Morning quiz! Name that thread...

MagicalArmchair

MagicalArmchair

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So Flexofold have sent me the correct hub for my prop, however they have sent me a hub nut that has the wrong thread. I sent them my old nut which they identified as 3/4"-10 UNC - clearly it is not (It only does up a couple of threads and then locks)... although from the below is does look like 10 TPI. Its a 1 inch shaft.

qjXIuahl.jpg


I didn't have any of my thread gauges with me (I was going down to fit the prop - not measure the thread of the shaft!) - what's your best guess?
 
3/4" Whitworth is 10tpi but a different thread form from UNC (so close they are often considered interchangeable but it may depend on tolerances).
3/4" BSF is 12tpi.
 
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Thanks all. Interesting, it is definitely a 1" shaft and not a 25mm one (a mistake I have made previously (I ordered the wrong hub from Flexofold to start with :hopeless:, hence I sent them my old prop plus nut as reference to make sure there were no more)).

3qtLjsBm.jpg


Plevier, perhaps it is 3/4" BSF? And Len Ingalls, in the notes on that page "Threads on older supply could differ. Imperial threads were usually B.S.F. or B.S.W." it backs up what Plevier said. Could it be 12TPI as opposed to 10TPI...?

qjXIuahl.jpg
 
Okay, so that's confirmed, it is NOT a 3/4" BSF thread. It feels 'tight' in the same way the nut from Flexofold felt tight (only does up a few threads) - so I've ordered a cheap 3/4" Whitworth nut to test the theory the shaft might be this thread: Have I missed any other 3/4 threads it could potentially be of circa 10 TPI?
 
MagicalArmchair said:
Okay, so that's confirmed, it is NOT a 3/4" BSF thread. It feels 'tight' in the same way the nut from Flexofold felt tight (only does up a few threads) - so I've ordered a cheap 3/4" Whitworth nut to test the theory the shaft might be this thread: Have I missed any other 3/4 threads it could potentially be of circa 10 TPI?
Click to expand...

You need to borrow thread pitch gauge(s) to accurately determine what it is.
Over here it would be 3/4" UNC 10 TPI. Over there-who knows? Too many options over the years.
Also,threads could be distorted slightly & need a thread runner or die passed over them.
Good luck / Len :)
 
Thanks Len, I do actually have thread gauges buried in my garage that I need to dig out (note to self, should have got these out first...), so when I take the BSW threaded nut down to the boat - just in case that one doesn't fit, at least I'll have a backup plan this time... :rolleyes:! The thread looks in pretty good nick on the shaft - the bright few threads on the end are where the Flexofold nut was tight when I offered it up (clearly I didn't apply any force to it for fear of knackering the thread), so I would be mightily surprised if it were this.

Needless to say the nut that came off and was subsequently sent to Flexofold went up and down the thread err, if you can forgive the pun, sweet as a nut.
 
MagicalArmchair said:
Okay, so that's confirmed, it is NOT a 3/4" BSF thread.
Have I missed any other 3/4 threads it could potentially be of circa 10 TPI?
Click to expand...

The reason I asked my question in #8 was because I once had a 13/16" nut on a shaft (manufactured in 1995 - there was a specific warning about it in the associated paperwork as everything else was metric). I deal preferably in electrons and therefore plead ignorance, but I am told that 13/16"BSW was 10tpi.

RIBW
 
RIBW said:
The reason I asked my question in #8 was because I once had a 13/16" nut on a shaft (manufactured in 1995 - there was a specific warning about it in the associated paperwork as everything else was metric). I deal preferably in electrons and therefore plead ignorance, but I am told that 13/16"BSW was 10tpi.

RIBW
Click to expand...

Correct but not common. I don't think you would get a 3/4" nut started on a 13/16" shaft though unless seriously under spec. But what is the thread OD with your vernier - I assumed you had confirmed it is .75?
 
Thanks chaps, I'll take my vernier down as well next time as out of the many measurements of the taper and shaft I took, that wasn't one of them! I checked three times as I was sure I had taken one. Tomorrow I am wizzing down to the marina on my lunch break with all measuring devices I can lay my hands on, so hopefully the I'll have a better idea (so long as I can find those pitch gauges...)

This is a cautionary tale - I should have gone to Darglow (Flexofolds UK agent) and not directly to Flexofold. It 'saved' me £200 or thereabouts, however it has been easily that in aggravation. In all fairness to Flexofold, they have been very helpful - they have just not successfully reached a solution (yet).

Their last response was:

"Honestly speaking, I´m very surprised about your recent emails.
We did use very accurate measure (thread gauges) to make sure that the old and new nut had the same thread.
So I really don´t know what to say.
Hope that the one you get yourself will fit(!) Wondering if the problem is due to a damage on the shaft thread?"

The fact was the nut I sent them went up and down the thread beautifully - thus I can only conclude it was a measuring error at Flexofolds end, which is unsurprising. Its harder to read a thread gauge on a nut compared to a stud...
 
Plevier wins the quiz! 3/4 Whitworth it is... now to get a prop nut from Denmark and I can actually attach my new shiny prop (at long last)... :cool-new:

One thing that surprised me is the torque Flexofold recommended to do the nut up to - they suggested only 25Nm... now to my mind that sounds exceedingly light on a 3/4 nut holding my new favourite toy in place...

Don't tell, just get it tight and don't worry about it :) I work on cars too so am I bit of a slave to my torque wrench and the last thing I want to do is lose my prop!
 
MagicalArmchair said:
.One thing that surprised me is the torque Flexofold recommended to do the nut up to - they suggested only 25Nm... now to my mind that sounds exceedingly light on a 3/4 nut holding my new favourite toy in place.
..QUOTE]
The pdf I downloaded for fitting my 2-blade Flexofold says tighten the shaft nut "very tight".
(A normal recommendation for 3/4" whit. would be way more than 25Nm I'd have thought ).
The small locking screw torques are shown as 10-12 Nm.
Incidentally, I ordered from Denmark, despite specifying M16, the nut came as a blank, which I had to thread.
Overall, I didn't save much on the price either.
Click to expand...
 
MagicalArmchair said:
Plevier wins the quiz! 3/4 Whitworth it is... now to get a prop nut from Denmark and I can actually attach my new shiny prop (at long last)... :cool-new:

One thing that surprised me is the torque Flexofold recommended to do the nut up to - they suggested only 25Nm... now to my mind that sounds exceedingly light on a 3/4 nut holding my new favourite toy in place...

Don't tell, just get it tight and don't worry about it :) I work on cars too so am I bit of a slave to my torque wrench and the last thing I want to do is lose my prop!
Click to expand...

Jolly good! I'm quite surprised if a correctly made UNC nut wouldn't go on, you must be on the extremes of tolerances.
You could try putting a Whit tap through the UNC nut - with a delicate touch - or run a UNC die down the shaft thread. Better to get a new nut really though if you have time.
Is the prop on a taper? If so and you do it up to normal 3/4" torque (270-400Nm depending on grade) you'll never get it off again. Must agree 25Nm isn't a lot. Is it locked with a pin or something?
 
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