By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

RH vs LH threads

All Topics | Latest Posts

Search for:  in Thread Title in  
John MC14/03/2021 09:02:24
avatar
346 forum posts
40 photos

A few days I had a "zoom" get together with a few cycling friends. One topic of discussion was why do bicycles use left-hand threads in certain places? I let my friends discuss this then jumped in with the right answer.

When I say the "right answer", I mean what I always believed to be the reason. Listening to my friends who are not "engineers" try to work out what is not necessarily an intuitive thing was interesting.

So, over to you guys, whats the reason? I won't give my answer just yet so as not to influence any possible discussion.

David George 114/03/2021 09:16:54
avatar
1601 forum posts
485 photos

Hi John it is obvious that if you used two RH threads on cycle crank ends one of the pedals would keep coming unscrewed. As you pedal and if the correct way installed with LH and RH threads they will tend to tighten as you pedal.

David

AndrewD14/03/2021 09:24:55
8 forum posts
5 photos

In some ways a bicycle is a bit like a bench grinder.

Martin Connelly14/03/2021 09:28:59
avatar
1789 forum posts
190 photos

I don't know if it is the case with all modern cranks but I agree with David on this, when the pedals were the screwed in type they came marked LH and RH on both the pedals and cranks on ones I changed out.

I recently re-did the preload on my mill's spindle bearings and I have a written note on the mill saying LH threads and an arrow to the top nuts. I remember the first time I tackled the job I was puzzled over my inability to get the top locknut loose. There was no visible thread to give a clue so when it finally dawned on me that it was LH I put the note on to make sure I didn't go through the same head scratching in the future. Once again this makes sense from the point of is it tightened in normal use? With the potential for intermittent cuts causing vibration it seems to me that the importance of the nuts tightening in use rather than loosening is quite high.

Martin C

Bo'sun14/03/2021 09:31:08
468 forum posts

Same reason BB threads are left and right handed.

Tim Hammond14/03/2021 09:43:51
64 forum posts

Before the advent of spigot-located roadwheels on large goods vehicles, the securing nuts on the left hand side of these vehicles were always left hand thread, but now with spigots they are all right hand. We were always told that the reason for the LH threads was to stop the tendency for the nuts to unscrew as the wheels rotated, but this no longer seems valid with spigot wheels. Initially with these wheels there was a rash of cases of wheels coming loose and sometimes falling off, but this was overcome by improved materials for wheel studs and nuts and the now extensive use of torque-limiting wrenches to tighten the wheel securing nuts to the correct tension.

ega14/03/2021 09:48:23
2186 forum posts
179 photos
Posted by David George 1 on 14/03/2021 09:16:54:

Hi John it is obvious that if you used two RH threads on cycle crank ends one of the pedals would keep coming unscrewed. As you pedal and if the correct way installed with LH and RH threads they will tend to tighten as you pedal.

David

This explains why a proper pedal spanner is relatively long; you need the leverage to loosen the pedal.

Bo'sun14/03/2021 10:02:11
468 forum posts

Corrosion will also add to the force required to remove pedals. Pedals are a sort of "fit & forget" component.

SillyOldDuffer14/03/2021 10:09:27
Moderator
7341 forum posts
1617 photos

Well I've read 'Zen and the Art of Motorcycle Maintenance', which asserts there are two ways people view technology. The romantic view is all about appearances, imagination and creativity, and feelings matter far more than facts. The classical view focuses on reason, facts and design. Thus there's a collision between riding a motorbike, which is romantic, and maintaining it which is classical, made worse because many people can only think in one mode. Engineers who don't care about looks as long as it works, who delight in slag heaps, and Lay persons who can't cope with a screwdriver, but have earned enough money to fill their homes with expensive art work. 'Nude, Green Leaves and Bust' sold for $100M and there's no point in only owning one Picasso!

Unimaginative Classical and Romantic thinkers may be so extreme in their views as to despise each other, which is bad news to any endeavour relying on teamwork to make a profit!

Given the dichotomy between Classical and Romantic thinking, the engineer uses left-handed threads for engineering reasons but romantic users believe it's done to confuse and humiliate them - yet another reminder they don't understand how the physical world works, which contradicts their view that they are the masters and technology the servant.

Meanwhile, the chap who understands left-handed threads believes he should be running the world, despite copious evidence engineers don't understand the 'what we want' people issues driving politics, religion, economics, myths, pseudo-science, and fashion...

Schulz captured the collision when Snoopy decided he was the Red Baron:

Imagining himself to a heroic WW1 aviator with a life full of high-adventure, the truth is he's just a dog, sat oh his kennel, wearing a scarf and flying helmet. That's you and I...

devil

Dave

PS. Reading the book, which is about values and the 'Metaphysics of Quality', I found the first half delightfully readable but the second half blew my mental fusebox. It plunges deep into the meaning of 'quality' and is too hard for me: I'd be grateful If anyone can explain part two in simple terms!

The book is one of the reasons I dislike 'quality' so much; either the word is meaningless without a specification, or the concepts are beyond my comprehension.

 

 

 

Edited By SillyOldDuffer on 14/03/2021 10:10:04

Hopper14/03/2021 10:19:00
avatar
5505 forum posts
137 photos

The only way to explain that book is the book itself. Good luck. You are trying to understand it in the classical way, like the first half. Try the Romantic way. Its all about how the book makes you feel.

laugh

Even Pirsig struggled to define Quality as he meant it. Something to do with subject and object becoming one. Maybe. EG when you become "totally involved" in machining a piece and forget about the surrounding world. Your hands are operatiing the lathe control handles, your mind is absorbed in the cutting of the metal by the tool. So you are probably doing Quality every day, just didnt know it.

 

 

Edited By Hopper on 14/03/2021 10:35:57

Hopper14/03/2021 10:21:54
avatar
5505 forum posts
137 photos

ISTR too that the bearing retaining ring-nut on the lefthand side of the old bicycles' bottom bracket (pedal axle bearing housing) was also left hand thread so it tightened as one pedalled.

Bazyle14/03/2021 10:30:33
avatar
5920 forum posts
220 photos

re that bearing retaining nut - why are the spanner flats on them rounded off so they are impossible to grip?

Hopper14/03/2021 10:37:41
avatar
5505 forum posts
137 photos
Posted by Bazyle on 14/03/2021 10:30:33:

re that bearing retaining nut - why are the spanner flats on them rounded off so they are impossible to grip?

So you have to buy the special spanner with the big hole in it that is rounded at the ends and flat in the middle. (Or use a hammer and chisel as our old man taught us on the "new" bikes we bought home from the tip.)

Howard Lewis14/03/2021 10:40:22
5036 forum posts
13 photos

Left Hand threads are relatively more difficult to make, so are only used where really needed, but do have their uses.

Left Hand threads are also used in conjunction with right hand threads in such places as scissor jacks for cars, and turnbuckles to adjust the length of straining wires or links..

In other places, (Such as pulleys in vacuum cleaners, or one end of a bench grinder, as on bicycles ) they are used to prevent the item unscrewing during normal use.

The nut that retains the pulley on top of the quill on my Mill/Drill uses a Left Hand Thread.

Howard

Nicholas Wheeler 114/03/2021 10:55:27
642 forum posts
46 photos
Posted by SillyOldDuffer on 14/03/2021 10:09:27:PS. Reading the book, which is about values and the 'Metaphysics of Quality', I found the first half delightfully readable but the second half blew my mental fusebox. It plunges deep into the meaning of 'quality' and is too hard for me: I'd be grateful If anyone can explain part two in simple terms!

It's utter drivel.

Is that simple enough?

Dave Halford14/03/2021 10:57:33
1590 forum posts
16 photos
Posted by Tim Hammond on 14/03/2021 09:43:51:

Before the advent of spigot-located roadwheels on large goods vehicles, the securing nuts on the left hand side of these vehicles were always left hand thread, but now with spigots they are all right hand. We were always told that the reason for the LH threads was to stop the tendency for the nuts to unscrew as the wheels rotated, but this no longer seems valid with spigot wheels. Initially with these wheels there was a rash of cases of wheels coming loose and sometimes falling off, but this was overcome by improved materials for wheel studs and nuts and the now extensive use of torque-limiting wrenches to tighten the wheel securing nuts to the correct tension.

And the little yellow plastic pointer tell tales.

ega14/03/2021 11:04:58
2186 forum posts
179 photos
Posted by Bo'sun on 14/03/2021 10:02:11:

Corrosion will also add to the force required to remove pedals. Pedals are a sort of "fit & forget" component.

Hence the rule of thumb to "grease all threads".

Nicholas Farr14/03/2021 11:16:37
avatar
2864 forum posts
1295 photos

Hi, or better still, use anti-seizing compound, as grease can dry out over time and go quite hard.

Regards Nick.

Tony Pratt 114/03/2021 11:27:34
1583 forum posts
8 photos
Posted by Howard Lewis on 14/03/2021 10:40:22:

Left Hand threads are relatively more difficult to make, so are only used where really needed, but do have their uses.

That statement made me chuckle, so thanks for that!smiley

Tony

Hopper14/03/2021 11:28:33
avatar
5505 forum posts
137 photos
Posted by Nicholas Wheeler 1 on 14/03/2021 10:55:27:
Posted by SillyOldDuffer on 14/03/2021 10:09:27:PS. Reading the book, which is about values and the 'Metaphysics of Quality', I found the first half delightfully readable but the second half blew my mental fusebox. It plunges deep into the meaning of 'quality' and is too hard for me: I'd be grateful If anyone can explain part two in simple terms!

It's utter drivel.

Is that simple enough?

Either that or you don't understand it. Bit like the Romantic with the left hand thread that SOD mentioned. laugh

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
cowells
Eccentric July 5 2018
emcomachinetools
JD Metals
Warco
ChesterUK
walker midge
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest