[PSUBS-MAILIST] Cylinder tolerance

[James Frankland via Personal_Submersibles]

Hi
The idea is to make a small simple sub that I can operate and launch
alone.  I think I could make something like this pretty quick.
I’m just getting prices to see if it’s feasible.  Kind of based the idea on
c-bug, R300 and deep flight dragon.
Cylinder is 650mm x 2000 unstiffened.   Hence the thickness.  Tower 6mm.
The fins are not intended to be diving planes or control surfaces.  The 4
motors would rotate and the sub simply drive about on the motors.  The fins
are really just for looks....

Just an idea at this stage.

Alec.  Yes the pics came through thanks.  Could you send me the whole page
with the diagram it refers to.?  Thanks.

Vance.  I will have it written into the contract the tolerance, so if it’s
out, I can refuse it.

1% of 650 is 6.5mm allowed.  Seems a lot to me....

Just ideas at this stage.  Criticism and thoughts welcome.
Regards
James


On Sunday, 21 August 2022, Alec Smyth via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> 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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>>
>
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