How Y-Size of Coupling is Calculated?

[jaysomlam]

We are trying to use CAMduct to fabricate Couping.  But we have a hard time setting up Coupling to get the correct Y-Size.

Here, we use 10" diameter of Coupling with male connectors (Sex Type is Female) as an example.  Our shop expects the Y-Size of this Coupling to be 32.023".  But CAMduct shows that its Y-Size is 32.10994".  We want to adjust its to get its Y-Size to be as close to 32.023" as possible.  But that is where I cannot find a way to do.

The following is the details of this Coupling with male connectors:
1.  10" diameter.
2.  Male connector has -0.125" Diameter Adjustment.
3.  The seam has 0.5" Male Allowance and 0.5" Female Allowance.

I do this to calculate the circumstance:
  ( Diameter + Diameter_Adjustment ) * Pi
And that is:
   ( 10" - 0.125" ) * 3.1416 = 31.023"
And the Y-Size should be:
   Circumference + Male Seam Allowance + Female Seam Allowance
And that is:
   31.023" + 0.5" + 0.5" = 32.023"
And that is how our shop expects the Y-Size to be.

But CAMduct comes up with 32.10994".  It is 0.0867" more than what we have expected.  Please see the attached picture to see the Y-Size that CAMduct comes up with.  Please also note that this 0.0867" difference remains unchanged when I increase the diameter.  Seem like somewhere in CAMduct or in our Fabrication Database adds 0.0867" to Y-Size for coupling.

Please let me know how CAMduct calculates the Y-Size.  Then I can adjust the settings accordingly to get the correct Y-Size.  Thanks.

Jaysam

[PipeFitter72]

When you make one does it fit correctly?

[jaysomlam]

The shop manager told me that this small difference will make a difference in term of fabrication and fitting.

Jaysom

[PipeFitter72]

My only suggestion is to change the diameter adjust for the connector to make it what you want. No idea other than that.

[jaysomlam]

Unfortunately changing the Diameter Adjust of the connector cannot remove the extra 0.0867" found in Y-Size of Coupling-Male.  We can see the result from the attached picture.  The Diameter Adjust only affects the calculation of the circumference.  Seem like that 0.0867" is added to the Y-Size _after_ the calculation of the circumference.  And I still don't know where that 0.0867" comes from.

0.0867" is less than 1/10".  I will have to convince the shop manager that the small 0.0867" is too small to make a difference.

Jaysom

[jaysomlam]

Seem like I can work around this problem by assigning a small seam allowance.  This surely will work.

This won't actually fix the problem.  But a workaround is good enough for me.

Jaysom

[jaysomlam]

Previously I said changing the Diameter Adjust of the connector cannot remove the extra material found in Y-Size of Coupling-Male.  I was wrong.  I calculated the expected Y-Size incorrectly.  This caused the expected Y-Size to be a "moving target".  Actually, the expected Y-Size for a given diameter should be fixed, not a moving target.

Once I realize my mistake, I can change the Diameter Adjust to compensate for the extra material found in Y-Size of Coupling-Male.

I could have done the same thing by reducing the seam allowance.  But the shop prefers to change the Diameter Adjust instead of seam allowance.  The reason has to do with the fact that this is easier to understand how we can use the Diameter Adjust to shrink the diameter of the coupling.

As for whether the small extra material is something that we can live with or not.  The answer is NO.  The small amount of extra material can make the connection too tight to fit.

I believe this should conclude this issue.

Jaysom

[DamCam]

Dia. adjust -.161 works great for us.