[PSUBS-MAILIST] Jon's new penetrators

[Sean T. Stevenson via Personal_Submersibles]

When fits really matter, as in high precision running machinery or critical transitional fits, a prudent designer will actually specify the part temperature at which the drawing annotations apply. For example, 20°C (normal / typical room temperature), or my preference, 0°C (standard temperature / icewater bath), which allows a machinist to quickly bring all parts to a common reference temperature for measurement.  Even if that note is not used for manufacture, it provides a basis for rejection of the part during QC measurements when it is supplied close to a tolerance limit.

Sean


On February 15, 2016 12:14:45 PM MST, "Sean T. Stevenson via Personal_Submersibles" <personal_submersibles at psubs.org> wrote:
>I typically specify fits using the ISO notation including tolerance
>limits. For a penetrator, you aren't really concerned about location,
>but your diameters will matter because of the O-ring sealing
>tolerances. In that case, as a part fit I might specify something like
>an H9/d9 fit, which you can look up the tolerances for on the basis of
>the nominal size - certainly this would be sufficient for the tolerance
>on the shaft diameter, but you might be forced to control more tightly
>on the hole diameter in order to hold the minimum acceptable O-ring
>compression in conjunction with the depth of the groove(s) on the
>shaft. The selected fit class will also dictate the minimum / maximum
>extrusion gap, which you may have to control. Are you using the Parker
>O-ring guide as a reference? That should specify the required
>tolerances. Just select a corresponding hole/shaft fit class that makes
>it work out. As for temperature variation, I think you will find it is
>negligible, but you can l!
> ook up
>the coefficient of thermal expansion for both materials and use your
>maximum anticipated temperature range to calculate the delta - keep in
>mind that both sides will experience approximately similar temperatures
>in service, so you need only concern yourself with the dimensional
>change of the completed assembly between temperature extremes. If it
>turns out to matter, you rein in your tolerance limits accordingly, but
>I suspect it will be a non-issue.
>
>Sean
>
>
>On February 15, 2016 11:42:33 AM MST, Jon Wallace via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>I found a reference to it online.  Since these are non-rotating parts
>>it 
>>looks like Class 3 or 4 would work, but I suspect the snugness at any 
>>given moment of time will depend upon temperature with very close 
>>tolerances.
>>
>>Jon
>>
>>
>>On 2/15/2016 10:25 AM, Sean T. Stevenson via Personal_Submersibles
>>wrote:
>>>
>>> Jon, do you have a copy of the Machinery's Handbook? Standard fits
>>and 
>>> tolerances for hole based and shaft based fits in nominal sizes in 
>>> both inch and metric are covered. I can look it up for you on
>Tuesday
>>
>>> if you like. Regardless, get a copy of that book if you don't have
>>one.
>>>
>>> Sean
>>>
>>>
>>
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>
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