[PSUBS-MAILIST] Cylinder tolerance

[Alec Smyth via Personal_Submersibles]

Hi James,

The ABS rules specify two conditions. First, that the out of roundness does
not exceed 1% of the diameter. The second is more complicated. There's a
table with a coefficient on each axis, showing curves of allowable
eccentricities. That table takes into account more variables than the first
rule (for instance, the length of the cylinder.) I'll attach two images in
low res, in the hope they are under the mailing list attachment limit that
way. Probably the simplest way to spec a cylinder is just to use the 1%
rule.

In practice, I found this a very tricky fabrication issue. The cylinder was
supplied rolled but not welded, and although I don't recall its
eccentricity I'm sure it was nowhere near 1% initially. I stretched the
cylinder into roundness with the stiffeners, rolling them in along the
greater diameter and then rotating them. Their fit was so tight, and the
forces needed to stretch the cylinder so great, that it took several months
of work to get them in.

Hopefully this comes through with two attachments, but if it doesn't let me
know and I'll email them directly.

Best,
Alec



On Sun, Aug 21, 2022 at 11:58 AM James Frankland via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hi All
>
> Im getting some quotes in for some rolled cylinders.
>
> What do people think i should ask for as the tolerance on roundness?
>
> I believe (from memory) that the K350 plans specified "cylinder to be
> within 1/8th (3.175mm) on diameter for a 3ft (914mm) shell .
>
> im quoting for a 650mm inside diameter 10mm cylinder.
>
> Im feeling i want to ask for 1mm on diameter.
>
> What do you guys think?
>
> Thanks
> James
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> Personal_Submersibles at psubs.org
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>
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