What material should shaft keys be made from?

[crabcake]

Originally Posted by atoll

I've lost count of the times I have had to dive over the side mid ocean and cut away rope,netting or plastic after the engine has been stopped dead,never had a problem with a transmission due to stoppage.

I would hate to have to try replace a key way on a bobbing boat every time something got in the prop

These work!

[Freemind]

The one and ONLY purpose of a key is to protect the rest of what ever machinery it is installed on.
It is meant to shear to prevent damage to more expensive parts.

Use harder material at your own risk. Machinists and mechanics need to make a living too.

Freemind <-- machinist 25 years

[seasick]

Monel shaft Monel key

[Cheechako]

I've had Bronze and had stainless. Not sure it matters much. Your prop is bronze, your shaft is likely stainless, so the key either matches one or the other. Unless you are one of those lucky people with a monel shaft.... A bronze one may come out easier when you are changing.
I doubt a bronze key is much more forgiving than a SS one. It's not like a cotter pin in a small outboard prop.

[model 10]

Originally Posted by Freemind

The one and ONLY purpose of a key is to protect the rest of what ever machinery it is installed on.
It is meant to shear to prevent damage to more expensive parts.
Freemind <-- machinist 25 years

Where did you hear that? I'm picturing a gear or a flange or a pump impeller all driven by a key. There would be no way for the part to turn if it were not for a key. I'm not talking about a tapered shaft. If you are worried about something freezing up they usually put a shear spot on the accessory shaft or a shear pin perhaps. I'm not sure you can shear a key anyway without ruining something

[Sailorbob8599]

My prop shop supplied a 1" dia shaft and a 13" Campbell-Sailer prop and a BRONZE key for my 12 hp BMW diesel engine. These people have been in the business for eons serving both commercial and pleasure craft owners. I would never question their judgement.
FYIW dept: - The key is a tight fit in the shaft but a slide fit for the prop as commented by an earlier posting.

[Freemind]

Originally Posted by Guy

Where did you hear that? I'm picturing a gear or a flange or a pump impeller all driven by a key. There would be no way for the part to turn if it were not for a key. I'm not talking about a tapered shaft. If you are worried about something freezing up they usually put a shear spot on the accessory shaft or a shear pin perhaps. I'm not sure you can shear a key anyway without ruining something

I didn't have to hear it. I've done thousands of repair jobs in a machine shop in my life. Yes you probably will damage the keyway in your prop when it shears. The alternative is putting undue stress on a shaft or gears etc.
I've read here of engines coming to a dead stop from something getting in the prop. Do you really think that there isn't any harm in that? A shaft or gear doesn't have to "let go" to be damaged. The accumulated wear and stresses from being jerked to a stop several times is going to cause a big problem eventually.
Personally (and as a machinist I can't believe I'm saying this ) I'd trust the engineers who designed the system and use what the factory recommends.
Peace

[a64pilot]

I don't want to insult anyone, but when fitting a prop, first install it without the key and make a mark, then when you use the key ensure the prop goes all the way back to the mark you made on the shaft, I've seen keys be a little big and prevent the prop from fully seating.
Sorry for stating the obvious, just thought some one may not know


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[Sailorbob8599]

Quote:
"Originally Posted by Guy View Post
Where did you hear that? I'm picturing a gear or a flange or a pump impeller all driven by a key. There would be no way for the part to turn if it were not for a key. I'm not talking about a tapered shaft. If you are worried about something freezing up they usually put a shear spot on the accessory shaft or a shear pin perhaps. I'm not sure you can shear a key anyway without ruining something"

Response:
I didn't have to hear it. I've done thousands of repair jobs in a machine shop in my life. Yes you probably will damage the keyway in your prop when it shears. The alternative is putting undue stress on a shaft or gears etc.
I've read here of engines coming to a dead stop from something getting in the prop. Do you really think that there isn't any harm in that? A shaft or gear doesn't have to "let go" to be damaged. The accumulated wear and stresses from being jerked to a stop several times is going to cause a big problem eventually.
Personally (and as a machinist I can't believe I'm saying this ) I'd trust the engineers who designed the system and use what the factory recommends.
Peace
_____
With regard to this 2 way discussion, I can see a key being the shear point on a straight shaft assembly, but surely a taper shaft application is different in that the prop would fit very tight on the taper, and highly unlikely to move even in the event of coming to a sudden stop??? Or am I mistaken on this??? Just asking ...

[Cadence]

Originally Posted by Sailorbob8599

My prop shop supplied a 1" dia shaft and a 13" Campbell-Sailer prop and a BRONZE key for my 12 hp BMW diesel engine. These people have been in the business for eons serving both commercial and pleasure craft owners. I would never question their judgement.
FYIW dept: - The key is a tight fit in the shaft but a slide fit for the prop as commented by an earlier posting.

You have the right idea, Listen to someone that has been in the business for eons. You don' stay in business handing out bad advice.

[Ziggy]

Originally Posted by Cheechako

[...]I doubt a bronze key is much more forgiving than a SS one. It's not like a cotter pin in a small outboard prop.

Actually, I agree with that. The yield strength of bronze is not that different from stainless. I would still go with a bronze key on a stainless shaft to avoid any possibility of galling. The prop nut should also be bronze, by the way, for the same reason.

[Cadence]

Originally Posted by Ziggy

Actually, I agree with that. The yield strength of bronze is not that different from stainless. I would still go with a bronze key on a stainless shaft to avoid any possibility of galling. The prop nut should also be bronze, by the way, for the same reason.

For what it is worth. Wait someone will add something about a Rockwell on both.

[Captain Bill 3]

In 30 years of fitting new and used props I have never used any key other than BRASS, not bronze or SS. For conformation contact Miller Island Propeller in Baltimore, MD.

[steve77]

Originally Posted by Captain Bill 3

In 30 years of fitting new and used props I have never used any key other than BRASS, not bronze or SS. For conformation contact Miller Island Propeller in Baltimore, MD.

Capt Bill - You are the first person to recommend brass as the key material. Is there an advantage to brass over other materials? Most of the other folks say stainless or bronze.

I'm not an authority, but I thought brass in contact with a stainless steel shaft and a bronze prop in salt water would be a bad combination.

Thanks!

Steve

[Ziggy]

Steve,
The terms "brass" and "bronze" are used for many copper alloys and are not very precise. For example, "red brass" (85% copper, 5% each of lead, tin, and zinc) is a type of bronze and is quite corrosion resistant.
Z.