Key Material for Bronze Prop

[fstbttms]

Originally Posted by never monday

Props and shafting are machined to an indusrty standard. There for if every reputable shaft and prop builder uses this standard, then all the tapers are the same.

In therory, maybe. But in the real world if you take 3 similar props from different manufacturers and mount them one at a time on a prop shaft, two of them will end up at different points on that shaft. Further, read the installation instructions for a high-end feathering prop. I can name at least two manufacturers that have provisions in their instructions for what to do in case the prop rides too far up the shaft (ie: cutting down the threaded end.) If all shafts and tapers were identical, this would be unnecessary.

[never monday]

If manufactorers are building things not to spec, then they are wrong. SAE and A.B.Y.C. both state how this should be performed.

[fstbttms]

Originally Posted by never monday

If manufactorers are building things not to spec, then they are wrong. SAE and A.B.Y.C. both state how this should be performed.

I can't speak to that although you are undoubtably right. I just know what I see every single day in the boat maintenance biz.

[Alan Wheeler]

Hang about, we are confusing two very different diamensions here. The diameter of the hole/shaft and the angle/pitch of the taper. The point at where a prop slides to on a shaft is determined by the diameter of the hole. The issue with a taper fit is that even a fraction of difference in diameter can account for a very different position the prop will come to on the shaft. The issue that we are talking about is to do with the mating tolerance of the taper. Both shaft and prop taper must be exact or big big problems will occur. This is an industry standard taper measured in degrees of angle. If the two are different,the mating surfaces will not be over the entire mating area which will mean the power from shaft to prop is not sent to the prop correctly, the prop will never sit dynamicaly balanced on the shaft and you can all imagine the possible results.
Because of the taper angle, when the two surfaces mate, the suirface actually comes together as as if it was two flat plates being samwedged together. The grease acts hydraulicly and stops the plates from mating perfectly. If the taper was slightly different between the two surfaces, then one point along the shaft will mate before another and the grease has a point of escape as it is being squeezed along.
ummmm, I don't know if I made that clear, did it make sense????

[SkiprJohn]

Alan, you made perfect sense. I need to do something to make the prop and shaft fit a bit better. Hub fits tight at the forward end before the aft before tightening the prop nut. There is a slight bit of wobble when on hand tight. I'm hoping to get the wobble out by doing some lapping with fine grit.

Do you ever use a product called something like anti-sieze or never-sieze?

JohnL

[DeepFrz]

Perhaps someone can answer a couple of questions that I keep asking myself as a read this topic.

What are the tolerances?

Are European specifications the same?

Also, I find it hard to believe that a thin layer of grease or anti sieze would cause a problem if all the components (shaft, prop, key, and groove) are all within spec. I would think that properly torqueing the prop nut would seat everything just fine and any unneeded grease would squeeze out leaving just a film to prevent galling. Am I wrong?

Deep.

[mike d.]

my first boat a stink potter with twins had bronze on bronze with naval brass keys on the way up from Westerly R.I. one of the props got free play took the boat to Melvilles now Hood/Hinckley middletown R.I. pulled the boat found the prob to be the key and way they gave me a key that fit the shaft and i had to file the key way on the prop to match i know this is improper way to do this but it got us home to N.H. border. pulled boat for season had shafts and props sized @ H@H never had prob after i was always taught that the fit was to be snug on the taper you ahd to use a puller to serperate to two. yo ushould not have to crank down on the first nut to get to prop to seat. ?! we always fit and put on dry.?!
regards mike

[Alan Wheeler]

Deep, yeah you are wrong, eehhh that sounds so harsh. It is the EP strength of greases. The very thin film can withstand many tons of pressure without going anywhere.
Actually as a side topic here, you can test the quality of grease by a very simple test. Place a small dab of grease on a flat slab of steel and then smack the grease with a hammer. Good grease will remain under the hammer head and poor grease will splat everywhere. Try it, it is fun.
Anyways, the film on the shaft eventually works out and the prop is loose on the shaft again. Remember we are talking a tolerance so small, it's just a smear of grease.

[fstbttms]

Monday, I will call my local prop shop (Bay Propellor in Alameda, CA. They do everything from 12" pleasure craft props to the really, really big 5 and 6-blade jobs found on big tugs and such.) I will ask them what, if anything, they recommend using to prevent galling and will report same back here.

[DeepFrz]

Wheels, thanks for the reply. Great information.

Deep

[delmarrey]

that might be useful to some. if this is not readable just send me a PM with your e-mail and I'll forward on you a copy at 4 X's this one. It's just too big to upload on the forum.



Sorry I don't have the metric version.................._/)

BTW For every .001" off on the diameter, the hub would move .016" (1/64") farther on/off the shaft.

All dim's are in 3 place decimal's which means they should not be off by more then + or - .005" by machine standards unless otherwise stated, which they are not on this chart. Which also means that the hub can not be out of position by more then .080" (5/64") either way. Better the hub be too small or shaft too big then visa versa.


A mis-match in tapers would be due to the skill level of the person doing the job. And I can say from EXPERIENCE that a lot of marine machine shops out there do not use precise (sine bar) methods of setting the taper on their machines. A shop that specializes in shafting and hubs I would trust more then the general marine yards.

[BBill]

It seems to me the key should be no harder than the softest material. If a bronze prop is used the key should be bronze no matter what the shaft material is. Damage of the more expensive part is less likely. Also, decades ago, the shaft, key and props were always bronze. The ONLY reason SS came into the picture (in the 1970s)was when it became cheaper than bronze.

I agree with fstbttms. What you see in the field isn't exactly what is written as spec. I use lube, pro dealers use lube, nobody has prop problems with it. I've changed dozens of props, shafts, keys in 40+ yrs of boating. Many new installations require the key to be filed to match the keyway for a perfect fit. Machining tolerances aren't that exact 100% of the time. This is standard operating practice at the largest and most credible engine dealers on high end yachts. It works without question. Google and ask them.

[Alan Wheeler]

Woooow up. Hang about BBill, we aren't talking about the accuracy of the key. The exact tolerance of the key is not the issue.
It's the shaft/prop taper we are stating MUST BE exact in it's machining. 100% exact. I think you would agree with that. The exact tolerance of the taper and fit between shaft and prop is and has to be spot on. I really don't care what other experts (and I would have to say "so called experts ")if they don't get that fit right, do or say. We have all heard of stories of the "credible" making mince meat of jobs. Speaking as a qualified engineer and I am confident Del will agree with me here, there is no room for era of the angle of that taper. There can be slight era in the diameter which results in the prop sitting at a different point of the shaft, but there can be no era in the taper angle.
Now, as an engineer, I am suggesting that you use gease or any "anti-sieze" very sparingly. Wipe it on and wipe it off. It requires very little to do the job and to much of a flim, I REPEAT, will stop the mating of the prop tpaer onto the shaft taper. If you don't want to believe that, well that's upto you, but this is my suggestion from an engineering point of view.

[delmarrey]

The angle up to 6" shafts is 3/4" per ft. (1 deg. 47' 24") on the dia.. Over 6" shafts the taper goes up to 1" per ft. (2 deg. 23' 9").

Mostly the keyways are for is alignment and back up in case there is a misfit but only for a short period of time. The key does not do the work but is there in the case of a hit to keep the prop from spinning on the shaft. They can be loose or tight within reason but do not take the load. The taper is suppose to lock in and do the work just like on a drill press, which in fact is the same taper (Morse Taper). If one shears a key they're going to need a new prop and probably a shaft as well........._/)

[Alan Wheeler]

Arrrrr, I wondered if it was a Morse taper.