[PSUBS-MAILIST] Heads Question

[Sean T. Stevenson via Personal_Submersibles]

Don't ask.  Draw.  Create a proper manufacturing drawing with the
material and all of the required tolerances indicated.  Use GD&T where
applicable.  Roundness, sphericity, etc. all specified on the drawing. 
When you make a request for quote, it's as simple as "one part
manufactured per supplied drawing # nnnnnn".  They quote against the
drawing, and if they make a part that doesn't match the drawing, you
don't pay for it.  Simple.

Sean


On 2017-09-16 11:14, hank pronk via Personal_Submersibles wrote:
> Greg,
> The problem with calling it a vacuum tank is the sphericity.  ASME is
> not as fussy as ABS for sphericity, and if you ask for the proper
> sphericity the cat is out of the bag.  
> Hank
>
> On Saturday, September 16, 2017, 10:50:57 AM MDT, james cottrell via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> Hi David,
>
> In my experience it was cheaper and faster to hire an ASME tank
> fabricator to produce a steel cylinder with the head (or heads) welded
> on. Mine came machine welded with an ASME code stamp. 
> If your design will feature external frames, ask them for both heads
> welded on. If your design will feature internal frames (done later)
> ask them to weld one end only. This will be cheaper in the long run
> and better built. It's hard to beat pressure vessel code machine
> welding. Specify NO backing strips.
>
> Another tip- call it a "vacuum tank".
>
> Greg Cottrell

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