Flexofold fitting - sanity check

[Overandunder]

Evening all. I have recently bought a 2 blade Flexofold (to replace the stock fixed blader) on my 2006 SO 29.2.

Simple enough, I hear you cry. With instructions to hand I made a trial fit - and from this a question arises. The instructions state that the key may well need filing down to suit.

The first pic shows the hub unit slid into place with no key (forgive the state of the cutlass - it's days are numbered). It's a good fit and as far as I can tell the taper is correct. Note the black line marked on the shaft as per instructions.

The 2nd shows the hub refitted - this time with the key slotted into the keyway. You can see that the difference is significant - to get the hub back to the marked line is going to take an awful lot of filing of the key.

So - before I break the files out, could someone estimate that I'm on the right track here- or should I just look for a thinner key ?

Thanks all

 

[wonkywinch]

"Remove the wedge (3) from the shaft (2). Slide the hub onto the shaft (2) and check to make sure it fits correctly and the hub does not rock. The fit must be in order without gaps between the parts. Mark on the shaft (2) where the bottom of the hub reaches. Remove the hub again, put the wedge (3) back into the cone of the shaft (2). Degrease the cone of the shaft and the cone in the hub thoroughly. Slide the hub (1) gently over the cone of the shaft (2). Make sure the wedge stays in place and does not pinch the hub. There must be air between the top of the wedge and the bottom of the wedge track/keyway in the hub. When mounted, the hub should reach the mark you placed on the shaft. If the hub does not reach the mark on the shaft, remove the hub. The height or width of the wedge can be reduced with an ordinary hand file, until the hub reaches the mark on the shaft"



They call the (woodruff) key a wedge.

From the installation manual..

Installing and mounting your Flexofold folding propeller

Installation - 2-Blade Shaft Folding Propeller

 

[NormanS]

Just to be clear about terminology, the key sits in the keyway. It'll be the key that may need to be filed down a bit. First, make absolutely sure that the prop fits the taper. Traditionally this would be done using "engineer's blue", lightly smeared on the shaft, and by rotating the propeller, to show how much is in contact. It's the actual taper contact which gives the drive. The key is there as a backup, and there must be clearance between the top surface of the key and the keyway in the prop. It's a simple job with a file to reduce the height of the key, enough to allow the propeller to go as far as it went when the key wasn't in place.

 

[Overandunder]

"Remove the wedge (3) from the shaft (2). Slide the hub onto the shaft (2) and check to make sure it fits correctly and the hub does not rock. The fit must be in order without gaps between the parts. Mark on the shaft (2) where the bottom of the hub reaches. Remove the hub again, put the wedge (3) back into the cone of the shaft (2). Degrease the cone of the shaft and the cone in the hub thoroughly. Slide the hub (1) gently over the cone of the shaft (2). Make sure the wedge stays in place and does not pinch the hub. There must be air between the top of the wedge and the bottom of the wedge track/keyway in the hub. When mounted, the hub should reach the mark you placed on the shaft. If the hub does not reach the mark on the shaft, remove the hub. The height or width of the wedge can be reduced with an ordinary hand file, until the hub reaches the mark on the shaft"

View attachment 186280

They call the (woodruff) key a wedge.

From the installation manual..

Installing and mounting your Flexofold folding propeller

Installation - 2-Blade Shaft Folding Propeller

Thanks - I already have those.

 

[wonkywinch]

How deep is the keyway in your old prop vs the Flexofold? If there is a big difference, time to start filing!

 

[Overandunder]

Just to be clear about terminology, the key sits in the keyway. It'll be the key that may need to be filed down a bit. First, make absolutely sure that the prop fits the taper. Traditionally this would be done using "engineer's blue", lightly smeared on the shaft, and by rotating the propeller, to show how much is in contact. It's the actual taper contact which gives the drive. The key is there as a backup, and there must be clearance between the top surface of the key and the keyway in the prop. It's a simple job with a file to reduce the height of the key, enough to allow the propeller to go as far as it went when the key wasn't in place.

Exactly - amended my post but I think most got the jist. It's not that I don't understand what's required - it just seems a huge amount to take off the key ??

 

[wonkywinch]

Exactly - amended my post but I think most got the jist. It's not that I don't understand what's required - it just seems a huge amount to take off the key ??

Presumably the shaft maker supplied the key, not Flexofold, hence my question to check slot depth inside both props before the correcting tool is used.

 

[Overandunder]

How deep is the keyway in your old prop vs the Flexofold? If there is a big difference, time to start filing!

That I will need to compare - out with the micrometer next I think.

 

[Overandunder]

Presumably the shaft maker supplied the key, not Flexofold, hence my question to check slot depth inside both props before the correcting tool is used.

Exactly. I don't think Flexofold supply keys afaik (I learnt tonight they are known as a 'feather key').

I will compare the old and new as you suggest. Interesting that it's the taper and not the key that provides the friction - hub to shaft.

 

[wonkywinch]

I get the collywobbles every time I see a woodruff key.

My first motor propelled vehicle was an NSU Quickly. With annoying regularity, it snapped the key on the magneto shaft when I closed the throttle because the taper match was poor. I used to carry a pocket full of them.

I tried valve grinding paste etc but nothing ever worked. As soon as I was 17 and passed my test, I bought a Mk1 Cortina.

 

[DinghyMan]

As NormanS mentions above the prop should be matched to the taper, and vice versa, Keith Fenner has a few good videos on Youtube showing the proper process e.g.

 

[earlybird]

Perhaps not that much filing required. If, say, an imperial shaft at 1:12 taper, filing just 1/32" off the key will give 3/8" extra engagement of the taper, which looks roughly what you might need guesstimating from the photos.. A metric shaft is likely to be 1:10. What you must ensure of course is that the prop retaining nut fully engages with the shaft thread without bottoming on the small end of the taper with the taper tightly engaged.