Flexible coupling

Nasher · 11 January 2015, 18:40

Sorry, this isn't RIB related, but I'm sure there will be people on here with an opinion.

The little project I'm working on at the moment involves a small inboard engine and shaft drive prop.

I've never had the engine fitted to the boat so have no original fittings.

I've sourced some aluminium to machine up a flexible coupling, and will be aligning the engine output shaft and prop shaft really well.

However today when looking at it I had a thought.

The propshaft and engine output shaft are only 5/8in in diameter.
The engine itself is very low power and torque, a 4.5HP 2-stroke, and it will drive a small 8x7 prop.

So the thought occurred, that considering the low torque/HP, and the good alignment I'll achieve, why don't I just join the two shafts with a length of thick wall rubber hose pushed over and clamped to each shaft with a small gap between the shafts inside the hose.

What do you think?
Would it last very long?
Am I being daft?

Nasher.

Nos4r2 · 11 January 2015, 22:11

No, not daft.
I'd have some form of flexi coupling in there if I could. Hose or a rubber doughnut would be my first go-to.

beamishken · 11 January 2015, 22:31

A steering column uj from a breakers yard should work fine just need to find one roughly the right size & maybe bore out the splines but at 5/8 dia you should be in the right ball park might be more robust than a hose & clips

Pete7 · 12 January 2015, 08:18

Nasher, I thought drive shafts were offset slightly to make the UJ joint work properly as a joint. If they are in a straight line it causes problems with wear and vibration.

A steering UJ is a good idea and would look like a proper bit of engineering. Have to be a landie one though

Pete

Nasher · 12 January 2015, 11:31

Quote:

Originally Posted by Pete7

A steering UJ is a good idea and would look like a proper bit of engineering. Have to be a landie one though

Pete

Pete Hi.

Yep, good idea by Beamishken, I'm thinking of:
NTC3486 Genuine Land Rover Range Rover Flexible Steering Coupling | eBay

As far as I'm aware a UJ(Universal Joint) needs to be slightly at an angle, but a CV Joint(Constant velocity Joint) can work straight.
Might have that the wrong war round though.

Nasher.

Nasher · 25 January 2015, 17:15

Been thinking about this some more today having managed to get a couple of hours to myself.

The ideal solution appears to be a rubber doughnut type coupling exactly like the Hillman imp one hanging on my garage wall, but unfortunately it's too large in diameter.

Thinking about Beamishken/Pete7s suggestion, it appears Range Rovers have a similar thing in their steering column, but I'm not sure how it would stand up to constant rotation.
See Imp one and RR Steering one below.

So a question for those of you who've played with different types of Cars, Bikes etc over the years - What's the smallest Rubber Doughnut type coupling you've come across?

Nos4r2, I'm expecting you to mention the Ural one

Nasher.

Nos4r2 · 25 January 2015, 21:52

Never owned a Urinal.

I wonder... there's a rubber cush drive in one of the old GS wheels I have lying around.

doggypaddle · 26 January 2015, 11:51

Multispiral Hydraulic hose will do the job really well, especially if use 2 bolt type band clamps each end 180 degrees rotated to keep it in balance.
a piece of hose will allow slight radial and axial miss alignment and is actually a really good constant velocity joint.
a Hooke type UJ will only allow axial miss alignment and not radial, and then it will vibrate as its nor a constant velocity joint. If you have a UJ driving through an angle (like a prop shaft on a car) you need two at equal angles with the yolks rotated 90 degrees to end up with constant velocity at the output.
Rag joints are quite forgiving and there's some smallish ones on Daihatsu and Toyota steering columns and land rover slightly larger as you already know. I have some small Ujs but at 1/4 inch shaft too small I think.
you probably already thought of this but most joints will not take any thrust without vibrating badly or breaking.
personally I would try hydraulic hose(we use it in work on an automotive dynamometer 2" and it lasts!!) or landrover steering UJs (cheap and plentiful)

Nasher · 27 January 2015, 13:21

Thanks Nos and Doggy.

Think I'll get hold of a Rangie one as above to see what it's like, but really like the idea of the simple bit of hose.

I'll try to get a piece of what you suggest in a @5/8'ID, double up the clamps and spread them around for balance, and put a spare bit in the boat just in case.
Or if I can only get larger I'll machine up some sleeves for the shafts.

It will be a while before it's ready to go anyway.

Nasher.

Nasher · 27 January 2015, 13:31

Thought I'd put some pictures up of what I'm up to.

1940's Mk9 Military canoe that I've owned for 30yrs, and while it's been at the National Maritime Museum in Falmouth for a few years I've sourced the correct engine. It's believed to be the last Mk9 around.
There is a book on the whole series developed from the Mk1 Cockleshell Heroes Canoes.
The guy who wrote the book on them used mine for a lot of reference photos.
http://www.amazon.co.uk/The-Cocklesh.../dp/1848680651

Images 1, 2 and 3 are the boat itself. Image 3 is obviously a historic image from the NMM Archives.
Image 4 is a historic image of the engine in the boat.

Nasher · 27 January 2015, 13:34

Image 5 - The engine

Image 6 - The engine bay

Image 7 - One in T'other

Image 8 - The joint I need to make

doggypaddle · 27 January 2015, 17:58

Given that you already have one flange cant you machine up an identical one, and make the middle bit out of a piece of conveyor belt?
That would look like original maybe,
I used to have a few rag joints hanging around like that, off ww2 generators with villiers engines. they went in the skip a long time ago though.
I seem to recall some of these joints had steel centres with small rubber bushes for the pins to locate in.

you could just buy one of these though

5/8" L075 Flexible 3-Piece L-Jaw Coupling Coupler Set & Buna-N NBR Rubber Spider | eBay

doggypaddle · 27 January 2015, 18:08

https://sdp-si.com/eStore/Catalog/Group/984

this place has them in the UK.

Nasher · 27 January 2015, 18:40

DP

Unfortunately the flange on the output shaft is one I found locally and doesn't actually fit very well.
I brought it for a couple of quid as a 5/8 bore, and thought I'd been had when it had too bigger hole.

However I've had a better chance to have a measure up this afternoon and have now realised the propshaft is 5/8in, but the output shaft on the engine is 19/32in.

I could machine up two flanges of course, and either incorporate a small doughnut or something along the lines of your ebay link, but I'm really tempted to try some -10 Hydraulic hose which has a bore of 15.2mm or 5/8in with 4 clamps. It certainly looks and sounds like the easy/lazy way out.

I'll have a think about it, as I still need to source or machine up a stuffing box/shaft seal because I can't find one smaller than 1in at the moment.

If I have to sleeve the propshaft for that it will effect what I do with the coupling too.

All good fun, my trouble is having to go to work gets in the way.

Nasher.

doggypaddle · 27 January 2015, 19:53

I think a hydraulic hose will do the job, especially with a few Mikalor type clamps, After all there cant be much torque there if you've only got a few HP.
assuming you have your power at 3000rpm that's only 8Nm
it would certainly get you up an running.

Nos4r2 · 27 January 2015, 23:18

What is that on the joint in the original pic? Is it a bit of hose and jubilee clips being used as a grease seal and 2 nuts to push grease in?

doggypaddle · 28 January 2015, 08:12

It looks like the stuffing box is held onto the stern-tube with a short length of hose and a few jubilee clips doesn't it. and as you say there's the standard two bolt flange on the stuffing box to compress the Hemp/Horse hair and grease. The rag joint is just visible under the tank.