Shaft key SS or Bronze?

[Solstice]

I know this topic has many different opinions, so I thought I’d get your take. I’m installing a new prop and have both SS and bronze stock. Got the bronze from Hamilton and the SS came with the original prop out of the factory and have used both over the years.
I understand that the prevailing wisdom has been that the bronze will give before the drive train gets ruined, but since it’s a safety mechanism and the taper does all the work I’m wondering if this advice is still valid?
I would prefer to use the SS only because it seems to fit a bit better. I have chamfered the corners on the bronze and can work it to fit better but since I can go either way, I would appreciate your thoughts.
I did speak to a prop guy out of Rockland at the Maine Boatbuilders show last month and he said it really doesn’t matter??
Thanks as always!

 

[Rich Stidger]

If the stainless steel was supplied with the prop, I would use that.

 

[jssailem]

@Solstice I just went down this rode. I have a SS shaft, and a pretty brand new prop in bronze. I elected to get the key in bronze as well. The maker suggested bronze stock. It was available. I found that adjusting the key to the key slot with a light rasp was easy. Likely easier than if I had to adjust stainless steel. I lapped the shaft as recommended by @mainesail.
It was a smooth process.
The prop fitted nicely. We tightened the shaft nuts, stuck in a cotter pin and took her out for a spin.
All worked as hoped.

 

[Solstice]

Thanks jssailem. I also plan on lapping for the first time so it should be interesting. I’m a little nervous as I always am when doing something for the first time.
Rich, the SS stock came with the boat and original prop. I’m actually installing a new Gori to replace the factory fixed prop...

 

[jssailem]

Lapping was easy.
No 15 minute record set as suggested by @mainesail, but it was less than an hour.

Bought the prussian blue and lapping compound from NAPA. Have a hand full of rags, water and cleaning fluid available. Having no feel for the process we did the testing a couple of times. One needs to clean off all of the compound each time if your going to test fit. When cleaned up and fit the metal pieces were melded smoothly together. Threw the prussian Blue stained rags away. That stuff gets everywhere.

 

[Solstice]

Lapping was easy.
No 15 minute record set as suggested by @mainesail, but it was less than an hour.

Bought the prussian blue and lapping compound from NAPA. Have a hand full of rags, water and cleaning fluid available. Having no feel for the process we did the testing a couple of times. One needs to clean off all of the compound each time if your going to test fit. When cleaned up and fit the metal pieces were melded smoothly together. Threw the prussian Blue stained rags away. That stuff gets everywhere.

Thanks for the encouragement! I have the clover grinding compound as in MS pictorial. I am planning on skipping the Prussian blue step as several machinists told me that I can just use the banding that the compound will show.
I also saw a You tube video showing someone using a thick blue sharpie in a pinch. Unfortunately none of the NAPA stores in my area carry the PB.
Do you have a sense on how many turns it took to get your prop lapped to your satisfaction? I know they will all be different...
Thanks again!

 

[jssailem]

I would guess about 30. We tried the 15-20 identifed by Mainesail, but when we did the prussian blue test - not satisfied. So we went at it another 10-15 and found ready to close.

 

[rgranger]

@Solstice I just went down this rode. (snip)...

@jssailem
Hahaha.... was that Freudian or intentional.

 

[Charles Erwin]

I have chamfered the corners on the bronze and can work it to fit better but since I can go either way, I would appreciate your thoughts.

Some thoughts:

1) See to it the key stock sides in the propeller key way but fits firm and snug in the shaft key way.
2) Put the prop on (without the key) then mark where the prop stops moving forward on the shaft. That way when you put the key in for the final assembly you will know the key does not migrate forward thus messing up your lapped fit. The key material is not very important by the way.
3) If you have a two shaft nuts that lock against one another put the thin nut on first.

Charles