[PSUBS-MAILIST] calculation

Tue Jul 7 08:26:39 EDT 2015

Alan,
When my dome made the mystery noise, I was at 100 feet deep. That puts about 18 tons on the dome.  I think it was either the straps were able to relax and find their happy place, or, the super cold water made the dome contract.
Hank--------------------------------------------
On Mon, 7/6/15, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] calculation
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Monday, July 6, 2015, 9:00 PM

 Hank,I was
 looking at some Deep Worker photos. The dome retaining
 bandslook like
 they can be wound tight from a central point at the
 top.I am
 wondering if they pre stress these significantly so that
 there is less movementwhen they
 are compressed at depth. 
 Also I
 commented on your retaining system when I first saw it, that
 I thought thevertical
 floatational force might move it upward, or the dome pivot
 out from the bottom.Perhaps
 you could exert more pressure on the dome with your clamping
 system?
 Alan

  From: Alec Smyth via
 Personal_Submersibles
 <personal_submersibles at psubs.org>

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

 Sent: Tuesday,
 July 7, 2015 12:31 PM
  Subject: Re:
 [PSUBS-MAILIST] calculation

 Does the
 window seat have some sort of inside diameter edge? I would
 think if it does not, then its pretty much guaranteed to
 slip with or without grease - with grease being the quieter
 less-terrifying option.
 Best,
 Alec

 On Mon,
 Jul 6, 2015 at 6:50 PM, hank pronk via Personal_Submersibles
 <personal_submersibles at psubs.org>
 wrote:

 Sean,

 Thank you for the input, I think I will just use weights
 like Alan says.

 I am making a fixture to simulate the EPDM gasket compressed
 under my dome.  I want to test it with grease and
 without.  I will squeeze the gasket in the fixture then
 push the top plate sideways with a pusher bolt to see if the
 gasket allows movement.  I want to make sure my dome can
 expand and contract at depth.

 Hank

 --------------------------------------------

 On Mon, 7/6/15, Sean T. Stevenson via Personal_Submersibles
 <personal_submersibles at psubs.org>
 wrote:

  Subject: Re: [PSUBS-MAILIST] calculation

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

  Received: Monday, July 6, 2015, 9:08 AM

  Hank - the force developed is dependent on the

  stiffness of both the bolt material and of the specimen

  you're pushing on.  You can't necessarily
 equate

  this directly to torque because of friction in the bolt

  threads and at the bolt end contact, and of course the

  elasticity of the bolt itself. You can only estimate
 it. 

  There are many online tools for calculating the
 developed

  tensile force in a bolted connection, for example, but
 these

  consider only the bolt as the deformable element, and

  require an accurate estimate of coefficients of
 friction,

  and this will change with lubrication. As you complicate
 the

  system, it becomes more geometry dependent.

  A 1" - 8 UNC 2A thread is 8 threads per

  inch, so a set number of turns will give you the
 approximate

  axial displacement (0.125" per revolution -
 approximate

  because the bolt will change length under load). If you

  assume a rigid fixture, then your strain is equal to
 the

  overall change in length (calculated from # of bolt
 turns),

  divided by the gauge length (distance over which the
 length

  change occurs, which would be the length of your
 specimen

  measured between the rigid fixture and the end of your
 jack

  bolt). Compressive or tensile load is then calculated
 based

  on the modulus of elasticity of the specimen. 

  Alternatively, you can measure the load (make the bolt
 or

  fixture into a load cell or strain gauge the specimen)
 and

  calculate the material properties.

  Load, axial displacement, modulus. You need any

  two to calculate the third.

  What are you making / testing?

  Sean

  On July 6, 2015 6:26:49 AM

  MDT, hank pronk via Personal_Submersibles

  <personal_submersibles at psubs.org>
 wrote:

  Hi all,

  I

  need help, can anyone tell me how to calculate how much

  force a bolt can push or pull using a torque wrench to
 turn

  the bolt. So how many foot pounds of torque does it take
 to

  rotate a bolt to  create 250 lbs push with a 1 in
 coarse

  thread bolt.  I need to make a test fixture.

  Hank

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