[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PSUBS-MAILIST] thru hull fittings
Brian,
No, no Not at all.
Either O-rings on the shaft, or O-rings in the housing will work. As far as
leaking, it's the shaft to housing clearance and the proper groove depth
that matter. And yes, hydraulic applications do sometimes use O-rings in a
shaft but not as a rule. If the shaft is the critical component, the O-ring
grooves are in the housing. Grooves in a shaft weaken it.
Maybe I didn't explain myself well before. What I meant by my earlier
posting was, if you groove the shaft, the groove diameter, minis a little
factored in for the stress risers created by the groove, becomes the working
diameter of the shaft. The weakest point! A groove does create stress
riser. If you break a shaft with grooves in it, it will always fail in one
corner of a groove. A properly designed O-ring groove has small radii in
it's corners, but still it's a week spot. If you take the same shaft size,
but put the O-ring in the housing, you can design around the full shaft
diameter.
I tried to keep my shaft diameters from getting larger then needed because,
as a shaft get larger it takes more force to turn when your deep. At 400
feet a one inch shaft has 160 pounds of force pushing in on it. That
creates friction that you have to overcome to turn it.
Dan H.
----- Original Message -----
From: "Brian Cox" <ojaibees@ojai.net>
To: <personal_submersibles@psubs.org>
Sent: Sunday, February 29, 2004 12:14 PM
Subject: Re: [PSUBS-MAILIST] thru hull fittings
> Hi Dan,
> I knew that would draw a response ! I really don't
follow the reasoning on this. I simply do not understand what you are
saying. Don't most hydraulics have the O rings on the the shaft and with
those we're talking 3000 psi. If I had the O rings on the shaft are you
saying that I would not be able to turn the shaft? And the O ring would
leak because there is more stress on the corners of the O ring grooves? I
don't get it ! Sorry to be so difficult and annoying !
>
> Brian
> ----- Original Message -----
> From: "Dan H." <jmachine@adelphia.net>
> To: <personal_submersibles@psubs.org>
> Sent: Sunday, February 29, 2004 5:19 AM
> Subject: Re: [PSUBS-MAILIST] thru hull fittings
>
>
> > Brian,
> > O-rings on the shaft create areas of higher stress in the corners of the
> > O-ring grooves. Also your shaft diameter is the area that the sea is
acting
> > on when calculating how much force is pushing inward on the shaft. At
depth
> > that force creates some resistance to turning. But, for sheer, tension
and
> > compression, your shaft diameter is only the root to the O-ring groove
minus
> > a bit for the stress risers in the groove corners.
> >
> > It's a bit more difficult putting the O-rings in the thru hull, but the
> > shaft in one size and most efficient.
> >
> > Dan H.
> > ----- Original Message -----
> > From: "Brian Cox" <ojaibees@ojai.net>
> > To: <personal_submersibles@psubs.org>
> > Sent: Saturday, February 28, 2004 6:54 PM
> > Subject: Re: [PSUBS-MAILIST] thru hull fittings
> >
> >
> > > Dan, thanks for the insite, I'll probably go bigger on the drop
weight.
> > My "O" rings are going to be on the shaft.
> > >
> > > Brian
> > > ----- Original Message -----
> > > From: "Dan H." <jmachine@adelphia.net>
> > > To: <personal_submersibles@psubs.org>
> > > Sent: Saturday, February 28, 2004 5:50 AM
> > > Subject: Re: [PSUBS-MAILIST] thru hull fittings
> > >
> > >
> > > > Brian,
> > > >
> > > > You sound like your on the right track with your through hulls. One
> > thing
> > > > to consider with your drop weight through hulls is, how your going
to
> > attach
> > > > the handle inside the sub. If your going to drill through the shaft
you
> > may
> > > > want to consider a shaft larger then a half inch since it's holding
the
> > drop
> > > > weight and will get yanked through the hull if it breaks or of the
bolt
> > > > shears. When making mine, I was visualizing the drop banging up and
> > down on
> > > > it's shaft while tailoring down the road. Then I want to depend it
to
> > hold
> > > > the weight when diving.
> > > >
> > > > I had a bit of trouble with the through hulls necking down in the
weld
> > area
> > > > but cured the problem with a hand reamer after welding. Use two
> > O-rings,
> > > > one near each end, for double protection and then you won't be
welding
> > or
> > > > reaming where they will be.
> > > >
> > > > Dan H.
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "Brian Cox" <ojaibees@ojai.net>
> > > > To: <personal_submersibles@psubs.org>
> > > > Sent: Saturday, February 28, 2004 1:00 AM
> > > > Subject: Re: [PSUBS-MAILIST] thru hull fittings
> > > >
> > > >
> > > > > Alec, If I'm envisioning that piece correctly it started out as
a
> > 1.5"
> > > > dia shaft and a portion was machined down to 1" , then the part is
> > inserted
> > > > from the outside of the sub where the lip keeps the part from
blowing
> > into
> > > > the sub under pressure. I probably don't have your dimensions quite
> > right
> > > > but I think I see the part. Are the shaft and hole 1" +/- 2
> > thousandths?
> > > > >
> > > > > Brian
> > > > > ----- Original Message -----
> > > > > From: "Alec Smyth" <Asmyth@changepoint.com>
> > > > > To: <personal_submersibles@psubs.org>
> > > > > Sent: Friday, February 27, 2004 4:28 PM
> > > > > Subject: RE: [PSUBS-MAILIST] thru hull fittings
> > > > >
> > > > >
> > > > > > Yes, there's a reason. Because the sub is hydrobatic, when the
sub
> > is at
> > > > a 90 degree roll the drop weight will exert a bending moment. So I
made
> > it
> > > > stubby. The maximum diameter is 1.5", and its set in an insert that
is
> > 3" in
> > > > diameter. The difference between the diameters of the shaft and the
hole
> > is
> > > > only 2 thousandths of an inch, so that the O rings cannot extrude
and so
> > the
> > > > insert will help the shaft resist the bending moment. And the reason
I
> > said
> > > > "maximum diameter" is that there is a 1" section on the shaft too,
to
> > > > prevent the ambient pressure from shooting it into the boat after
> > releasing
> > > > the drop weight, or when the sub is inverted.
> > > > > >
> > > > > > Sorry for writing a book on such a small topic...
> > > > > >
> > > > > > Alec
> > > > > >
> > > > > > -----Original Message-----
> > > > > > From: Brian Cox [mailto:ojaibees@ojai.net]
> > > > > > Sent: Fri 2/27/2004 5:40 PM
> > > > > > To: personal_submersibles@psubs.org
> > > > > > Cc:
> > > > > > Subject: Re: [PSUBS-MAILIST] thru hull fittings
> > > > > >
> > > > > >
> > > > > >
> > > > > > Thanks Alec, I read a few posts back that your drop weight
shaft
> > was
> > > > like 2" or something, it seamed rather large was there some reason
for
> > > > that?
> > > > > >
> > > > > > Brian
> > > > > > ----- Original Message -----
> > > > > > From: "Alec Smyth" <Asmyth@changepoint.com>
> > > > > > To: <personal_submersibles@psubs.org>
> > > > > > Sent: Friday, February 27, 2004 1:28 PM
> > > > > > Subject: RE: [PSUBS-MAILIST] thru hull fittings
> > > > > >
> > > > > >
> > > > > > > With a 1.25" insert, you have added much more reinforcement
than
> > the
> > > > material you removed with a 0.5" shaft hole. If I remember right,
the
> > rule
> > > > of thumb is that you should add twice as much as the hole removed.
So it
> > > > should be sufficient.
> > > > > > >
> > > > > > > Alec
> > > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Brian Cox [mailto:ojaibees@ojai.net]
> > > > > > > Sent: Fri 2/27/2004 3:51 PM
> > > > > > > To: Personal_Submersibles@psubs.org
> > > > > > > Cc:
> > > > > > > Subject: [PSUBS-MAILIST] thru hull fittings
> > > > > > >
> > > > > > >
> > > > > > > Hi All, I am in the process of machining thru hull fittings
> > (316L
> > > > ss) that will have 1/2" shafts running through them to turn valves,
turn
> > > > rudders, and other functions as well, drop weight, and possibly move
> > trim
> > > > ballast ;-) . The fittings that I am machining at the moment
are 1
> > 1/4"
> > > > od with the 1/2" id ( for the shaft) is that 1 1/4" a big enough
> > chunk of
> > > > steel to be welded through 1/4" A516 70 or should that OD be
larger
> > for
> > > > some reason?
> > > > > > >
> > > > > > > Thank You
> > > > > > >
> > > > > > > Brian Cox
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > >
> >
> >
> >
>
>