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Re: [PSUBS-MAILIST] thru hull fittings
Hi Brian,
I was interpreting this as O-rings on the shaft make the shaft weaker (the shaft is
only as strong as it's narrowest point). On top of the narrow point weak spot, you've
also got 'notch test' type weakness since the O-ring groove will act like a notch in
the steel, further reducing the strenght of the shaft.
Ian.
-----Original Message-----
From: Brian Cox <ojaibees@ojai.net>
Sent: Feb 29, 2004 9:14 AM
To: personal_submersibles@psubs.org
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
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> > >
> >
>
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