Re-installing the shaft coupling
- Thread starter Straycat22296
- Start date
Won’t hurt but anti-seize might be better
Use the correct compound best suited to the specific metal - Anti-Seize Brochure - ROCOL
Use the correct compound best suited to the specific metal - Anti-Seize Brochure - ROCOL
Might have to blame that one on spell check. I try to review posts and still some get by. I should turn it off but I'm not a good speller to begin with. In fact, when in spelling Bees I knew I'd have an early lunch - which suited me.
You do not want to apply any anti-seize, lubricant, etc. to your shaft coupling. You want that coupling to seize together with the shaft.
Friction between the coupling and the shaft is important, it takes the stress off the key and makes for more efficient energy transmission from the engine to the shaft. Do not use and lubricant or antiseize on the shaft or bolts.
Replace the coupling with a split coupling and in saltwater spray after installing the coupling on the shaft and transmission coat the coupling with an anti corrosion spray like CRC Anti-corrosion spray (Amazon link). The coupling will slide on easily and the bolts will clamp it down to the shaft.
Here's an example:
www.fisheriessupply.com
Replace the coupling with a split coupling and in saltwater spray after installing the coupling on the shaft and transmission coat the coupling with an anti corrosion spray like CRC Anti-corrosion spray (Amazon link). The coupling will slide on easily and the bolts will clamp it down to the shaft.
Here's an example:
ZF Split Shaft Couplings - Buck Algonquin | Fisheries Supply
Save More on Your Buck Algonquin ZF Split Shaft Couplings at Fisheries Supply. Excellent Customer Service, Ready to Ship. Marine Supplies Since 1928!
www.fisheriessupply.com
If you're relying on the parts to seize together for strength, you're in the wrong business.
If the shaft key and set screws don't give you a factor of safety of 20+, it's time to dump the whole assembly and start again.
Don't make life impossible for the next poor guy (it may even be you) who has to take the flange(s) off. This is the first sign of a good millwright.
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I have always added an anti-seize to shaft / coupling as well as prop. As was said, the bolts and key are the components to hold it together, not the metals seizing together. Been doing this for the past 20 years and never had an issue so I will continue so I have an easier chance to remove next time. It encourages maintenance knowing its not going to be an issue to remove.
Some people actually have to work for a living.It looks like the OP is a ghost
(poor souls) It's only been 14 hours since he posted. We'll give him some time.
Honestly, straight couplings are not a great system IMO. That's why they're used on low horsepower applications. From an engineering perspective, I totally agree with you; but that's not really how a straight coupling works. I upgraded to a Sigmadrive reason for this reason. I found the "engineering" of a straight coupling lacking.
In a straight coupling, the coupling is precision machined for a slight interference fit with the shaft. When you buy a coupling, it is machined to be mated with the individual shaft it will be paired with. The problem is that when you throw life (wear, corrosion, stress, taking the coupling on and off etc.) into the equation, that interference fit can loosen up quickly and you end up with the fit being too loose. The key and the set screw end up taking the torque load instead of the interference fit as intended. The slotted key and the set screw are not designed for this,. They are supposed to be a safety measure. Again, in my opinion, the engineering on this kind of coupling really isn't great. It's kind of a cheap "belt and suspenders" way to do a shaft coupling for a low horsepower application. It's not a system that's conducive to maintenance. Once the coupling siezes to the shaft, it can go years and years and work great. When you start talking about removing the coupling for maintenance, problems can start.
You can make the argument that some kind of lubricant, anti-seize, whatever will help the corrosion issue, but ultimately you're taking away from the capacity of the coupling to transfer torque to the shaft.
I did a lot of research on this subject. I'll try to find the write up that I found on how these coupling are intended to work to post (I found it, it's attached). Ultimately, I wasn't satisfied with the robustness of straight coupling systems, so I upgraded to a Brunton's Sigmadrive. The Sigmadrive uses a precision taper system to clamp down on the shaft. The design was inspired by work that the inventor did on ice breaking vessel shafts (they use a hydraulic clamping system). It's much more robust. Even so, the instructions from Brunton's recommend nothing more than a light lubricant on the tapered area within the Sigmadrive (to aid the clamping process) and no lubricant on the area that mates directly onto the shaft.
Regardless, if the coupling is fit to the prop shaft correctly, you'll never be able to pull it off easily without a coupling/flange puller. If you want to stay with the straight coupling system, I definitely suggest picking one up to allow you to safely remove the coupling when it's seized on the shaft.
Buck Algonquin 5 inch 50MCP00500 Flange Puller
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The OP's question dealt with anti-seize on a straight coupling. FULL STOP. Nothing about coupling construction.
Statements like this from your linked article do nothing to clarify the situation :
No thought about how an interference fitting does in fact go together with anti-seize between the surfaces if the same anti-seize is supposed to keep these same surfaces even further apart. Something wrong with the thought process here.
And looking at typical sailboat shaft couplings, and using your "engineering perspective" I am more than satisfied that a properly fitted straight coupling is more that adequate to absorb the applied torque without coming loose.
And finally, I know you'll want to retract this when you read it again :
Statements like this from your linked article do nothing to clarify the situation :
No thought about how an interference fitting does in fact go together with anti-seize between the surfaces if the same anti-seize is supposed to keep these same surfaces even further apart. Something wrong with the thought process here.
That statement is going to take one hell of a pile of analysis to convince me how the shear strength of a shaft key is going to be reduced by introducing a contact surface of anti-sieze.
To use your words, if I may, spending a good portion of my life in refineries looking over the shoulders of people working on these couplings up to 100 HP revealed how the professionals do it. Tight fittings on these couplings DO NOT FAIL.
And looking at typical sailboat shaft couplings, and using your "engineering perspective" I am more than satisfied that a properly fitted straight coupling is more that adequate to absorb the applied torque without coming loose.
And finally, I know you'll want to retract this when you read it again :
Care to calculate the opposing torque due to the shaft key in shear compared to the frictional shear force of the "seized shaft?"
Interference fits are a very acceptable means to transmit power through shafts. I'm not arguing against that. My main point is, in this particular application (a recreational sailboat), there are better ways to accomplish this, and that if you're going to use the straight-shaft system, it's best to keep anti-seize out of the equation when you're fitting the coupling back on the shaft. I'm also saying that, in my opinion, the system isn't really all that robust for this application, and it's best to leave it alone and let it seize together. Use a flange puller like the one I linked above to get it off again next time around and it will work out.
In an industrial setting where professionals are looking after the maintenance, it's not sitting in humid salty air, professionals are bringing special tools to bear, have better access for maintenance (presumably), and they're not out on an island somewhere, there's nothing wrong with interference-fit torque transfer.
Here's a whole article about interference fit torque transfer. Pretty neat. It can be very, very strong.
https://theengineeringblog.com/shrink-fit-interference-torque-torque
It's not really the strength of the shaft key safety connection that that's the issue. I have no doubt that if you hooked up an oversized coupling loose on the shaft and measured the breaking force of the key/screw connection, it would be plenty strong to transmit the torque you're asking it to take. The problem is more along the lines of the forward-reverse-forward (sometimes rapidly one after the other) that the connection sees, as well as the associated forces with pushing the boat forward and pulling it backwards. The key/set screw can work itself loose over time; the press-fit connection is the connection that can take these forces. It's just not great practice to put anti-seize between the two mating surfaces that you are relying on friction for to get the job done.
If the press-fit/interference-fit isn't on point, the screw/shear key safety situation isn't really designed to take the forces I'm describing above for an extended period of time. I've seen it happen and it's a total PITA to fix because the boat has to be pulled out of the water in order for a new coupling to be custom-machined to the propeller shaft in question. The shaft has to come in to the machine shop with the flange so that it can be precision fit.
The shaft/screw connection is there as a safety so that the propeller shaft doesn't fall out of the boat and you can get yourself home.
If all things are right dimension-wise with the connection, my guess is that putting anti-seize on the shaft won't cause the connection to break free, but it's not really best practice to do so. I don't think I'm going to change your mind that you should or shouldn't use anti-seize to put the connection back together, but that's cool. I'm glad that the system you have works for you.
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Thank you for all the information and opinions.
This is why I enjoy this site so much.
I will have to mull over the information and then decide how I wish to proceed.
This is why I enjoy this site so much.
I will have to mull over the information and then decide how I wish to proceed.
Do you
2. Can you have the interference fit flange assembled in a shop and then fit into a sailboat ?
1 ANS : An interference fitting requires large forces only applicable with a press. Or thermally fit. What we have in a sailboat is just a good snug fit, easily installed with a screw device.
2. ANS: You can figure that one for yourself.
And that's why it's done the way it's done because THAT'S ALL THAT'S REQUIRED FOR A SAILBOAT.
Now, if your designing something for the Space Station, that's something else.
1. Do you know what an interference fitting is ?
2. Can you have the interference fit flange assembled in a shop and then fit into a sailboat ?
1 ANS : An interference fitting requires large forces only applicable with a press. Or thermally fit. What we have in a sailboat is just a good snug fit, easily installed with a screw device.
2. ANS: You can figure that one for yourself.
And that's why it's done the way it's done because THAT'S ALL THAT'S REQUIRED FOR A SAILBOAT.
Now, if your designing something for the Space Station, that's something else.
I put a little Lanocote on the shaft and coupling when I last removed the coupling to install a Volvo shaft seal.
No issues with anything slipping, and I hope it makes separating the coupling and shaft a little easier in the future.
If I ever have to replace the coupling again, I will use a split coupling.
But for now, it is fine.
Greg
No issues with anything slipping, and I hope it makes separating the coupling and shaft a little easier in the future.
If I ever have to replace the coupling again, I will use a split coupling.
But for now, it is fine.
Greg
