Propeller;- to key or not to key.

[Graham_Wright]

Currently my prop shaft has no keyway although the intended prop has.

Should I rely on the taper (Mr Morse did with universal success) or should I cut a keyway.

 

[NorthUp]

The keyway and key are essential.

Mr Morse's tool can be removed with a sharp tap..

 

[ffiill]

Taper can be broken with a sudden shock-if securing nut can for any reason move within the contraints of the split pin and often split pin nuts are too small to have multiple casteling and you have to back it slightly to secure spit pin then mechanical taper lock can break and prop spin.
A slightly wobbly prop held by taper is better than free spinning prop!

 

[vyv_cox]

Modern machinery practice is that keys and keyways are not used as they can lead to fatigue fracture. I know of 90 MW turbine driven compressors that have tapered drive couplings without keyways. However, the joints are set up carefully by skilled fitters. You could certainly attach a prop to a shaft without a key but the torque would need to be measured accurately and a fitted spacer washer would be needed to ensure the nut mated up with the drilled hole in the shaft.

 

[GrahamHR]

Why are castellated nuts and split pins still used, rather than an accurately torqued up Nyloc type nut, where it's certain the nut is in contact with the prop ? I've not had any of the Nyloc prop nuts on my DPS drives come loose in 12 years of owning such drives.

 

[Graham_Wright]

Modern machinery practice is that keys and keyways are not used as they can lead to fatigue fracture. I know of 90 MW turbine driven compressors that have tapered drive couplings without keyways. However, the joints are set up carefully by skilled fitters. You could certainly attach a prop to a shaft without a key but the torque would need to be measured accurately and a fitted spacer washer would be needed to ensure the nut mated up with the drilled hole in the shaft.

I was hoping you would reply and I was further hoping you would lean towards no key.

You have done!

 

[earlybird]

Morse tapers are considerably smaller angles than prop-shaft tapers, and almost invariably rely on uni-directional axial load to maintain drive, eg drills.
They're likely to be rather more accurately made than many prop-shaft tapers.
Although it might work, I wouldn't be very happy with no key-way in my stern gear.

 

[Graham_Wright]

Morse tapers are considerably smaller angles than prop-shaft tapers, and almost invariably rely on uni-directional axial load to maintain drive, eg drills.
They're likely to be rather more accurately made than many prop-shaft tapers.
Although it might work, I wouldn't be very happy with no key-way in my stern gear.

I know what my shaft taper is as I turned it myself (CNC). I cannot vouch for the prop taper.

 

[Marsupial]

As others have said if everything is accurately made and properly fitted you MAY be able to do away with the key. The risk you run is the nut undoing when the shaft changes direction quickly and the prop falls off. This can happen (and has happened many times) with a pinned on nut and a shaft keyed so I would be very wary of relying on a taper and a cotter pin as the only security - unless it was bench fitted (lapped and locked).

 

[Jcorstorphine]

What about using some very fine grinding paste and lapping the prop to the shaft and as others have said use, a suitable marne version of a nyloc nut or if there is room, two nuts with the second one as a locking nut.

Mind you, if the prop and the shaft are a very very good match, you may have a problem getting them appart

 

[Graham_Wright]

I think I need to await the return of the jury after their overnight recess!

 

[Norman_E]

Standard prop shaft taper is self releasing, whereas the very shallow angle of a Morse taper allows it to grip such that a sharp blow is needed to release it. The only boat I have seen where the prop fell off had no key, and the prop was lost when the charterer banged it quickly from ahead to astern a few times. My shaft has a keyway, and when I had a fixed prop it not only had a key, but also a tabbed washer with the tab knocked into the keyway in the prop. If I was the OP, I would have a keyway milled into the shaft. The key must be a good close sideways fit in both propeller and shaft, but needs a small vertical clearance.

 

[lw395]

I've known people lose props that are not only keyed, but splined.
Once the nut comes (even slightly) loose. it's all just a matter of time.
I think a prop taper will work, if it matches properly.
You can get some idea by shading the taper with marker pen and putting the prop on. If all the ink is rubbed off, you have good contact.
The key is really there to hold it while you start to do up the nut, according to my Dad, anyway.
Just use the right grade of Loctite.
Not so easy if you're doing it underwater of course.

 

[Rock Dodger]

Morse taper is something like 7 point something degrees and the taper finish should be a ground one with matching finish on mating face. it was designed to be a "binding cone" fit. If the finishes on the internal and external faces of the prop/shaft are good then it might not be an unqualified success. Keys are a tried and tested way of securing a component to a shaft to transmit torque. The spline AND key failing must have been down to axial movement fretting the surfaces which is exacerbated in the corrosive saltwater environment. However, Professor Sod says that if you don't have a belt and braces approach in the marine environment then...

 

[GrahamHR]

What, no expert opinions why a Nyloc type nut can or cannot be used on a taper shaft to prop assembly ? It seems an idiot proof solution to me.

 

[cryan]

Ships did away with keyways just after WW2. Their props are driven up the taper hydraulically. Surely a similar but much smaller system could be used on leisure boats.
The keyway does not stop the prop falling off though. I'm not sure if the Nylock idea would work at the sizes were talking about but stainless locking wire will.

 

[aitchem]

When I was designing Locomotives (70's).
They were replacing the old thick nut + thin nut idea because it was unreliable (installer dependant)
This arrangement was replaced with the Philidas nut.
The aircraft industry use a full thread (tight) nut, looks like a con-rod nut.

 

[Graham_Wright]

Ships did away with keyways just after WW2. Their props are driven up the taper hydraulically.

It is the "Pilgrim Hydraulic Nut". No idea of the cost.

It seems to me that if the nut cannot come undone, at worst the propeller can spin but it cannot fall off. What is wrong with a pin through the shaft on a castellated nut? Accepted that the pin never lines up with the best castellation, the answer surely is to introduce a resilient spacer, a substantial spring washer, between nut and prop boss.

 

[ean_p]

The Morse is one of only many tapers in use in engineering etc...ref the ISO tapers used in machine tool holders and you'll find that the tapers are often much steeper. A problem with a key is that it requires considerably more material in the components then would just a taper so as to accommodate the keyway. This additional material is both expensive and bulky!
Nyloc nuts are generally good but personally I would never use them on a 'vibrating' stainless component as the stainless seems to encourage them to back off because of its 'polished slippy' surface! In addition they are , like 'aero' nuts, really a one use item and more expensive then a tab'd wired or pin'd nut I think which should be pretty foolproof!

 

[earlybird]

The Morse is one of only many tapers in use in engineering etc...ref the ISO tapers used in machine tool holders and you'll find that the tapers are often much steeper. .

Morse tapers are used to transmit torque. The steeper tapers, such as International are for location and are self-releasing, dogs or keys are usual to transmit the torque.