Left vs right thread 1

[Loco_]

Hello all,
My first thread on this forum.
Could someone explain to me when the left-hand thread is used? Till yesterday, I thought that when a shaft or pulley is rotating clockwise, the right thread is used because it is the direction of tightening, and this will prevent the bolt from coming loose. I saw this on some designs like bicycle pedals; on the left one, the thread is left, and on the right pedal, the thread is right-hand. But when I was rebuilding a car turbocharger, I noticed that a compressor turns clockwise and has a left thread nut. It's the opposite of what I was thinking. I am confused now, and for some of my designs, I need to be 100 % sure when to use the left thread.
Thanks in advance. Matthew.

 

[TugboatEng]

If the compressor turns clockwise, the reaction is counterclockwise, hence the left hand thread causes the compressor to tighten itself onto the shaft.

Left hand thread can be beneficial for connections that rotate in one direction around a single bolt or nut.

 

[Denial]

I can only talk for bicycle threads. These differ between sides so that if there is any friction between the rotating part of the pedal and the fixed part (the part you screw into the crank arm), then on BOTH sides that friction will tend to drive the pedal further INTO the shank rather than out from it. The latter result could be a bit unpleasant.

 

[EdStainless]

If you can design the junction so that the bears at an angle (mating chamfers) then there is no reason to use left hand threads.
This why auto lugs don't have to have left hand threads.
Bike pedals wouldn't either if they had a tapered seat for the joint.
Picture the joint involved, if you grabbed the part while it was running would it loosen or tighten?

 

[mfgenggear]

It's common for left hand threads getting damaged. Because trying to remove it.
The wrong g direction.

 

[3DDave]

Not all auto lugs use right hand only. There are a few cars that also used left hand. Chrysler, if Quora is to be believed, used left hand up until 1975.

Bike pedals, unlike lugnuts, see an oscillating bending direction to the loading, tending to overcome the initial pre-load on one half the thread which can allow the pedal to walk out. Pedals also don't give a lot of access to apply significant torque to the joint and, with the large section to take the bending load and short engagement, don't offer much elongation to maintain a preload that would be required to ensure that the oscillating bending load would never overcome the pre-load.

 

[Loco_]

Thanks, all for replying. It helps me.

 

[mfgenggear]

Not all auto lugs use right hand only. There are a few cars that also used left hand. Chrysler, if Quora is to be believed, used left hand up until 1975.

Bike pedals, unlike lugnuts, see an oscillating bending direction to the loading, tending to overcome the initial pre-load on one half the thread which can allow the pedal to walk out. Pedals also don't give a lot of access to apply significant torque to the joint and, with the large section to take the bending load and short engagement, don't offer much elongation to maintain a preload that would be required to ensure that the oscillating bending load would never overcome the pre-load.

Yes my 1983 ford f250 , if I remember left rear had Left hand threads. Bamboozled the tire shop
They could not get the lug nuts off .
Until I instructed them it was left hand thread.
I hed aluminum alloy custom rims .
The lug nuts would not work on a steel rim.
So I had to have one set lh and an other rh
Standard lug nut in the truck tool box what pita.

 

[TugboatEng]

Ford used the left hand thread on one side of their trucks and vans for quite some time. I think this is a good example of an engineer making a bad decision, getting it elevated to production, and the inertia of such a large organization making the bad decision impossible to fix.

 

[mfgenggear]

I imagine there areas where left hand threads are clearly marked in manuals , all types of hardware.
Like power tools, like a grinding wheel turns clockwise. And a nut to hold it was left hand thread. I purchase ryobi cordless hand saw. To replace the blade it had Left hand thread.

 

[Flying Whale]

If I recall correctly, silencers are fitted on weaponry using a left-handed thread, I believe it's because barrels are most commonly rifled in a right-handed direction, and the blast would undo a right-handed silencer.

 

[3DDave]

There may be a condition on the turbocharger that produces a large angular acceleration so that right hand threads on the fastener would tend to release.

Recall that torque is applied by the exhaust side of the turbocharger from the turbine to the compressor shaft and is trying to accelerate anywhere from some coasting RPM to an operating RPM of 80,000 RPM to 250,000 RPM in a few seconds. If the compressor is turning clockwise in normal operation, then that acceleration will drive a the inertia of a right hand thread backwards and tend to unscrew it. When slowing down, the air on the turbine side will become rarefied and there will be considerable lower acceleration when slowing.

While not explained in detail the need is covered here: https://www.melett.com/technical/why-turbos-fail/loose-shaft-nut/

In the vast majority of turbochargers, the shaft nut thread direction is opposite to the direction of rotation on the shaft. If the compressor wheel rotates clockwise, the shaft nut threads should be left-handed – if this is not the case the nut has the potential to become loose during operation.

 

[dgeesaman]

If I recall correctly, silencers are fitted on weaponry using a left-handed thread, I believe it's because barrels are most commonly rifled in a right-handed direction, and the blast would undo a right-handed silencer.

Suppressor and muzzle brake threads are right hand.

But yeah use left hand threads in basically any application where right hand threads would loosen.

One other special case is tie-rod assemblies. You need opposite threads on each end so that turning the tie rod or turnbuckle adjusts the length without disassembling the whole thing.

 

[dtimberlake]

I think fuel gas fittings are often LH thread.

 

[LittleWheels]

Precession is the behaviour that drives left-hand threads in some applications.

Everyday Scientist » why is the left bike pedal left-hand threaded?

As EdStainless noted, a chamfered interface overcomes precession. This solution was promoted by Jobst Brandt back in the day.

Left Hand Threads on Bicycles by Jobst Brandt

Article by Jobst Brandt about left-hand threading on bicycles

sheldonbrown.com

 

[rb1957]

when to use a LH thread ? When a RH thread won't work (like on a joint subject to RH rotations).

when to use a LH thread ? When, as a LH (or RH ?) designer, you want to mess with the RH world ...

 

[Prometheus21]

Like dtimberlake mentioned; fuel gas fittings often have LH threads; like most cylinder valves meant for flammable mixtures. But I have also seen a M19x1.5 LH thread on a nitrous oxide cylinder at an offshore facility once; wheras the rest of the industry uses RH threads...

 

[Denial]

Regarding dtimberlake's comment #14 above, the use of LH and RH threads in gas fittings is for an entirely different purpose. When I was learning oxy-acetylene welding, it was explained to me that (after both gas cylinders had been attached to the welding torch) you turned on the oxygen first, ignited it, then gradually turned on the acetylene. If you reversed the attachment of the bottles you would light the acetylene first. This was a mistake that NOBODY could make twice.

 

[Prometheus21]

LH threads are also a great way to make Joe the Homeowner think twice before using the equipment.

Oxygen is not flammable; just an oxidizer. Cutting torches are supposed to be ignited using pure acetylen; possibly with a very small amount of oxygen to avoid bothersome soot. You then adjust the flame characteristic to whatever purpose using the preheated oxygen valve. In cases of persistent blowbacks howevever you would ALWAYS close the oxygen valves first.

 

[Loco_]

Thanks all. Awesome I was busy and had just read all the messages.