Threads on screws

Hi,

Possibly a silly question.

I'm told the threads provide most of the holding power of a screw. 

Ice has different strengths at different depths, so why don't ice screws have threads extending their whole length?

This might help if the inner ice was less good, and reduce the need for removing screw then fumbling for a shorter screw?

The additional weight would be tiny. 

I agree that more threads are better!

My thought is that after you get to a certain length, the threads vs. more holding power is negligible, thus why there is a same thread length on say a BD 13cm and a BD 16cm screw.  

Point of curiosity: Does anyone have a source of data that backs up the claim that threads are where the holding power comes from? 

Though I agree that treads can be important--especially when the hanger is lower than the tip, I have some vintage US armed forces ice pitons that have no threads. They work great for fixing jug lines, but you can't unscrew them, so must chop them out or leave them behind. Not so practical, which is why they probably went out of style 70 years ago. But they work just fine as long as they go in at an angle; they won't work at all in a roof. But I have confidence that the force at which the ice breaks for a screw placed perpendicular to the ice surface is proportional to the length of the ice screw times the diameter. I have good data on that somewhere.

I'm going to GUESS that the threads add surface area and that full length screws get extra hard to screw in when the ice is under compression and/or when the ice freezes to the ice screw.

This is worth looking at for anyone who hasn't seen it. A little dry, but it shows the strength of various screws and threads and positions of screws in the ice. If i remember correctly they touch on the strength being in the screws too.

https://youtu.be/Cr8nVnXqvts

"Dynamic Shock-Load Evaluation of Ice Screws:  A Real World Look", by Marc Beverly & Stephen Attaway:  fifteen page exposition of engineering/testing performed at  the ice park at Ouray Colorado circa 2016.  The complete paper is online for your reading pleasure

-Haireball

Double J wrote:

My thought is that after you get to a certain length, the threads vs. more holding power is negligible, thus why there is a same thread length on say a BD 13cm and a BD 16cm screw.  

Hi. That I think assumes that the threads are in the good ice, whereas the deeper ice might not be so great 

I would buy ice screws that are threaded along their entire length, if they were available, for the reason mentioned by the OP.

The safety certification testing that is done for ice screws isn’t really representative of realistic worst case conditions in chandelier ice.  So, while a shorter threaded length can achieve the >5kN pull out strength requirement in ideal conditions, this is not necessarily true in chandelier ice (which contains air pockets).

My educated guess is ice screw manufacturers are simply reducing the thread length to the minimum required to meet the requirements of EN 568.  It seems like ice screw manufacturers are more interested in competing on weight, cost, or ease of placement than holding power in realistic worst case conditions.

Karl Henize wrote:

I would buy ice screws that are threaded along their entire length, if they were available, for the reason mentioned by the OP.

BD made some ultralights for Will Gadd that are threaded all the way up. You can see them in his 9 part video series.

Edit - if BD were truly interested in differentiating their products, they'd do this on all their longer aluminum screws. No real downside, and they'd be better poised to compete with Petzl's (arguably superior) lightweight screws.

Gunkiemike wrote:

BD made some ultralights for Will Gadd that are threaded all the way up. You can see them in his 9 part video series.

Thanks, I'll drop The Man an email

dave custer wrote:

Point of curiosity: Does anyone have a source of data that backs up the claim that threads are where the holding power comes from? 

Though I agree that treads can be important--especially when the hanger is lower than the tip, I have some vintage US armed forces ice pitons that have no threads. They work great for fixing jug lines, but you can't unscrew them, so must chop them out or leave them behind. Not so practical, which is why they probably went out of style 70 years ago. But they work just fine as long as they go in at an angle; they won't work at all in a roof. But I have confidence that the force at which the ice breaks for a screw placed perpendicular to the ice surface is proportional to the length of the ice screw times the diameter. I have good data on that somewhere.

I'm going to GUESS that the threads add surface area and that full length screws get extra hard to screw in when the ice is under compression and/or when the ice freezes to the ice screw.

When placing ice screws, you want them angled downward to engage the threads not angled upward to use the structure of the ice (this creates a moment between the screw and the outside surface of the ice that supports the screw which is weak) which breaks at around 4kn. Changing the angle to between perpendicular and 15° downward can DOUBLE the holding power, relying on the structure of the ice for each thread rotation while creating a weaker moment. You can think of it in components of a fall and load distribution along the screw. A screw perpendicular or angled up will see the entire force on the very outside of the screw where it meets the ice (if flush) whereas a downward angled screw will have that downward load applied to all the threads as well. This amount depends on the angle if the screw but it is equal to the magnitude of the force times the sine of the angle. [Force on the threads=| Force of the fall |*sin(angle of the screw) in the direction of the screw]Testing by manufacturers determined that the ideal angle to maximize thread strength and the torque strength of a screw is about 10-15° below perpendicular. Above perpendicular completely loses the strength of the threads. 

David,

I don’t have any concrete answers to your question.

I have attached a photo from the book ”The Art of Ice Climbing” published by Blue Ice (2012).

When loaded, and the ice screw experiences a bending moment, does the absence of threads in the “A” zone (where the ice is usually weaker) make the screw more secure? (i.e. would threads here damage the ice more than no threads?)

Hope you find a more definitive answer.

Marty C wrote:

David,

I don’t have any concrete answers to your question.

I have attached a photo from the book ”The Art of Ice Climbing” published by Blue Ice (2012).

When loaded, and the ice screw experiences a bending moment, does the absence of threads in the “A” zone (where the ice is usually weaker) make the screw more secure? (i.e. would threads here damage the ice more than no threads?)

Hope you find a more definitive answer.

I recall an article (BD Labs ?) which stated that when the thread went all the way to the end, the placement became weaker. The screw shaft was stiffer thereby exerting more leverage.

The conclusion was that you want the shaft to bend.

I wish they didn't close the BD labs page. So much good information there.

One more reason that comes to mind is if your screw bottoms out. You don’t want to clip the hanger if the screw protrudes more than 5cm out from the ice, it multiplies the moment generated on the ice. Better (not by that much, best is a shorter screw) is to hitch a sling to the shaft. This might be the best reason why long screws only have 12cm of threads. Especially because 12cm of threads is really good enough. 

Gunkiemike wrote:

BD made some ultralights for Will Gadd that are threaded all the way up. You can see them in his 9 part video series.

Edit - if BD were truly interested in differentiating their products, they'd do this on all their longer aluminum screws. No real downside, and they'd be better poised to compete with Petzl's (arguably superior) lightweight screws.

I think those were prototypes.

 The tying off of screws that don't sink all the way in has been addressed by testing to prove that it does not work. screw bends over and  sling cuts on hanger.  this has been adressed by salewa and perhaps others? they have screws with slings attached to the shaft with metal ring that can be positioned for proper depth???   i seriously doubt other manufacturers  limited the length of the threads  with tying off in mind. i suspect it has something to do with ease of placement or placement strength or manufacturing cost.  

Nick Budka wrote:

One more reason that comes to mind is if your screw bottoms out. You don’t want to clip the hanger if the screw protrudes more than 5cm out from the ice, it multiplies the moment generated on the ice. Better (not by that much, best is a shorter screw) is to hitch a sling to the shaft. This might be the best reason why long screws only have 12cm of threads. Especially because 12cm of threads is really good enough. 

Threads would help keep slings from slipping towards towards the hangar.  I think a fully threaded screw is still preferable in this scenario.  

David Coley wrote:

Hi. That I think assumes that the threads are in the good ice, whereas the deeper ice might not be so great 

How often do you come upon the deeper ice being rotted in a true water ice scenario,  serious question? 

I have always found the better ice under the outer layer

Karl Henize wrote:

I would buy ice screws that are threaded along their entire length, if they were available, for the reason mentioned by the OP.

The safety certification testing that is done for ice screws isn’t really representative of realistic worst case conditions in chandelier ice.  So, while a shorter threaded length can achieve the >5kN pull out strength requirement in ideal conditions, this is not necessarily true in chandelier ice (which contains air pockets).

My educated guess is ice screw manufacturers are simply reducing the thread length to the minimum required to meet the requirements of EN 568.  It seems like ice screw manufacturers are more interested in competing on weight, cost, or ease of placement than holding power in realistic worst case conditions.

Wouldn't you change location or screw length if you hit a air pocket or bad spot? 

If its free standing chandelier Ice I personally wouldn't want a screw in it anyway. 

Chris M wrote:

Wouldn't you change location or screw length if you hit a air pocket or bad spot? 

If its free standing chandelier Ice I personally wouldn't want a screw in it anyway. 

Sometimes.  It isn’t always practical to change the location or length of a screw.  Quite frequently, the most practical thing to do is place a second screw from the same stance or climb a short distance above your bad placement in the hope of finding better protection.  If the quality of ice is bad throughout, then you will generally want to place screws more frequently or equalize them.  

Marty C wrote:

David,

I don’t have any concrete answers to your question.

I have attached a photo from the book ”The Art of Ice Climbing” published by Blue Ice (2012).

When loaded, and the ice screw experiences a bending moment, does the absence of threads in the “A” zone (where the ice is usually weaker) make the screw more secure? (i.e. would threads here damage the ice more than no threads?)

Hope you find a more definitive answer.

To the original post person; yes. this was a good question

My guess on this matter is that the threads kind of become a focus point for any stresses applied.

On the smooth part of the screw forces will be spread over an area, whereas on the threaded part the forces will be on a couple/few threads.

And being that the threads are a pitched screw, the forces will be focusing on a slight diagonal, which I believe will increase the bending effect.