[PSUBS-MAILIST] Cylinder tolerance

[James Frankland via Personal_Submersibles]

Picture didn’t seem to come through


On Monday, 22 August 2022, James Frankland <jamesf at guernseysubmarine.com>
wrote:

> 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
>>> _______________________________________________
>>> Personal_Submersibles mailing list
>>> Personal_Submersibles at psubs.org
>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>
>>
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