Rabbie
Well-Known Member
Having removed the nut, the propellor slid off no problem. What surprised me was no key-way or anything to secure prop to shaft, except 'grip' on the tapered shaft. Is this common, as I expected to find a key?'
Prop shaft.
- Thread starter Rabbie
- Start date
david_bagshaw
Well-Known Member
common though usually the prop s tghtly on
used on sh ps as less stress wthout ey.
sorry about m ss ng letters
used on sh ps as less stress wthout ey.
sorry about m ss ng letters
capsco
Well-Known Member
No it is most unusual, are you sure the prop has not turned on the shaft and "machined" the key flush?
Rabbie
Well-Known Member
No, there is no indication of wear or anything!. I have had no adverse effects on speed and no apparent signs of 'slipping'. Wierd eh?. Maybe its as David suggests?.
supermalc
Well-Known Member
I would agree this is unusual. All my props I bought last year had keyways, and when discussing this with my friend, while making my new propshaft last winter, we realised it is important as the shaft turns the prop BOTH ways.
I had to cut my keyway with an angle grinder, in the absence of a milling machine. I thankfully managed to do a good job, and the key I made was a tight fit, in both the prop and shaft.
Have you a keyway in the prop. Even if it has sheared there should be some left unused. Clean both prop and shaft with fine emery, just to be sure.
I had to cut my keyway with an angle grinder, in the absence of a milling machine. I thankfully managed to do a good job, and the key I made was a tight fit, in both the prop and shaft.
Have you a keyway in the prop. Even if it has sheared there should be some left unused. Clean both prop and shaft with fine emery, just to be sure.
Rabbie
Well-Known Member
Thanks for ideas. I will have a closer look at the weekend when I next visit her.
Stemar
Well-Known Member
My snapdragon has a keyway, and IIRC, all the shafts I saw at the Bursledon Barge had them. Does the prop have a keyway?
It should be obvious if a key in the shaft has been eaten somehow. The shaft's stainless and I think the key's bronze, so they'll be different colours. If the whole taper is bronze coloured, that would suggest the prop has been slipping and further investigation would be in order as Malcolm suggests.
It should be obvious if a key in the shaft has been eaten somehow. The shaft's stainless and I think the key's bronze, so they'll be different colours. If the whole taper is bronze coloured, that would suggest the prop has been slipping and further investigation would be in order as Malcolm suggests.
tyce
Well-Known Member
there should definetly be a key, i wonder if the boat has had a new shaft made at some point in its life, and the keyway was ommitted.
the fact that you said the propeller slipped off no problem proves it needs a keyway, it would be fine going forward as the prop will wind its way up the shaft, but in reverse its a different matter.
i chattered a jenneau in the med and the shaft came loose at the coupling due to no key when reversing out of port, it certainly helped get the lead crews attention.
just to follow up on what david said about ships, its a different thing all together as the method they use is the hub is actually forced to expand and then pushed up the shaft using massive hydraulic pressure, when the pressure is released the hub shrinks and is tight on the shaft.
the fact that you said the propeller slipped off no problem proves it needs a keyway, it would be fine going forward as the prop will wind its way up the shaft, but in reverse its a different matter.
i chattered a jenneau in the med and the shaft came loose at the coupling due to no key when reversing out of port, it certainly helped get the lead crews attention.
just to follow up on what david said about ships, its a different thing all together as the method they use is the hub is actually forced to expand and then pushed up the shaft using massive hydraulic pressure, when the pressure is released the hub shrinks and is tight on the shaft.
jerryat
Well-Known Member
That's a real surprise. I've never even seen a prop/shaft without a keyway!! I note others have, but I simply cannot see how this causes stress, is good engineering, or sensible. /forums/images/graemlins/confused.gif
Lord knows how tight one is expected to tighten the prop nut before 'friction' stops the thing moving round the shaft. Praps it's some kind of new anti-tangle idea for when you pick up a rope. Doesn't cut it or wreck the shaft et al, just turns! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
Lord knows how tight one is expected to tighten the prop nut before 'friction' stops the thing moving round the shaft. Praps it's some kind of new anti-tangle idea for when you pick up a rope. Doesn't cut it or wreck the shaft et al, just turns! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
boatmike
Well-Known Member
With due respect I have worked in the shipbuilding and boatbuilding industries all my life and never seen a prop fitted on a taper without a key. I have however seen keys shear and the rotating prop machine the shaft so that it appears there is none. Look in the prop keyway for the broken end of the key. If you find it inspect the shaft carefully. If its a woodruff key (likely) you will probably be able to remove it by punching one end down.
seaesta
Well-Known Member
The grip of a taper is amazingly strong. I suspect that prop shaft keys are redundant on well engineered shafts and props and they are there by convention in a notoriously conservative market. I expect when they actually function to prevent the shaft turning relative to the prop then they simply chatter or shear away. So if you have no problem with your shaft and prop why change it? Thats my ten pennyworth.
Meantime I must admit to using the key that is fitted to my own prop shaft.
Martin
Meantime I must admit to using the key that is fitted to my own prop shaft.
Martin
john_morris_uk
Well-Known Member
I am not contradicting you Mike - except to say that I HAVE seen a shaft and prop without a keyway. Our old SCOD had a Dolphin engine which was u/s when we bought it and the prop had no keyway. Long story about how I also lost the prop at Cowes week trying to be clever - but another day...
eyehavit
Well-Known Member
It is rare, but we have worked with OEM vessels from 2" to 5" diameter shafts that ran keyless shaft/prop combos. The system relies completely on a precise interference fit. Using hydraulic pressure, the prop is pressed over the shaft to a pre-determined mark.
tcm
...
Re: taper interference fit
yes, i've seen this as well. But as eyehavit says, it relies on a tight interference fit.
Imho, it's good because there are no stress points caused by the key or keyway. The tolerances have to be tight, else it won't work.
The gear/prop might be forced on hydrualically, or simply using retaining nut on the outside of the taper forcing the gear/prop up to a mark or (bettter) up to a shoulder on the shaft.
You were lucky that it just slid off no problem - cos it can be almost without the right gear, as follows.
Usually, if gears/props are fitted this way I have also seen a means to hydraulically release the gear/prop using hydrulic pressure: theres is a small hole (just a couple of mm is fine) drilled in diametrically from the surface of the gear/prop inwards through to the internal bore. The shaft is not touched. At the outer surface, the hole is tapped to fit a small pipe fitting.
Then to release, the nut is released a small amount (but not taken off) and a hydraulic handpump or similar can be used to force oil down the hole to quite high pressure. With a few pumps the gear/prop releases, often quite suddenly hence leave the nut on the shaft to avoid the prop crashing to the floor.
Is there such a hole in evidence on the prop? Or is it possible that you could get an do this? When refitting, off course, the spline and internals should be clean and dry. If such a hole cannot be found, I'd get an engineering shop to set this up before refitting and ask for a blanking plug on the release hole to avoid damage/barnacles to the oilway whilst in use.
yes, i've seen this as well. But as eyehavit says, it relies on a tight interference fit.
Imho, it's good because there are no stress points caused by the key or keyway. The tolerances have to be tight, else it won't work.
The gear/prop might be forced on hydrualically, or simply using retaining nut on the outside of the taper forcing the gear/prop up to a mark or (bettter) up to a shoulder on the shaft.
You were lucky that it just slid off no problem - cos it can be almost without the right gear, as follows.
Usually, if gears/props are fitted this way I have also seen a means to hydraulically release the gear/prop using hydrulic pressure: theres is a small hole (just a couple of mm is fine) drilled in diametrically from the surface of the gear/prop inwards through to the internal bore. The shaft is not touched. At the outer surface, the hole is tapped to fit a small pipe fitting.
Then to release, the nut is released a small amount (but not taken off) and a hydraulic handpump or similar can be used to force oil down the hole to quite high pressure. With a few pumps the gear/prop releases, often quite suddenly hence leave the nut on the shaft to avoid the prop crashing to the floor.
Is there such a hole in evidence on the prop? Or is it possible that you could get an do this? When refitting, off course, the spline and internals should be clean and dry. If such a hole cannot be found, I'd get an engineering shop to set this up before refitting and ask for a blanking plug on the release hole to avoid damage/barnacles to the oilway whilst in use.
TheBoatman
Well-Known Member
Re: taper interference fit
You maybe surprised to know that all large ships props are held on keyless tapered shafts. They rely solely on the interference fit. (20.000HP - no probs)
Admittedly smaller shafts tend to come with a key but this adds little to the "drive". Providing that the tapers are matched then the drive comes from the fit and not the key, after all think about it, if you drove exclusively on the key then why bother with a tapered shaft?
Driving the prop onto the shaft to a set distance is more to do with the stresses placed on the shaft and prop hub than the amount of drive you will get. Once the tapers "lock" then any amount of winding on the nut will not necessarily improve the drive only distort the hub.
As an example, if you go into an engineering shop and look at any large drilling machine you WON'T find parallel drills much above 1/2" all the rest are run on MORSE TAPERS (no keys) I have drilled holes up to 2" dia through some seriously thick plate just relying on the taper drive!!!
You maybe surprised to know that all large ships props are held on keyless tapered shafts. They rely solely on the interference fit. (20.000HP - no probs)
Admittedly smaller shafts tend to come with a key but this adds little to the "drive". Providing that the tapers are matched then the drive comes from the fit and not the key, after all think about it, if you drove exclusively on the key then why bother with a tapered shaft?
Driving the prop onto the shaft to a set distance is more to do with the stresses placed on the shaft and prop hub than the amount of drive you will get. Once the tapers "lock" then any amount of winding on the nut will not necessarily improve the drive only distort the hub.
As an example, if you go into an engineering shop and look at any large drilling machine you WON'T find parallel drills much above 1/2" all the rest are run on MORSE TAPERS (no keys) I have drilled holes up to 2" dia through some seriously thick plate just relying on the taper drive!!!
Stemar
Well-Known Member
Re: taper interference fit
I don't know about other peoples set ups, but my prop nut has one hole drilled through it and this has to match with one hole in the shaft, so I can only tighten or loosen by 1/2 a turn - the best part of a millimetre. If I want to put the pin in, the nut's too loose - it isn't even finger tight, because I can't do it up another half turn.
Do I need to shim it? If so, where do I get shims?
Any other suggestions?
I don't know about other peoples set ups, but my prop nut has one hole drilled through it and this has to match with one hole in the shaft, so I can only tighten or loosen by 1/2 a turn - the best part of a millimetre. If I want to put the pin in, the nut's too loose - it isn't even finger tight, because I can't do it up another half turn.
Do I need to shim it? If so, where do I get shims?
Any other suggestions?
tugboat
Well-Known Member
Re: taper interference fit
Just put a washer between the prop and the nut, using trial and error to get the right thickness. Better still, use a castellated nut.
Just put a washer between the prop and the nut, using trial and error to get the right thickness. Better still, use a castellated nut.
seaesta
Well-Known Member
Re: taper interference fit
I had this problem and so I simply tightened the nut and then drilled a new hole through the nut and shaft then put a pin through both.
If you do this and have stainless gear you will neeed to drill very slow and with a significant cut to prevent work hardening.
Martin
I had this problem and so I simply tightened the nut and then drilled a new hole through the nut and shaft then put a pin through both.
If you do this and have stainless gear you will neeed to drill very slow and with a significant cut to prevent work hardening.
Martin
savageseadog
Well-Known Member
Re: taper interference fit
I solved this problem by lapping the nut down using wet and dry sandpaper on a flat surface. Just take enough off.
I solved this problem by lapping the nut down using wet and dry sandpaper on a flat surface. Just take enough off.
duncanmack
Well-Known Member
The fact that it slipped off easily proves that it was not properly on the taper. It should have needed a sharp bang (or two) with a hammer to get it off the taper.
Tapers are good engineering practice. Remember the mini? The engine flywheel was held on a taper. Required severe treatment to jar it off - and if you did it wrong you smashed the flywheel. Citroen 2CV - crankshaft pulley (to drive alternator) with air-cooling fan mounted on a taper and could be a right B to get off.
Track rod ends on virtually all vehicles - tapers. Lots of suspension ball joints - tapers.
It's the friction on the taper which makes it work. Exactly the same sound engineering principle which bolts use. It's NOT the bolt that holds things together, it's the friction caused between the bits by the tension applied by the bolt. High tension bolts can be tightened more and thus can apply more friction between the bits being held.
A key is only required if there is a need to keep a shaft and pulley indexed. eg. timing an engine. Old british motorbikes commonly had tapered shafts and no keyway/keys. They were a proper sod to set up the timing on. However, once set up and tightened they didn't move unitl you had to remove them.
Tapers are good engineering practice. Remember the mini? The engine flywheel was held on a taper. Required severe treatment to jar it off - and if you did it wrong you smashed the flywheel. Citroen 2CV - crankshaft pulley (to drive alternator) with air-cooling fan mounted on a taper and could be a right B to get off.
Track rod ends on virtually all vehicles - tapers. Lots of suspension ball joints - tapers.
It's the friction on the taper which makes it work. Exactly the same sound engineering principle which bolts use. It's NOT the bolt that holds things together, it's the friction caused between the bits by the tension applied by the bolt. High tension bolts can be tightened more and thus can apply more friction between the bits being held.
A key is only required if there is a need to keep a shaft and pulley indexed. eg. timing an engine. Old british motorbikes commonly had tapered shafts and no keyway/keys. They were a proper sod to set up the timing on. However, once set up and tightened they didn't move unitl you had to remove them.
