The only thing that immediately comes to mind is that the shaft diameter is presumably sized to accomodate the design loads in torsion, bending and shear, and that cutting o-ring grooves into it without decreasing its strength necessitates upsizing the shaft diameter, which for a shaft of unspecified length is probably more expensive than machining these grooves into a bore which is only long enough to serve as a through-hull. Any grooves cut in a shaft will serve as stress concentrations, which may be of concern or not depending on the shaft loading, but a through-hull bore typically does not carry any torsional loads, rendering any such machining in the bore as less of a concern. Additionally, (and I say this having never seen the K350 drawings, so pardon me if these comments are not applicable), the contact sealing surface must be tightly controlled in both surface finish and roundness, which is a lot easier to do on a shaft which can be machined on a lathe (or in fact, repaired after being damaged through weld deposition and re-machining), versus a through-hull bore which is either machined in situ, or machined in the shop and subsequently welded, leading to possible distorsion.
-Sean
On Apr 6, 2010, Scott Waters <muddywatersfarm@hotmail.com> wrote:
For the rotating tru hulls the K-350 design shows to put a internal groove inside the collar and the o-rings are inserted and seated in it. I know I heard a few people saying you can do the opposite and put the grooves on the shaft and seat the o-rings there, however it will take a different size of o-ring. Is this ok to do? I don't see any problems with it, but I may be overlooking something. It seems it would be easyier to lathe, and easyier to service the o-rings. Also, before I do this, is there any special kind of o-rings, or will the ones you get at the hardware store work (as long as the mesurment tolarences are correct).
Thanks,
Scott Waters
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