View Full Version : Shaft Friction

03-18-2010, 09:39 AM
A few weeks ago a friend of mine contacted mo to help with a job he was biding on. Part of project was to place into service waterwheel that has been Idle for several years and never used. There are several issues that need addressed but the one that is bugging me currently is that of power transmission from; the wheel to the shaft and from the shaft to the additional equipment. The issue is: the wheel shaft is not keyed.
Wheel speed is only about 10 rpm but we think we will be producing about 8 hp. So that is a lot of torque. Shaft Dia. is 3 7/16. The wheel is attached to the shaft with a split coupling that is clamped around the shaft much like a split collar. so I am concerned about slippage between the wheel coupling and the shaft and also on the output end of the shaft where I attach a pulley for power transmission. The outboard end of the shaft is not keyed either so I must "clamp" to the shaft also. Welding is out of the question. wheel/shaft dissemble is not an option.
Has anyone had any experience increasing the friction of a power coupling by device; wrapping a shaft with aluminum oxide paper (sand Paper) and clamping around that with couplings, bushings etc. IF so what is your guess as to the benefit? Or I am open to other suggestions as to how keep my device from slipping on the shaft.

03-18-2010, 09:44 AM
You could easily grind a small flat with an angle grinder for a set screw or two.

With skill, paitence and much test fiting, you can key a shaft using just an angle grinder and files (Well, technicaly just files, but the angle grinder should really speed up the roughing out)

a touch of loctite might help too.

03-18-2010, 10:05 AM

Could you drill a hole through the collar and the shaft and put a bolt through it?


03-18-2010, 10:09 AM
You can also key a wheel to a shaft with a round pin. Drill in from the end of the shaft and parallel to the shaft where the collar and the shaft meet. and then drive the round pin in the hole. May notr be as nice as a square key, but that's how they did it before square keys.

Have you done anything like lock the shaft and then load the wheel to see if it slips? Those taper locks can exert a trmendous clamping force on a shaft. If necesary you can tighten the taper collar, smack it a few times with a hammer and tighten it some more. Even more clamping force.

03-18-2010, 12:13 PM
The proper way to do it is with a split taper sheave. It can provide enough clamping force on the shaft to run without a key.


03-18-2010, 02:14 PM
If you really see 8 hp @ 10 rpm, that's only 4200 foot lbs. I say only because you have a nearly 3.5" shaft to work with. ;)

There are bushings out there 3-7/16" diameter that can transmit 3 times what you need. If you've got an appropriately sized split taper bushing, I wouldn't worry about keying anything.

The Artful Bodger
03-18-2010, 02:23 PM
Sounds like a case for wash, rinse and Loctite!

If you go for kf2qd's pin in the end of the shaft you can tap the hole and screw a bolt in.

03-18-2010, 02:29 PM
It ain't never gunna slip.
No need for a key.
I've worked on stuff in grain elevators with a similar situation.
Sounds like no problem.


03-18-2010, 02:39 PM
Evan is right on the mark with the taper sleeve.
However, given the numbers involved, you could do a quick "check"
based on what the fasteners can do for you -- I imagine you have
two bolts holding the split collar together?

Check out the charts (online, etc) for bolt clamping forces. Torque
them properly and you'll get a good bite on that shaft (assuming there
is enough clearance between the split hub that it doesn't bottom out when

Go to a larger fastener (which might mean a beefier hub) if you want
higher clamping forces.


03-18-2010, 02:49 PM
It ain't never gunna slip.
No need for a key.
I've worked on stuff in grain elevators with a similar situation.
Sounds like no problem.


I agree. No way that thing is going to slip.

03-18-2010, 03:01 PM
Another one for Taper-Loc, but you say it's in situ and hasn't been run, so you need to check the condition of the shaft and existing bolted clamp.

Regards Ian.

03-18-2010, 04:16 PM
How about a taper pin, maybe #7 or #8?

03-18-2010, 04:47 PM
Thank you for the inputs.
I think a tapered bushing in a hub would be perfect except, I can't get access to the ends of the shaft to allow sliding a solid ring over the shaft.
I am now thinking along the lines of a split flanged collar/coupling that I could place on each inboard side of the wheel and clamp over the shaft with bolts perpendicular to the shaft to clamp it to the shaft and bolts thru the flange to attach to the Water Wheel. Maybe with a long enough coupling and enough bolts it should hold. Does anyone know of a manufacturer tho makes such a product? I'm afraid my 10" SB isn't the right machine for the job.

03-18-2010, 05:00 PM
Your getting carried away with something that will never cause a problem. When you clamp the split collar down on the shaft it will NEVER slip. Your not going to see a shock load on the water wheel and shaft nor will there be a shock load on the output side. I doubt that any water wheels used a key in the shaft. Some water wheels use wood bearings.

Was the water wheel made by a factory or an individual?

03-18-2010, 05:24 PM
It is estimated the wheel will produce about 5300 Ft. Lbs. of torque when running.

03-18-2010, 06:47 PM
Make two pieces on your SB like this:

It's a .5" thick disk with a 4.5" hole, OD whatever you need it to be. Cut out the ends with a band saw and put them as shown. Assemble the stack to make a sheave that is your OD with 4.5" ID hole and 1" thick. Clamp it together and drill a few holes, then bolt the works together. Punch some witness marks so you can put it together the same way after machining. Chuck it up on the ID and clean up the OD. Hold on the OD and run in a slight taper of no more than a couple degrees using the compound on the ID.

Make a matching taper sleeve with collar and proper shaft ID and index six bolt holes around the collar, then cut it in half. The ID of the sleeve should be the same as the OD of the shaft but the max OD of the taper of the split sleeve should be slightly larger than the Max ID of the taper in the Sheave. Make the holes in the collar slightly over bolt size.

Stick it all together and bolt it up tight on a mandrel, then turn up the OD to look like whatever you need for a sheave. You have room for a couple of Vee belts or good wide serpentine. Put it together on the water wheel shaft with some bits of cardboard in the gaps and the belts will never know there were gaps there.


Personally I would have the local job shop cut the discs for me with their plasma cutter.

03-18-2010, 08:21 PM
It is estimated the wheel will produce about 5300 Ft. Lbs. of torque when running.

Still not going to slip. Look at all the line shaft stuff out there. That stuff is not keyed and it transfers a whole lot more torque than your water wheel.

Jim Molloy
03-18-2010, 08:33 PM
Current Marine practice uses friction fit couplings to transmit power from engine to propeller shaft, no keys. These use hydraulic pressure to expand coupling to fit and remove, they transmit thousands of horse power to the blades and don't slip.
Jim M

03-18-2010, 09:22 PM
I'd go with a split flanged bushing or any one of the similar solutions. I would tend to stay away from a key or a cross bolt- there is a lot of torque there as has been figured, and you don't want to shear anything and/or trap pieces and make it a bitch to replace parts.

You might in fact want something to slip to prevent damage in case the shaft jams for any reason. Some slippage would be better than ripping the hub out of your water wheel.

I have to agree with others- even a fairly mild clamping arrangement, like a few muffler clamps for instance, is going to be able to create enough friction on a split bushing to transfer a lot of torque.

I'd guess you'd be looking to keep it all as rust-proof as possible, so that will dictate your choice of materials.