Reboring and Rekeying a Prop

[mikogold]

how would that work? 1 1/8 is smaller than 30mm

[bobconnie]

Ahh , ya might try and leave the key out sometime, and then you will know WHY they go to all that trouble to put the keyway in the taperd hole !!LOL just kidding ya HAVE to have a keyway, or you will never get the prop to stay in one spot !

[bobconnie]

And the reason they are taperd is to be able to locate them on the shaft without useing a stright shaft with threads and nuts and so on, ya have a taper which picks the spot where the prop will run ! It is then held in place by the key, and the lock nut and cotter key. It's much easier to do a taperd shaft in a lathe, then trying to bild a system of nuts and threads and spacers!

[Andrew Troup]

If the key is doing all the work, the machinist made a poor job of the taper. Or the nut has come loose .... that's my take on it, at least.

It's relatively difficult to use a shallow taper to dictate where the prop ends up. If that was my concern, I'd machine a shoulder on the shaft for the prop to pull up against, and provide a cylindrical bore in the prop, locating on a cylindrical register on the shaft.

To my way of thinking the taper serves two purposes:
1) It transmits the lion's share of the torque, which the key is frankly inadequate to do

2) It takes up all the radial clearance in the joint, the chief benefit being that there can be no fretting (which is what it's called when the prop nutates or orbits relative to the shaft, exploiting the tiny clearance which is almost inevitable in a cylindrical joint).

Fretting rubs off material on the shaft, the prop, or both.

[model 10]

An anal machinist will lap a taper to the point that they get almost 100% contact on a taper. If you blue a machined taper it will not be even close to that. At 100% contact, I bet you don't need a key except to index the propeller.

[mikogold]

what is an "anal machinist"?????????????????????

[Andrew Troup]

It's a tautology

[model 10]

Originally Posted by mikogold

what is an "anal machinist"?????????????????????

I'm sorry. What I should have said was, a very picky machinist would work and work till he got a perfect fit. Probably working at it more than he really needed to.. Not sure that's an example of a tautology but maybe so.

[fstbttms]

Originally Posted by emcmia

A prop shop such as Frank & Jimmies in FLL sells a tapered spacer specifically designed for SAE to metric conversions. No machining needed. I have two spare props originally sized for 1 1/8 that I have fitted to my 30mm shafts. In 2009, they were about $30 each. I'm sure other sizes are available.

The OP wants to go smaller to larger, not the other way around.

[NoTies]

Originally Posted by bobconnie

And the reason they are taperd is to be able to locate them on the shaft without useing a stright shaft with threads and nuts and so on, ya have a taper which picks the spot where the prop will run ! It is then held in place by the key, and the lock nut and cotter key. It's much easier to do a taperd shaft in a lathe, then trying to bild a system of nuts and threads and spacers!

I'm sorry Bob but I believe you are posting misleading information. The shaft taper surface area is what transmits the drive, the key is simply a locating tool. Many engines, including Cat, Cummins etc drive their injector pump via a tapered shaft with no key at all, to facilitate timing. This is the reason why you do not grease the taper on a prop or coupling. They will likely come loose if you do.

[fstbttms]

Originally Posted by NoTies

...the key is simply a locating tool.

In the case of a sailboat prop shaft, what is being located? The prop's orientation on the shaft is irrelevant.

[Andrew Troup]

The key stops the prop turning during the time the nut is taking up (the taper won't transmit torque until the nut pulls it tight)

The key also buys a bit of time if the nut works loose, otherwise a right hand prop, assuming you're going ahead, will immediately run the nut right off the thread, and follow it into the depths.

[Nor'Sea 27]

The keystock is just a safety in a taper joint case. Lapp the taper joint (90% is minimum contact in my book.) Heat and install. This is obviously not an underwater case.

I always wonder how does FastBottoms do a well lapped propeller install?

Charles

[model 10]

Originally Posted by NoTies

I'm sorry Bob but I believe you are posting misleading information. The shaft taper surface area is what transmits the drive, the key is simply a locating tool. Many engines, including Cat, Cummins etc drive their injector pump via a tapered shaft with no key at all, to facilitate timing. This is the reason why you do not grease the taper on a prop or coupling. They will likely come loose if you do.

Well, I've heard white lead should put on the shaft to make it so you could remove it someday. After all you do have a Key. Ask fastbottom about removing stuck props underwater.

[fstbttms]

Originally Posted by Chas Erwin

I always wonder how does FastBottoms do a well lapped propeller install?

I have installed many dozens of propellers underwater- fixed, feathering and folding. Hardly any of them have fallen off.