Can pressing on a screw generate torque?

[titanan]

Today I and my physics teacher argued about that. I think that in optimal conditions applying force to the top of a screw can turn it and generate torque. ( On a surface) Can you please answer and send an article that mentions that? Because i wasn't able to find one. Thanks already and sorry for my bad English.

 

[Nugatory]

I don’t know of any articles explaining the principle, but a manual impact driver does what you describe and there are also children’s toys that work that way.

So I’d say that you are right.

 

[anorlunda]

You have probably seen switches like this. Press to turn on. Press again to turn off. The presses rotate a switch inside.

 

[pbuk]

I don’t know of any articles explaining the principle, but a manual impact driver does what you describe and there are also children’s toys that work that way.

So I’d say that you are right.

In case there is any confusion, the impact driver works by applying the force of the hammer blow to an internal thread that has a very long pitch.

It is not possible to turn a screw with a thread designed for holding in a material by applying an axial force to the screw because of friction between the thread and the material. Any axial force increases this friction. If the friction were not there then the screw would unscrew of its own accord.

 

[256bits]

Worm gears ( which is a type of screw drive ) utilize the principle of being self locking or not.
You might be able to find some information by looking that up.
From Wiki just a brief

Unlike with ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible when using large reduction ratios. This is due to the greater friction involved between the worm and worm-wheel, and is especially prevalent when a single start (one spiral) worm is used. This can be an advantage when it is desired to eliminate any possibility of the output driving the input. If a multistart worm (multiple spirals) is used then the ratio reduces accordingly and the braking effect of a worm and worm-gear may need to be discounted, as the gear may be able to drive the worm.

Worm gear configurations in which the gear cannot drive the worm are called self-locking. Whether a worm and gear is self-locking depends on the lead angle, the pressure angle, and the coefficient of friction.

Any normal fastening screw would have to be self locking to be useful in the material it is being used, so by the application of just an axial force to it would not loosen the joint, as explained in previous post.

 

[titanan]

In case there is any confusion, the impact driver works by applying the force of the hammer blow to an internal thread that has a very long pitch.

It is not possible to turn a screw with a thread designed for holding in a material by applying an axial force to the screw because of friction between the thread and the material. Any axial force increases this friction. If the friction were not there then the screw would unscrew of its own accord.

So if there was no friction between the screw and the surface, when we would turn the screw upside down it would fall. And naturally, it would turn while falling. So gravity pulled it, not turned it but the screw turn. Wich was what we were trying to find out.

 

[tech99]

I think this is just a case of a mass sliding down a ramp.
If the Coefficient of Friction is greater than the tangent of the slope angle then it does not slide.

 

[jrmichler]

I think that in optimal conditions applying force to the top of a screw can turn it and generate torque.

You are correct. It does not need optimal conditions, merely a combination of large enough lead and low enough friction. Conventional screws rarely will do this, but it's common with ball screws. Here is a good discussion of reverse efficiency from THK, a major manufacturer of ball screws: https://tech.thk.com/en/products/pdf/en_b15_006.pdf.

 

[titanan]

You are correct. It does not need optimal conditions, merely a combination of large enough lead and low enough friction. Conventional screws rarely will do this, but it's common with ball screws. Here is a good discussion of reverse efficiency from THK, a major manufacturer of ball screws: https://tech.thk.com/en/products/pdf/en_b15_006.pdf.

Thank you very much. That was exactly what ı was looking for.

 

[A.T.]

I think that in optimal conditions applying force to the top of a screw can turn it and generate torque.

I had this as a kid. You push on the plunger to spin the bottom part. But if the spinner is fixed while the plunger is free to rotate it will rotate, because there are equal but opposite torques. Note the high thread pitch.

You have probably seen switches like this. Press to turn on. Press again to turn off. The presses rotate a switch inside.

View attachment 275006

Similarly in retractable ball pens:

 

[jbriggs444]

It has been a while, but if you lube up a drywall screw I seem to recall that you can get them to twist themselves in with a pure push. They are double-threaded (two threads in an interlaced helical pattern) so the pitch is twice as great as a conventional thread for a given thread spacing.

 

[sophiecentaur]

Summary:: Can we generate torque by pressing to a screw?

Today I and my physics teacher argued about that.

My pet hate is people's inability to use the term Mechanical Advantage when they should be using Velocity Ratio. Velocity Ratio relates to the geometry of a situation (pitch of a screw or the way pulleys are arranged), whereas Mechanical Advantage tells you the actual ratio of Effort applied over Load force obtained.
In an ideal world MA/VR is unity and in an ideal world all your screws would fall out of the wall. Screw fixings work because Efficiency (MA/VR) is always <1. Friction is your friend more often than you care to admit.

I wonder if they sell as much WD40 as Superglue.?

Merry Christmas.

 

[Keith_McClary]

Screw-shank nails, sometimes referred to as spiral-shank nails, turn as they are driven into wood. This threading action increases frictional force within the wood and leads to a greater withdrawal strength under less-than-optimal conditions.

Use them for: Squeak-free hardwood flooring and decking, siding, or in framing assemblies susceptible to high winds and moisture.

Raysonho @ Open Grid Scheduler / Grid Engine

 

[Lnewqban]

 

[A.T.]

 

[sophiecentaur]

@Lnewqban
The Yankee Screwdriver. A blast from the past. Older UK members will remember Barry Bucknell, the pioneer TV DIY presenter. Anyone who saw him assembling his shelves and fittings desired one of those screwdrivers. Iirc, they were quite expensive and I'm sure you'd need to be pretty competent to be able to make use of one.
Thank heavens for Lithium Ion Batteries!

 

[jrmichler]

My Yankee screwdriver is easier to use than a conventional screwdriver, and is one of my prized tools. I prefer it to an electric driver because I get better control, especially with small screws. My Yankee push drill gets used only occasionally.

 

[Richard R Richard]

I think that in optimal conditions applying force to the top of a screw can turn it and generate torque.

Screwdrivers with helix guides generate torque by pressure, but I think the question, if my translator works well, refers to the torque being created by the screw itself.
Applying torque with the screwdriver is what makes the screw penetrate. In other words, the thread generates axial impulse, from a torque. And the opposite is also true.
When pressing the screw, it penetrates the base material, then the friction of the thread creates torque in the sense that the screw head rotates with the pitch of the thread.
But of course, this is not very useful in practice and therefore, by design of the screws, they have a thread angle for which the torque necessary to insert it into the material is much higher.
As already explained previously in the thread, this is necessary so that the screw does not escape again when trying to pull back from the head.
Therefore a normal screw when pressed into the material should neither insert nor rotate, otherwise the fixation is not secure.
So, if the screw manages to penetrate the material, the friction between the surface of the thread and the material, “does create torque”, this is precisely what is necessary to overcome to introduce the screw into the material.

 

[Nugatory]

Screwdrivers with helix guides generate torque by pressure, but I think the question, if my translator works well, refers to the torque being created by the screw itself.

A shaft with a helical thread cut in it IS a screw.

The threaded fasteners called "screws" are a special case, designed with a thread pitch that makes it difficult to rotate them by applying axial force (but not impossible - see @jbriggs444 post #11 above) because otherwise they wouldn't be very good fasteners. But there ar more kinds of "screw" than that.

 

[jrmichler]

Some screws are not supposed to back drive, but do anyway. I have a pair of hand screw clamps with double lead screws. The screws are 3/8" diameter. The threads look like 16 threads per inch, but have 1/8" lead (8 turns per inch of travel). After I lubricated the screws to stop them from squeaking, the clamps stopped clamping. I tighten the clamp, and the screws unscrew by themselves. Not enough friction to work correctly.

I tried to clean off the lubricant with solvent, but have had only partial success. The clamps will hold, but with only light clamping force.

 

[artis]

Use them for: Squeak-free hardwood flooring and decking, siding, or in framing assemblies susceptible to high winds and moisture.

Raysonho @ Open Grid Scheduler / Grid Engine

Wow did not know these existed, cool.

I guess with these nails the saying "to nail someone" finally gets justice.

 

[sophiecentaur]

friction between the surface of the thread and the material, “does create torque”,

To take the situation to an extreme, you could imagine a screw being pushed through a very low viscosity fluid. The friction wouldn't be primarily responsible for any force / torque but transfer of Momentum from helix to fluid would generate a torque. OR you could consider a machine screw being pushed through an already cut thread. There would be a torque, generated not by friction but by (cause and effect??) the angular acceleration of the screw.
N3 always applies in this sort of situation.

 

[Richard R Richard]

The friction wouldn't be primarily responsible for any force / torque but transfer of Momentum from helix to fluid would generate a torque...
N3 always applies in this sort of situation.

A shaft with a helical thread cut in it IS a screw.

The threaded fasteners called "screws" are a special case, designed with a thread pitch that makes it difficult to rotate them by applying axial force

Hello, @sophiecentaur and @Nugatory
I'm sorry I can't interpret or understand your words better, my knowledge of the English language is not good enough for it. I trasnlate you by google. Do you agree or disagree with what I stated in message # 18?

The best example that an axial force on any propeller can be converted into torque is a wind power generator, or a hydroelectric power plant turbine, that the material is a solid such as wood, plastic, sheet metal, etc. instead of a fluid, not it influences the physical principle that makes it possible.
Take a photo after each hammer blow on the nail head of message # 21, and you will see how a small angle rotates as it penetrates the material, there is a linear relationship between the impact force and the rotated angle, the variables are the coefficient of friction and the angle of the thread.

 

[sophiecentaur]

I'm sorry I can't interpret or understand your words better,

Here it is again in short form: You do not need friction to produce a couple (efficient turbine). You do not need torque to penetrate a solid (Nail). A screw will usually turn because of the driver. N3 tells us that there are equal and opposite torques always involved.

A woodscrew, first time it's inserted, will present a lot of friction and also forces needed to part / distort the material on the way through - not only the friction, as you are implying.

Imo, one should be careful in trying to say what's really happening in any complex bit of mechanics. All the major factors have to be identified and quantified first. Sometimes all but one can be ignored but I don't reckon that applies with a wood screw (or any self-tapper).

 

[hutchphd]

I don’t know of any articles explaining the principle, but a manual impact driver does what you describe and there are also children’s toys that work that way.

In case there is any confusion, the impact driver works by applying the force of the hammer blow to an internal thread that has a very long pitch.

In fact most of the time I have used an impact driver to remove recalcitrant screws. Honda motorbikes had some terrifying phillips-head machine screws.

 

[DaveC426913]