Prop Shaft

[sangerdan]

Or if you have crush grinding on the c-less you reduce the diameter in increments and let it outfeed. Turning on its own diameter will lessen the chance of leaving the prop end too far out of whack. C-less will leave far fewer surface imperfections due to the actual cutting process and leave fewer areas for stress risers. I would imagine it was turned to reduce diameter, I guess I was looking at the way I would have done it for myself. If you're hanging a $2k prop on the end of a shaft this long do want everything leaning your way of is everything good enough. I'm not trying to stir the pot but most guys on these forums are not dealing with 250 horse 45 mph boats , spend 10k on polishing and powdercoat and have your prop shaft touched up on the neighbors 10" SouthBend lathe. Looking only to maybe spread a little knowledge and get some thinking going.

[SnoC653]

I'm with you there. I've been trying to get the understanding of these materials out there.
I think I've brought this up a couple times too but i don't know if anyone is understanding this idea:
1. If the "run out" of the taper is not held to a very close tolerance there will be a whipping effect of the prop with one ear pushing harder than the other, in turn loading one side of the shaft.
2. Or if both ears are not delivering equal forward thrust then the shaft is feeling the same load.
The second is why I like the idea of a CNC prop. This manufacturing process will give you the closest to each ear supplying equal forward thrust.

While it is always good to eliminate uneven loading, the prop will still create uneven thrust. Disturbances in the water flow from the strut, from compression against the hull, and especially the prop leaving and reentering the water all generate uneven loads.

As for leaving the shaft 1" at the ends, that would require a 1" strut and shaft log. It would seem that more gain would be achieved by reducing the contact area in these areas. I had a discussion about this recently when we were either turning down a 440 crank or boring the journals in the 400 block.

[sangerdan]

I like the idea of a nc'ed prop BUT in an ideal world it is the best solution. As someone who actually had a machine shop and was killed by the "digitizing" thing, the work will go overseas once that is done. Anyone with a co-ordinate machine can digitize; punch the button and you can have the code spit out the other end and onto your nc. No matter what you think you know about your product when some overseas company puts up an nc prop on Ebay your business is going in the shitter. Shops in the Phillipines were selling a piece on our shores for less than I could buy aluminum by the pound, before I touched it. If the Grose's are prop people and can do what Kindsvater or the other know and can do something is saved. If not hello foreign props. "Be careful what you wish for" means more today than ever.

[HB Vic]

I'm with you there. I've been trying to get the understanding of these materials out there.
I think I've brought this up a couple times too but i don't know if anyone is understanding this idea:
1. If the "run out" of the taper is not held to a very close tolerance there will be a whipping effect of the prop with one ear pushing harder than the other, in turn loading one side of the shaft.
2. Or if both ears are not delivering equal forward thrust then the shaft is feeling the same load.
The second is why I like the idea of a CNC prop. This manufacturing process will give you the closest to each ear supplying equal forward thrust.

Obviously the closer to perfect you can make anything the better off you'll be. But as you know, perfection isn't cheap. And since you're dealing with variables to begin with, does it really matter that much? Boats turn (normally lol) so that affects the loading on the prop. I'm sure the water conditions will also affect it.

The mass of such a small (relatively) prop spinning at fairly reasonable rpm most of the time, isn't all that great. If the prop was 10' in diameter and weighed 10,000lbs different story.

Not saying its ok to be sloppy, just saying perfection probably isn't necessary for 99% of the boats out there.

[ogshotgun]

Maybe, but keeping it set and hammered becomes more of a challenge.

I agree John Hart with dirty sanchez does pretty good in his ..

[sangerdan]

I need to clarify my previous post. I am a geographic undesirable in most of these talks : I don't know any of these people because I'm 2000 miles away. What usually gets lost is the craftsmanship and knowledge of the details when a product is nc'd. If I bought a prop that didn't quite work and needed it tweeked will it still fit the fixturing on the machine or will the shop that machined it have the ability to transform my arm waving and gesturing and non-tech words into what I need. I'll bet the old prop masters could, and that would be a shame to lose for the repeatability of an nc prop. When its a week between races and you want to try XorY don't call Manila or Bejing or increasingly HoChiMihn City or Jakarta.

[gn7]

This is what a 100% unfinished bar looks like. Your strut bushing would last about 1 revolution.
Attachment 39562

You could very well be dead on. I just know that I have never seen a shaft that had anything approaching the surface finish or the diameter accuracy of a crankshaft or even a rocker shaft from something like a FE or BB Mopar. Not saying it looked like hot rolled bar, just not something that looked "tight tolerance"

[HB Vic]

Yeah I agree, but it seems everyone spends endless amounts of time and money on the perfect engine and then almost no thought is put into that last line of propulsion.
But what is a reasonable RPM? If a flatty is running 7000 engine RPM with 50% overdriven in the v-drive the prop speed is 10,500 RPM. Would you run an out of balance, or out of round, or non concentric tool in one of your spindles at that speed? You know your spindle bearing wouldn't last very long.

Knowingly, no. But how often will that boat see 10,500? Just saying perfection probably isn't necessary. But damn close would be much better

[sangerdan]

Centerless ground finish on the size and material of a rocker shaft is easy. Grinding or machining high nickel, chrome and some other alloys is a bitch to do period. Getting a finish that doesn't look like a plowed field is either a lot of work or a lot of very specific experience. Rocker shafts are heat treated and not "gummy" like these shaft materials.

[HB Vic]

Pretty sure most the circle boats are seeing those RPM's at the prop most of the time. Not engine RPM, prop shaft RPM. Don't most of them run 50 over or somewhere close to it. Where's Bob?

It would be interesting to see what those shafts do in a hard turn