[PSUBS-MAILIST] Heads Question

[james cottrell via Personal_Submersibles]

I drew and asked.

      From: Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org>
 To: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> 
 Sent: Saturday, September 16, 2017 2:34 PM
 Subject: Re: [PSUBS-MAILIST] Heads Question
   
 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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