[PSUBS-MAILIST] Gamma bow dome

Alan James via Personal_Submersibles personal_submersibles at psubs.org
Fri Feb 27 15:20:22 EST 2015


James,in your retaining ring photo, what are the four protrusions with holes in, on the inside of the ring for?Alan
      From: James Frankland via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Saturday, February 28, 2015 4:49 AM
 Subject: Re: [PSUBS-MAILIST] Gamma bow dome
   
It took me about 5 mins to do the drawing on MS paint! I think you mean something like Stachiw's book, page 524 fig 11.76.  Bottom drawing.  Probably will work just as well.  No machining required!


On 27 February 2015 at 15:35, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Thanks, you went to some trouble making that drawing, but it certainly added clarity. In my case the outside wall of the acrylic is completely square and there's virtually no gap at all between seat and window, its literally a few thousandths. I could machine the seat to take an O-ring groove, as you did with the retaining ring. However, PVHO 2-2.11.1 says "As primary seals for standard window geometries shown in Figs. 2-2.1 through 2-2.4, a soft elastomer compressed between the high pressure face of the window and retainer ring will be acceptable. The soft elastomeric seal may take the form of a flat gasket, or a seal ring with O, U, or X cross section." 
Given its so easy to cut out a circular flat gasket, I think I'll try that first and see how it goes. If there are nuisance leaks, I could upgrade to an O ring by machining the appropriate groove, but I'll try the lazy approach first. These bolt-on window seats are nice in that they allow for later modification. 

Best,
Alec


On Fri, Feb 27, 2015 at 9:56 AM, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Alec, The epdm gasket was really just to relieve stress on the seat of the dome.  This was with advice from the guy who built the Canary island subs who came to visit me.  Although of course it should provide sealing at higher pressure.   Emile made the dome and mounting ring and suggested I would need another seal for low pressure.  So, I made the low pressure seal an O ring sitting in a machined groove in the retaining ring.    See hastily drawn picture.   The gap where the O ring sits is nowhere near as severe as it looks in the picture, which is of course not to scale or anything.   I would love to say it was carefully engineered, but im afraid I just winged it a bit.  To start with the O ring groove was just a chamfer.  This didn't work as I couldn't get the O ring to stay in.  Then I machined it for a very small O ring.  Couldn't get it in.  Eventually, I got a groove and O ring combination that seemed to work.  There is lots of silicone grease on all surfaces as well.  It doesn't leak.  RegardsJames 
​  

​
On 27 February 2015 at 14:05, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi James,
That's some good looking hardware! Just a question if I may. Do you have just the gasket for making a seal, or is there an O-ring as well? 
My project sub has a bow dome seated in an aluminum ring. Currently the window is just sitting on a gasket with no O-ring, but I'm wondering whether to switch to an O ring. The window seat is 90 degrees square, so one possibility would be to chamfer the edge of the acrylic and put an O ring in the angle. That is what I did on Snoopy's hatch dome, it worked well and is a solution that doesn't require any changes to the seat. The other option is to put an O ring at the top of the acrylic and squeeze it with the retaining ring, but that would mean machining a chamfer into the seat, and would require machinery larger than what I have here. Or of course I could do nothing and see if it seals well with just an EPDM gasket.

Thanks,
Alec
On Fri, Feb 27, 2015 at 8:40 AM, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

​Hi Hank.   Yes, agreed, my dome does sit on a gasket.  The actual edge of the acrylic itself sits on a 1mm epdm gasket that sits onto the aluminium ring.  That ring bolts to the main reinforcing ring and has an o ring like you say.  Maybe this does give it a little bit of leeway. My dome is off at the moment, so I will have a look at the weekend and see if I can see any distortion on the reinforcing ring.  Im pretty sure there is none, or none that is detectable by the naked eye\straight ruler.  The alu ring seems to fis to it perfectly.   I suppose the best option is like you say, get it machined after welding.  You wont have to worry at all then. 
​   
On 27 February 2015 at 13:23, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:


James,
I am just assuming it needs to be perfect ? and I can not imagine that it will not warp at least a small amount.  I am not experienced with how such heavy material will react. Your dome sits on a gasket witch may give you some forgiveness. Maybe Emile can comment having done this also.
Hank--------------------------------------------
On Fri, 2/27/15, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] Gamma bow dome
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Friday, February 27, 2015, 7:28 AM

 Do
 you need to go to all that trouble?  When I did mine, the
 reinforcing ring was milled flat on the seating surface and
 I just pre-heated it and welded it in.  It was so big I
 don't think there was any distortion and it doesn't
 leak. Just thinking of saving you
 what sounds like an expensive job.
 On 27 February 2015 at
 11:45, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:
 James,

 I am amazed at the equipment some of the big shops have. A
 vertical mill is probably the way to go.  I am checking out
 another option also.  There are machines made to machine
 pipe flanges that clamp on and are portable.  There is a
 company in Calgary that specializes in this. I am just not
 sure yet what the accuracy is yet.  It is nice that I live
 only 3 hr from a big oil town that caters to the oil
 industry.  You can tell that oil is low, and the shops are
 slower.  I ordered the ring on a Friday and it was ready
 Monday.

 Hank    --------------------------------------------

 On Fri, 2/27/15, James Frankland via Personal_Submersibles
 <personal_submersibles at psubs.org>
 wrote:



  Subject: Re: [PSUBS-MAILIST] Gamma bow dome

  To: "Personal Submersibles General Discussion"
 <personal_submersibles at psubs.org>

  Received: Friday, February 27, 2015, 4:08 AM



  Hi hank,Sounds like

  it will be a good
 modification.  How are they going to

  machine the ring?  Some sort of vertical

  mill?RegardsJames



  On Friday, 27 February 2015, hank pronk via

  Personal_Submersibles <personal_submersibles at psubs.org>

  wrote:

  Today I

  officially took the plunge and removed the forward
 ballast

  tank to install my new bow dome.  After much agony I

  decided to make the change.  I am not enjoying the sub

  because the forward window arrangement is not ideal for

  lakes with marginal visibility.  I went to the big
 city

  yesterday and picked up the reinforcing ring and should
 have

  it fitted in a couple of days.  I am bringing in a
 pressure

  welder to weld the ring and then the sub is off to the
 big

  city to machine the ring.



  Hank



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