[PSUBS-MAILIST] calculation

Mon Jul 6 21:58:30 EDT 2015

Alec, do you know the hardness of the plastic ring.  The Acrylics hand book recommends min duro 80.
Hank--------------------------------------------
On Mon, 7/6/15, Alec Smyth 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, 9:52 PM

 A flat
 ring cut from thin plastic and lubricated with vacuum grease
 on both sides. I'm glad to say it doesn't make any
 sound at all.
 Alec
 On Mon, Jul 6, 2015 at 9:32
 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:

 Alec,

 What is under your dome.

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

 On Mon, 7/6/15, Alec Smyth 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, 8:31 PM

  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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