Difference between 9/16”x 20 Cycle Pitch and 9/16”x 20 UNS.

[Michael GilliganParticipant @michaelgilligan61133]

Hopper’s practical approach is of course the appropriate one … if this is a repair job.

If the objective is to produce a functional bicycle, then the practical man uses whatever tools and technique are available … to produce something that works [possibly better than the original].

If, however, this is a restoration job on a ‘significant’ bicycle, then it may be appropriate to identify exactly what the original maker used in the first place.

[ the male threads on the pedals could presumably be measured for starters ]

Perhaps the most academically interesting possibility [as yet unmentioned] is that someone has reason to want a Failure-Mode Analysis … in which case the whole can-of-worms is open!

MichaelG.

[HopperParticipant @hopper]

 

BTW, Bill, 9/16 x 20 BSC taps are on eBay UK for less than 10 Quid a pair, giving both the left and right hand taps in one purchase. Significantly less steep than Tracy’s price for one tap. And probably good enough quality for odd use in the home workshop if you are not going into mass production or specialising in Brough Superiors etc.

Search eBay for “9/16 cycle pedal taps” and plenty of options pop up.

[Michael GilliganParticipant @michaelgilligan61133]

Now that ^^^ is expedient

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

As a general rule, it’s bad practice to mix different thread forms as a convenience.  Maybe acceptable as a bodge, but not when safety matters.   Many accidents caused by mixing threads.

One obvious problem is the class of fit might be compromised.   Either:

• Graunching an over tight connection together damages the threads, or
• The connection is weak and prone to vibrate loose because the threads don’t engage properly.

Bodging when a fastening doesn’t need to be strong won’t do much harm.  But avoid bodging if a fastening coming apart will cost money, cause serious inconvenience, or hurt someone.

Back to Bill’s problem, where it seems a thread is already damaged beyond simply reforming it.   How about welding enough metal into the hole so it can be bored out the the correct size, and then rethreaded?   Easier said than done – I don’t have the gear or the skills.

Dave

[Bill PhinnParticipant @billphinn90025]

Thanks a lot for the further replies.

I’ve spelched in a good quantity of Alusol, after cleaning out the bore and brushing it thoroughly with a stainless wire Dremel wheel.

The Alusol wetted the parent metal very well indeed and a lot less heat was needed than the guy in the video was using. My only reservation is the softness of the solder, which is unlikely to make the repair as durable as the original aluminium. If it fails, I will go the bushing route next time.

A pair of 9/16”x 20 taps have been ordered from Ebay. I just need to think about the final drill size before tapping. I’ve got a 33/64” jobber, but no 13.2mm.

Photos show the soldered bore, and the set-up I plan to use on the mill to ensure drilling and tapping are perpendicular to the crank. Not shown is the toe clamp I intend to put near the end of the crank in line with the “jack” you can just make out underneath.

[JasonBModerator @jasonb]

Probably better to bore the hole as a drill will want to follow the welded hole as well as not being the size ou want

[old martParticipant @oldmart]

That side would have the right hand thread, but I doubt whether the repair would last long with the forces involved.

Many years ago, I bought an aluminium full suspension unified triangle frame from Ballistic. The bottom bracket had been welded on backwards and about ten miles out on my first ride out, the bottom bracket came loose. Fortunately, I had self extracting plugs in the cranks and could remove the pedals and tighten the Shimamo XTR bottom bracket well enough to get me home. It got Loctited in with a weak grade and as it was XTR, it was still going strong when I sold the bike.

[Howard LewisParticipant @howardlewis46836]

So, approximating, the difference in thread form is 0.0013″ truncation and rounding, 0.0026″ on diameter.

Probably needed to allow the internal and external threads to move relative to one another.

A small percentage of the 0.5625″ nominal diameter.

Did one of the angels fall off the pin head?

Howard

[Howard Lewis]

On Howard Lewis Said:

[…]  Did one of the angels fall off the pin head?

Howard

Which part of Bill’s excellently-worded opening request do you not understand, Howard ?

MichaelG.

.

Quote, for convenient reference:

Can anyone tell me what difference, in theory and practice, there is between these two thread types.

 

[Howard LewisParticipant @howardlewis46836]

What Iwas implying, Michael, was that in practical terms, given the clearances necessary to allow relative movement between the two parts, a thou is hardly going to be noticed. Possibly within the tolerances for both parts).

Bear in mind mind that i spent my life trying to solve problems so that production could continue, so approach matters from a different view point from you.  We were driven by fitness for purpose in a high volume production environment

I hope that you can now see that practically the difference in crest/root sizes is unlikely to cause a problem.

Howard

[Howard Lewis]

On Howard Lewis Said:

What Iwas implying, Michael, was that in practical terms, given the clearances necessary to allow relative movement between the two parts, a thou is hardly going to be noticed. Possibly within the tolerances for both parts).

Bear in mind mind that i spent my life trying to solve problems so that production could continue, so approach matters from a different view point from you.  We were driven by fitness for purpose in a high volume production environment

I hope that you can now see that practically the difference in crest/root sizes is unlikely to cause a problem.

Howard

I have been waiting for your reply, Howard … and it is exactly as anticipated !

… I, and I suspect most everyone else that has contributed to this topic, fully appreciate that the differences are very, very, small … but WE have responded to what Bill asked and have discussed the difference in theory and practice between the two thread-forms.

The first part of your Post #760332 was entirely reasonable, but the snide comment about the Angel was inappropriate, irrelevant, and crass.

I am well aware of your lifetime contribution to Engineering … you have mentioned it more than once in these pages … and your patronising attitude is also sadly familiar.

Please just stick to the topic, and resist the temptation to make gratuitous insults that masquerade as clever rhetoric.

We two have, on several occasions, “agreed to differ” and I would suggest that we make that a standing arrangement … Let’s both just have our say and not try to score points !!

Very Sincerely

MichaelG.

 

[egaParticipant @ega]

Also known as precession?

[egaParticipant @ega]

re the OP: I bought some modestly-priced Park Tool brand crank eye taps which worked well enough.

[Howard LewisParticipant @howardlewis46836]

Sadly, Michael, we will continue to disagree.

My references to experience are intended to justify the proposition, not to patronise anyone.

They might even help explain the problem, in some cases.

Rather to highlight the difference between what is vital and what is practically acceptable

I do realise the difference between a malformed chamfer sitting in fresh air, doing nothing and a 5 micro inch CLA, or a 0.00001″ error in a white metal bearing, both of which that can result in every product reducing itself to scrap in a very short running time.

Hence I tend to distinguish between an acceptable difference and one which can lead to disaster.

One of the bad habits that “Fitness for purpose” has bred is little tolerance for hair splitting.

So, yes, we will continue to disagree.

But the debates may help,other readers. We may never know!

Howard

 

[Michael GilliganParticipant @michaelgilligan61133]

For all I know, Howard, you may be Henry Ford reincarnate … and I certainly respect your wealth of experience.

What I wrote, however, was what I felt the need to write.

If we can both keep our posts relevant to the Topic, then I’m sure we can co-exist reasonably comfortably.

I will finish by inviting Edith to sing:

https://youtu.be/Q3Kvu6Kgp88?feature=shared

She does it so much better than I ever could 🙂

 

Peace, or at least a ceasefire, Howard.

MichaelG.

 

 

[Bill PhinnParticipant @billphinn90025]

Thank you for the further contributions.

I ended up plunging down (carefully) with a half inch slot drill and then drilling out to 13mm. Thankfully, there was no drama.

The taps I received are marked “9/16×20 UN” and “HSS”. My only criticism of them is that they are practically plug taps with almost no taper, which could make keeping things straight difficult if you were freehand tapping.

If the present repair fails, I will resort to plan B, which is to use Durafix rods. A dozen or so test solderings with Durafix of large holes drilled in aluminium plate tells me it makes for a pretty strong thread repair.

 

[Howard LewisParticipant @howardlewis46836]

Hopefully, the problem is now in the past, and you now have a durable repair.

Like many repairs, it may even turn out to be better than the original.

Good Luck

Howard

[Michael GilliganParticipant @michaelgilligan61133]

+1

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Micahel,

Happy to cease conflict.

We are addictive Engineers from different backgrounds and hold our views quite strongly, based on our experiences.

The Forum provides lots of interest and information, on matters not directly related our experiences, but fascinating just the same.

Thread drift? Yes Mea culpa in many cases!

Howard

IF only I could type accurately!

[Bill PhinnParticipant @billphinn90025]

Thanks for your feedback, Howard and Michael.

I mentioned in my last post that I’ve been experimenting with Durafix aluminium soldering rods believing it is probably a stronger repair for aluminium than Alusol, which is softer since it contains a lot of lead.

Just a heads up about Durafix: not all rods sold as Durafix are equal. Until today most of my experimenting with Durafix had been with rods bought from Oxford Welding Services. These have been excellent in that the filler metal flows way below the point at which the parent aluminium does and of course it bonds well with the parent metal too.

Today I received, from a different Ebay seller, a package of something described as: “Weld with Ease Using Good Welding Effect Durafix Aluminium Welding Rod”.

These work, in that they bond well to the parent metal and form a strong repair, but their flow temperature is considerably higher than the Durafix from OWS. The temperature needed to reach the flow temperature (I’d estimate 100 degrees C higher) means it’s difficult not to bubble and pit the parent aluminium by the time the job is finished.

Thankfully they were only £6 for ten rods.

[Michael GilliganParticipant @michaelgilligan61133]

A useful update, Bill … Thank You

MichaelG.

[Bill PhinnParticipant @billphinn90025]

No problem, Michael.

An update: I’ve now done (i.e. today) six test pieces, three using Durafix from OWS and three using the mysterious new stuff. I drilled 10.5mm holes in 1” square pieces of 1/4” thick 6082 aluminium, and filled the holes with melted rod. I then drilled to 5mm and tapped M6 in the centre of each filled hole.

To test the strength of the thread I tightened a grade 8 cap screw into the hole using a 125mm long 5mm hex key.

In the case of the OWS Durafix repairs I stopped tightening when the hex key started to bend. The thread and the bond of filler to parent metal were not visibly affected. In the case of the new mystery rods the threaded holes stripped out with ease, long before the hex key started to bend.

So I must revise my earlier statement that the new rods produce a strong repair; evidently they do not, even if they bond well to the parent metal.

I’m not sure what accounts for the weakness and higher melting point in the new rods. The composition of Durafix is suggested in the picture below. Given the differences in behaviour, if any metallurgically savvy people can tell me what the likely difference in composition of the new mystery rods is (more zinc? less zinc? more moldy cheese?) I’d be interested to hear from them.

Perhaps this thread should now have a dual title: the one it’s got already and “The difference between Durafix and Durafix”.

 

[Michael GilliganParticipant @michaelgilligan61133]

I think Durafix [the real one] might be very interested in your findings !

MichaelG.

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