Shaft couper solutions/recommendations

They are the standard on most CNCs and they work great. The load on the grub screws is huge though. All the force is concentrated on the screw tip. I like the clamping collar style more.

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It has both - clamping and fixing by screw. The screws for the clamp is on the other side.

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I am not sure, but is the thrust transmitted through the coupling to the thrust bearing or is this thrust bearing for braking only?

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I have this same coupler, untested also. Do you have more photos of your setup? Is that groove for a face seal O-Ring?

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Only for forward motion. For reverse there is a slight chance that the coupling will be pulled apart.

I will post my setup soon!

Do you have 2x ball bearings (with some distance between) behind the jaw coupling? The dual setup with distance is important to prevent leaks in the shaft seal, due to wobbeling in the shaft.

A notch on the shaft between the two bearings can take thrust into the deep groove bearing (they can take quite a bit with regular service life).

See attached cross section on how we solved it with a jaw coupling. :slight_smile:
Nikolai

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Was the reason for doing this because the jaw coupling can’t take the axial thrust loading or just to remove the thrust bearing? Is a simple solution if you can get the shaft machined and the bearing can take axial load.

The jaw coupling is not made to take axial loads (at least we think so:p). So yes that was one of the reasons. And it will also take away the need for a thrust bearing.

We calculated the bearings, it should be just fine.

That’s my coupler history (from left to right)

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So which one would you recommend? I had a discussion with a friend who is a mechanical engineer with experience in that field. He recommended a clamp style coupler, not one with set screws, best would be one with 2 screws on each side for max strength, but this increases the length. Also he recommended to use two bearings on the shaft so this would match with Hiorts brothers drawing above. My friend also suggested to invest in a machined part (with a lathe) because with 3000 rpms, the shaft needs to be perfectly aligned to run true.

Straight couplers are pretty much useless. No shaft is perfectly straight. This would cause binding.

My experience with clamping only the shafts is that I had to dissamble my whole pod at the beach (like at least 3 times) because it always got loose (shaft was not clamped anymore because the torque is way too high). Even with lock tide and a high screw tightening torque it wasn’t possible.

A combination of both is in my opinion the best option. I also have an additional bearing so it’s a need for having a flexible coupling.

I recommend the jaw coupling with two threads for set screws and a shaft with a flat spot.

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Update:
The Jaw Coupler failed today as well:

@Hiorth: How much torque does your setup has, roughly?

The next one I will test is this one (for max. 10Nm):

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Apx 10-12nm you need a spider that can handle sufficient torque.

Can you provide a link, please?

Check maedler.de Thats a good german shop for everything transmission.

25 x 98 shore

max torque from motor with gearbox is probably 8-10nm.

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Thanks Hiorth! I didn’t expect that the coupling will be such a problem. Good ride!

Just to confirm this a second time:


As you have stated before those spiral couplings can‘t handle the torque. I used it until my elastic star coupling arrives. It failed after a few hours of testing in my jet drive with max 3.6Nm. It took only a small leaf through the impeller to finally break it.

This one can handle 15 Nm