Propeller shaft key material
- Thread starter DArcy
- Start date
I have about 12” of bronze stock. I’d go with bronze. What size (width) do you need? If it’s the right size I’ll cut off a piece for you.
It should match the shaft, a SS key for a SS shaft, bronze for bronze.
Why wouldn't it match the prop, bronze for bronze? Or said a different way: why is it more important to match the shaft than the prop?
Good question. Keys are used, along with friction, to transmit torque from the shaft to the prop. If the key stock is softer than the shaft the constant application of torque will cause it to gradually wear. As it wears it will rotate within the key way and may eventually shear.
Shaft keys revisited
Dimensions of shaft keys, standardized many years ago, are commonly considered to be the main concern in applying these devices. However, designers tend to forget that other important...
I was told by a prop specialist that the key isn’t needed, if the taper is properly lapped and fit to the hub. It’s backup.Good question. Keys are used, along with friction, to transmit torque from the shaft to the prop. If the key stock is softer than the shaft the constant application of torque will cause it to gradually wear. As it wears it will rotate within the key way and may eventually shear.
Shaft keys revisited
Dimensions of shaft keys, standardized many years ago, are commonly considered to be the main concern in applying these devices. However, designers tend to forget that other important...www.machinedesign.com
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,746
@dlochner I understand that choice in association with a motor powering equipment on the shop floor.
But on a boat we are turning an expensive piece of hardware (the prop). If fitted properly the friction on the shaft maintains the prop in rotation. The key acts like a fuse to break should the prop contact something while the shaft continues spinning.
At the least that is my understanding.
But on a boat we are turning an expensive piece of hardware (the prop). If fitted properly the friction on the shaft maintains the prop in rotation. The key acts like a fuse to break should the prop contact something while the shaft continues spinning.
At the least that is my understanding.
I’ve never seen a key on a lathe. All held together by the Morse Taper.
It's interesting that the first linked article says the key should be the same strength and hardness as the shaft OR hub but the second article says the same strength and hardness as the shaft. The internet seems to be conflictedGood question. Keys are used, along with friction, to transmit torque from the shaft to the prop. If the key stock is softer than the shaft the constant application of torque will cause it to gradually wear. As it wears it will rotate within the key way and may eventually shear.
Shaft keys revisited
Dimensions of shaft keys, standardized many years ago, are commonly considered to be the main concern in applying these devices. However, designers tend to forget that other important...
My shaft is stainless and the prop is bronze. I will see if I can find 316 stainless 1/4" key stock.
And conflicting information on the internet is surprising?It's interesting that the first linked article says the key should be the same strength and hardness as the shaft OR hub but the second article says the same strength and hardness as the shaft. The internet seems to be conflicted
My shaft is stainless and the prop is bronze. I will see if I can find 316 stainless 1/4" key stock.
The design and shape seem to important rounded edges, no sharp corners.
Try McMaster-Carr or the Canadian equivalent for key stock.
Yea McMaster Carr is a great source, and I have used them often through work, but they don't ship to Canada for individuals, only businesses. I sail with a guy that runs a metal supply shop, and has supplied me with bronze key stock. I will check with him. Actually, he retired and his daughter and son in law run the shop now, but he is still involved with it. Some people don't know how to retire.
Stainless shaft, stainless key. Bronze shaft bronze key.
Anyone who says a key isn't necessary, isn't someone I'd ever do business with again.
The key is there because the prop nut isn't always as tight as you'd like if you want to get the cotter key through the nut, and as mentioned above, a breakaway in case your prop hits anything serious, not just to save the prop, but the transmission, motor mounts and possibly the engine. But you don't want it so weak (bronze in stainless) that it will break too easily.
Anyone who says a key isn't necessary, isn't someone I'd ever do business with again.
The key is there because the prop nut isn't always as tight as you'd like if you want to get the cotter key through the nut, and as mentioned above, a breakaway in case your prop hits anything serious, not just to save the prop, but the transmission, motor mounts and possibly the engine. But you don't want it so weak (bronze in stainless) that it will break too easily.
Interesting discussion about using the key as a safety device to save the drive train in a case of suddenly stopping the prop. My prop is very well protected so I'm not too worried about anything getting in there but I suppose it could happen. If that is the case however shouldn't we design to fail at a specific load? That got me thinking, what would the load on the key be? Fortunately, I'm a mechanical engineer so I just did a little math
The numbers above are for a Pathfinder model 50 with a 2.5:1 Hurth transmission. These calculations also assume the taper takes none of the torque, which is obviously not accurate.
It turns out, the bronze key is sufficient for my application and may actually be better if I am interested in protecting the drive train. A safety factor of 5.5 is plenty for ensuring the key will not shear under normal loads but may actually protect excessive loads from getting to the transmission.
This makes sense since there was a bronze key in there previously and it stood up just fine. I'm only replacing it because the previous prop had a wider key way so the key in there was machined down from a wider key to fit on the key way on the shaft. The prop I'm replacing with has the same size key way as the shaft.
The numbers above are for a Pathfinder model 50 with a 2.5:1 Hurth transmission. These calculations also assume the taper takes none of the torque, which is obviously not accurate.
It turns out, the bronze key is sufficient for my application and may actually be better if I am interested in protecting the drive train. A safety factor of 5.5 is plenty for ensuring the key will not shear under normal loads but may actually protect excessive loads from getting to the transmission.
This makes sense since there was a bronze key in there previously and it stood up just fine. I'm only replacing it because the previous prop had a wider key way so the key in there was machined down from a wider key to fit on the key way on the shaft. The prop I'm replacing with has the same size key way as the shaft.
Buck Algonquin is the manufacturer of almost all the shaft for recreation boat.
United Propellers (A dealer in Ontario, Canada) provided me with a new Aqualoy® 22 shaft with stainless keys. They lapped the propeller and flange for me.
www.unitedpropeller.ca
You must lap the key with the shaft and the propeller for proper fit.
Check this out for your safety.
United Propellers (A dealer in Ontario, Canada) provided me with a new Aqualoy® 22 shaft with stainless keys. They lapped the propeller and flange for me.
Shaft Failure Orillia | United Propeller
www.unitedpropeller.ca
You must lap the key with the shaft and the propeller for proper fit.
Check this out for your safety.
Lap Fitting A Prop To A Shaft
The process of lap fitting your prop to the prop shaft taper makes certainj both the shaft and prop mate together on the taper well with no high or low spots. When you see the inside of a prop with rings or high and low spots it was not reamed or lap fit properly. The mating of the two...
forums.sailboatowners.com
When I changed props on Sun Gypsy it took a large gear puller, a 3 foot Johnson bar and a large hammer to get the old prop off. I think I could have run for the next twenty years without the key or the nut however both went back on with the new prop. Really wouldn’t want to leave it on the bottom of the sea.
I have no idea of the puller you used, but every proper prop puller I've used was a bit springy and after tight, most often just hitting the bolt on the puller with a small sledge hammer, they just pop off. If that doesn't do it in a hit or two, heat the hub and I guaranty you that sucker will just pop right off of there.
So the weirdest thing about my situation (but not completely surprising considering some things I have found on this boat) is that the prop that came installed on the boat was for the wrong sized shaft. I didn't measure, it might be a 1-1/4" and I have a 1" shaft. Whoever installed it made a shim out of what appears to be PTFE. I was, to say the least, questioning this setup.
The previous owner said he thought the 3 bladed prop that was on there was a bit too big and gave me the original 2 bladed prop. I did find I could not get max RPM out of the engine and was not getting the same speed under power as other people with the same boat and engine. I am now very glad I decided to switch the prop, I don't know how long that shim would have held.
I'm guessing the PO got the 3 blade for a good deal and decided to try it.
Anyone want a 3 bladed 16x13 prop for a 1-1/4" (ish) shaft? I certainly have no use for it. Free shim included
I was, to say the least, questioning this setup.The previous owner said he thought the 3 bladed prop that was on there was a bit too big and gave me the original 2 bladed prop. I did find I could not get max RPM out of the engine and was not getting the same speed under power as other people with the same boat and engine. I am now very glad I decided to switch the prop, I don't know how long that shim would have held.
I'm guessing the PO got the 3 blade for a good deal and decided to try it.
Anyone want a 3 bladed 16x13 prop for a 1-1/4" (ish) shaft? I certainly have no use for it. Free shim included
@capta I agree 100% with a little heat, unfortunately I didn’t have my torch with me and I’m hard headed enough to want to do it myself.