[PSUBS-MAILIST] Jon's new penetrators

[Sean T. Stevenson via Personal_Submersibles]

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 look 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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