSUBS-MAILIST] heads

Sat Jul 1 15:09:17 EDT 2017

Okay,I stand corrected, a 36 inch sphere is too small.  I just spent some time in my escape pod and it might get uncomfortable.  I think 40 inches ID would be perfect.Hank 

    On Saturday, July 1, 2017 5:21 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Sean,Yes they offered to do the machining, and yes it would cost a lot, more than the heads. I am playing around with different size scenarios, starting with the absolute minimum size witch is 36 inches ID, the same as my escape pod.  Surprisingly it is spacious enough and quite comfortable.  I would have to do a mock up to be sure all the bits and pieces fit in.  The benefit of coarse is the weight drops by around  3,000 lbs.  That makes a giant difference in cost of foam.Hank 

    On Friday, June 30, 2017 10:34 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 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 

    OnFriday, 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 oncenter 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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