I didn't know there were so many variations of shaft tapers. http://littlemachineshop.com/Reference/Tapers.php
Fortunately it did not leave the shop like that. It has had three different props on it and has been removed from the vessel four times since installation. Each removal requires cleaning the outside of it of growtha nd ocean gunk with a ScotchBrite pad so I can slide the PSS rotor off it.... It looked a lot better when I first installed it with the original prop.no shaft would leave my shop like the one in the first picture. we call that a pittsburg finish. probably said oops!
They don't! And Mainesail is as fussy about that fit as he is about the prop to shaft fit.How do the rotational sheer forces on the shaft-prop interface differ from the forces of the shaft coupling?
Your statement highlights the differences between essentially the old British "Whitworth System" and the "American Standard - ANSI". The "American Standard" largely depends on the perfect (forced together) mating surfaces of a ~10 degree taper to transfer ALL the torque load by friction between the mating surfaces; the Whitworth also depending (necessarily) on 'keys', etc. Machining tolerances, although improved by modern tooling and methods, still are 'tolerances' which imply surface 'mismatch' with the probability of 'point-to-point-contact; whereas, lapping lessens the point-to-point contact and better insures total surfaces contact .... and more predictable or reliable 'friction/intereference fit'.Maine,
The original machining tolerances should enable a satisfactory fit without need for grinding in and certainly trueness and balance should be unaffected.
Unless you have an amateur prop or shaft job the tapers should already be to the relevant standards which guarantee a correct fit.
Also I would be wary of grinding the surface of my prop shaft as it would then not be a correct fit for any subsequent prop and I would not want a depressed area where the old prop sat on the shaft.
I even delude myself with the hope that having a microscopic gap between the prop and shaft will allow enough water circulation to prevent the shaft suffering concentrated cell corrosion, otherwise known as crevice corrosion and being corroded away through lack of oxygen.
ONLY applicable on non-tapered shafts. On properly designed/engineered tapered shafts the key is only a 'back-up or safety'.I believe they call that torque or just plain old shear. It should be taken primarily by the key. The lap fit is just to keep everything solid.
The shear force on the key is the toque supplied x radus of the shaft / area of the key. The area being what would be left of the key if you sheared it off. Which is why you should not skimp on the key.
The torque on the coupling is torque supplied X radus of the connecting bolt holes from the center of the coupler / sum of the bolt areas along the shear line. A much larger area and radus to shear through so this part will probably hang in there as the prop key goes south. Course if you have a very high strength steel in the key and low strength in the coupling bolts you could get the coupling to go first.
So if it required to have a tapered lapped fit on the prop end of the shaft, than why not on the coupling end as well?They don't! And Mainesail is as fussy about that fit as he is about the prop to shaft fit.
No place for the nuts! Not all propellers are fitted to a tapered shaft some outboard motor props slid easily onto a straight shaft and were driven by a shear pin that could be easily replaced. High power outboards and stern drives are usually spline driven. With a straight shaft you must have a shoulder to support the prop against the clamping force of the nut. On outboards with shear pins the nut tightened against a shoulder on the shaft and served only to keep the prop on the shaft but the drive was strictly by the shear pin.So if it required to have a tapered lapped fit on the prop end of the shaft, than why not on the coupling end as well?
Most larger and high horsepower shafts do have a taper and nut at the coupling end.So if it required to have a tapered lapped fit on the prop end of the shaft, than why not on the coupling end as well?
Because builders and customers don't want to pay for it. Sabre Yachts / Back Cove specifies double tapers on all their shafts and they are all made at my friends shop here in Maine and all are double taper, sail & power. I have seen double tapers on lots of higher end sailboats.So if it required to have a tapered lapped fit on the prop end of the shaft, than why not on the coupling end as well?
Ross this is not the case, the nuts are well hidden inside the coupling and there are a number of ways they can be attached without the typical "prop" type nuts.No place for the nuts!