[PSUBS-MAILIST] calculation

[Alan James via Personal_Submersibles]

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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