[PSUBS-MAILIST] Clearances

Tue Dec 10 23:56:25 EST 2024

Hank, what you're proposing sounds totally logical to me. However, I have
asked Greg this very question in the past (whether we really have to anneal
a viewport.) I'm not sure what the underlying causality is, but he has
enough professional experience in the field that I just take his word for
it. "You need to re-anneal it whenever any machining has been done on a
viewport." Annealing is pretty straight forward.

I'm currently working on forming acrylic headlight covers and windows for
an antique car restoration. It's a new skill I'm trying to develop, so
fortunately I'm not making anything safety-critical like viewports. But one
interesting detail is that Greg strongly recommended annealing even for
this, because it'll make the covers and windows less likely to crack (there
could be stresses caused by mounting screws or flying pebbles, for
instance.) He had two basic points he stressed for the things to last:

1) That not all acrylic was equal. The only one he will use is "cell cast"
acrylic, and he warned me emphatically to stay away from the cheap stuff
which can be referred to as extruded or "continuous cast." I know this has
not been mentioned on this thread, but I bring it up because it seems to be
key information.
2) Annealing

Next time I speak to him, I'll ask about machining with light passes and
coolant.

Best,
Alec

On Tue, Dec 10, 2024 at 1:35 PM hank pronk via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Rick, I would do some more research on annealing your port again.  If I
> recall, a window is only allowed one annealing cycle.  The reason for
> annealing after machining is due to heat build up for machining.  I have
> machined and tested ports without an annealing cycle.  The trick is to take
> super small passes .005 and even spray water on it as its  cutting.   I was
> talking to a machinist one time about machining domes and he put ice water
> in the dish to keep it cool.
> Its been a while since I worked on this, so check it out, in case my
> memory is off.
> Hank
>
> On Tuesday, December 10, 2024 at 10:55:04 AM MST, Rick Patton via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> Hey Sean,
> The viewports are flat. Thanks for the data.
>
> On Tue, Dec 10, 2024 at 6:12 AM Sean T. Stevenson via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Rick, is this a flat disc viewport, and not a dome?
>
> See an excerpt from ASME PVHO-1-2023 below. *Do*, where referenced, is
> the window major diameter.
>
> * 2-2.11.4 Flat Disk Windows*
>
> *2-2.11.4.1 Window External Diameter.*
>
> The dimensional tolerance of the external diameter of the window shall be
> based on the type of sealing arrangement for the window.
>
> * (a)* The external diameter of the flat disk window shall be within
> +0.000/−0.010 in. (+0.000/−0.25 mm) of the nominal value if the window is
> to be sealed in the seat cavity with a radially compressed O-ring.
>
> * (b)* The external diameter of the flat disk window shall be within
> +0.000/−0.060 in. (+0.000/−1.5 mm) of the nominal value if the window is to
> be sealed in the seat
> cavity with a seal ring wedged into the annular space between the
> retaining ring, the window’s bevel, and the cylindrical surface of the seat
> cavity.
>
> * (c)* The external diameter of the flat disk window shall be within
> +0.0/−0.125 (+0.0/−3.2 mm) of the nominal value if the window is to be
> sealed in the seat cavity with a flat elastomeric gasket axially compressed
> by the retaining ring.
>
> * (d)* The external diameter of the flat disk window shall be within
> +0.00/−0.02 *Do* of the nominal value if the window is to be sealed in
> the seat cavity with a room temperature curing elastomeric compound
> injected into the annular space between the edge of the window and the
> cylindrical surface of the seat.
>
> * (e)* The plane bearing surface of the flat disk window shall not
> deviate more than 0.001 *Do* from an ideal plane.
>
>
> *2-2.11.4.2 Seat Cavity Diameter.*
>
> The dimensional tolerance on the external diameter of the window seat
> cavity shall be based on the type of sealing arrangement for the window.
>
> *(a)* The diameter of the seat cavity for a flat disk window shall be
> within +0.01/−0.00 in. (+0.25/−0.00mm) of the nominal value if the window
> is to be sealed in the seat cavity with a radially compressed O-ring.
>
> *(b)* The diameter of the seat cavity for a flat disk window shall be
> within +0.06/−0.00 in. (+1.5/−0.00mm) of the nominal value if the window is
> to be sealed in the seat cavity with a seal ring wedged into the annular
> space between the retaining ring, the window’s bevel, and the cylindrical
> surface of the seat cavity.
>
> *(c)* The diameter of the seat cavity for a flat disk window shall be
> within +0.125/−0.000 in. (+3.2/−0.00mm) of the nominal value if the window
> is to be sealed in the seat cavity with a flat elastomeric gasket axially
> compressed by the retaining ring.
>
> *(d)* The diameter of the seat cavity for a flat disk window shall be
> within +0.01 *Do */−0.000 of the nominal value if the window is to be
> sealed in the seat cavity with a room-temperature curing elastomeric
> compound injected into the annular space between the edge of the window and
> the cylindrical surface of the seat.
>
> *(e)* The plane bearing surface of the seat cavity shall not deviate more
> than 0.002 *Do* from an ideal plane when measured with a feeler gauge
> inserted between the mating plane surfaces of the flat disk window or a
> circular plug gauge and the bare seat cavity. The axial force used to seat
> the window or the plug gauge shall not exceed 10 *Do* lb (4.53 *Do* kg)
> applied uniformly around its circumference.
>
> Sean
>
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