Speaking of home wood-related repairs...

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So? Lots of people thing screwing is fun.
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There are no stupid questions, but there are lots of stupid answers.

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
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On 10/06/2009 11:43 AM, Joe AutoDrill wrote:

Nails are cheaper.
A properly heat-treated screw is about as strong in shear strength as a nail the same size as the shaft, but is stronger in pull-out.
There are comparatively few screws that are actually rated and approved for structural applications.
Chris
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Why a heat treated screw? Nails are dead soft.
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CW wrote:

Tru dat. A standard framing nail has a shear streangth of something like 16,000lbs. A screw designed for strength (like a cabinet screw, not a drywall screw) is probably a 1/3 that.
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-MIKE-

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like 16,000lbs. <<<<<<
First comment; some (many) nails are dead soft but not all nails are dead soft.
Huh? Care to take another try?
Do you mean the nail material has an allowable shear stress of 16,000 psi (lbs / sq in) ?
Because the code allowable shear loading (last time I checked) for a 16d common is somewhere in the 150 lb range
so........ your units are off, your concept is wrong or your number is off by 100x.
cheers Bob
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fftt wrote:

No. I mean it takes 16,000lbs to shear a nail.
Have you seen those tests they do with the giant machines that hold piece of whatever in one jaw while the other jaw pushes or pulls or tears the other end. This shear test has both jaws right next to each other, coplanar, while one jaw moves down, perpendicular to the length of the nail.

I'm guessing that has to do with how much weight is allowed, by code, to be held by a single nail. That has nothing to do with the shear strength limit of the nail. If the two were the same, then every house would collapse before finished.
You and I can exert much more than 150lbs with our bare hands.
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-MIKE-

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-MIKE- wrote:

A 16d nail has a nominal diameter of .162 inches. That gives an area of about 0.02 inches.
To get 16,000 pounds out of that area would require steel that could take a sheer stress of 800,000 psi. This is beyond the range of even exotic ultra high strength steels, let alone the the cheap junk that is typically used in modern nails. For a typical mild steel the shear strength woulde be around 60,000 psi, so multiply that by .02 and you have 1200 pounds.
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J. Clarke wrote:

I don't get what psi has to do with anything. You put half a nail in a clamp, the other half of the clamp moves down with the weight of 8 tons. That is well within many testing machines. They test steel beams and concrete sections way, way, beyond that weight.
IN ANY CASE, this irrelevant detail has nothing to do with my original point that a nail is many, many, many, many times stronger that a fu@&!ng screw! forest, trees? hello? anyone home?
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-MIKE-

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Lighten up, Mike. You're talking about relative strengths, which inherently incorporates the differing material properties. It is not an irrelevant detail to correct an obvious error in shear strength, as this is what we are talking about, and shear strength is figured in PSI, which incorporates the area. It is not a question of whether a testing machine can exert such force, it is a question of whether the item being tested has the material properties to withstand that force.
Your point that a common nail is stronger in shear than a drywall screw is not coming under fire. It is the 16,000 lbs thing. Here's a little video for you to back up your point: http://www.metacafe.com/watch/967794/shear_strength_of_nails_drywall_screws_construction_screw /
As an aside, the malleability of a framing nail goes a long way to contributing the long term strength, and longevity, of a structure. I'm sure you've seen framing where the pieces have pulled away a bit, the nail has bent a bit, but it is still firmly embedded in the wood pieces. A framing screw has no such give and will be more likely to split the wood when the building inevitably begins to move.
There are many reasons to use screws, but there are also reasons not to.
R
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RicodJour wrote:

I still swear I've seen that number and it surprised the crap out of me, too. I've been looking through some of my textbooks and publications, but don't have any more time to look.
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-MIKE-

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I've been looking through some of my textbooks and publications, but don't have any more time to look.<<<<<<
Mike-
Your recollection is wrong...we all make mistakes.
Your 16,000 lb number is nonsense, please don't continue to quote unless oyu can cite it.
You can take all the time in the world...you;re not going to find a shear strength of a 16d nail to be 16,000 lbs...ain't gonna happen.
cheers Bob
ps I agree that often nails are much stronger than screws and as Rico noted there are times to use each.
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So... You're saying nails and screws shouldn't be used in forests or trees due to them being ... what? <G>
Seriously though, I got your point about nails being stronger than screws. It has a lot to do with the fact there are grooves in a screw.
As a machine builder, I know all to well that the weakest point on a shaft or spindle is almost always where there is an undercut or snap ring groove, etc. You'd be amazed at how often something fails because a machined sharp angle or right angle is there on a steel or aluminum part instead of a machined curve of some sort.
Screws have lots of these stress points and thus break more easily. However, they do avoid coming loose with vibration, are more easily used to "suck" parts tight and all that jazz.
The strength of nails is way beyond what almost any home engineering job would need. If you don't believe me, drive some small finishing nails deep enough to be 50% in one piece of strong wood and 50% in the other... Maybe use two or three at most. Now try to "sheer" the nails by whatever manual method (toolless) you can think of. I bet they bend and come loose before you break any of them unless you bend them back and forth.
The screws will be even harder to break because you won't be able to work them loose by hand in most cases.
So... Depending on where you live, what you need the fastener for, etc. determines which to use. Personally, I like doing things the "right way" the first time which means the quality way even if there is some loss or waste.
Would I build a farm fence with screws? Probably not. Would I build a deck with nails? Probably not except for maybe the framework - but even then, I'd probably opt for screws here in NJ where we get hot, cold, wet, dry and generally a lot of traffic.
Just for grins... Let's assume your screw is similar to a 1/4-20 threaded bolt... That bolt, in the cheapest grade often used has a maximum weight bearing capacity of 2350 lbs. The suggested limit is lower because of vibration and other movement and is generally recognized to be around 200-300 lbs. That means a man my size can hang from a 1/4"-20 bolt all day long and pretty much move around all I want.
A 1/2" bolt is approximately 450% stronger on average.
Now, let's presume the screw's shank is 1/8" diameter and similar in quality to the Grade 2 bolt... That means that it is probably capable of holding 500 lbs or so with a safety rating of around 40-50 lbs.
Given the fact that screws are not machined out of quality materials, I'd divide those numbers by two for the average steel screw. The numbers will be slightly higher for a nail as there are no grooves.
This is all based on average quality bolts (Grade 2). Grage 5, Grade 8 and even higher grades for aircraft use, etc. are significantly stronger with a 1/4" bolt sometimes having a weight bearing capacity near 10,000 lbs.
Bottom line? Unless you are using big fat "gutter nails" made of steel, you're not going to have a 16,000 lb. shear limit on the average nail.
What trees? What forest?
Regards, Joe Agro, Jr. (800) 871-5022 01.908.542.0244 Automatic / Pneumatic Drills: http://www.AutoDrill.com Multiple Spindle Drills: http://www.Multi-Drill.com Production Tapping: http://Production-Tapping-Equipment.com / Flagship Site: http://www.Drill-N-Tap.com VIDEOS:
http://www.youtube.com/user/AutoDrill

V8013-R
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More to do with what's done to the steel during manufacture. The drywall screw is hardened and thus brittle.
R
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-MIKE- wrote: ...

Then you don't understand what shear is all about...
<http://emweb.unl.edu/NEGAHBAN/Em325/13-Shear-stress-in-beams/Shear%20stress%20in%20beams.htm
consider the nail to be a small-diameter round beam.

SO???
I don't follow what you're trying to describe, anyway, and sounds like perhaps you're confusing tensile strength w/ shear...

How do you reach that astounding conclusion in general?
The relative strength of a nail and a screw will depend on their relative sizes and the material of which each is made and has little, if anything, to do w/ the difference between simply being a nail or screw...
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dpb wrote:

How?
Drive a common 16d nail 2/3 into a 2x4. Do the same with a common screw of the same diameter shaft.
Take sledge hammer and swing it directly down on the nail. It will bend. Do the same to the screw. It will "shear" right off.
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-MIKE-

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On 10/09/2009 02:39 PM, -MIKE- wrote:

That's why I specified "properly heat-treated". The heat treatment keeps it from being brittle due to work-hardening from rolling the threads.
Just for fun, I tried your experiment with a #10 Spax brand exterior screw. (Lee Valley carries them.) The screw bent. I then pounded it back straight and removed it with a power driver.
I then tried it with a #10 "Precision" brand decking screw from Home Depot. The screw snapped.
Chris
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-MIKE- wrote:

You're confusing impact strength with shear strength.
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J. Clarke wrote:

I'm not. It relates enough to get the point across.
I've seen the tests, I've sat through the lectures.
bye
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-MIKE-

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-MIKE- wrote:

Yes, you are. You may think otherwise but what you think and what is true are not necessarily the same. When you hit something with a hammer you are testing its impact strength--this is exactly the technique that is used in the laboratory, with the velocity and mass of the hamner and the point of contact carefully standardized (your experiment does neither). When shear strength is measured a steady load is applied.
If you know anything about metallurgy you'll know that when you harden steel you increase its tensile and shear strengths and reduce its impact strength.
When you talk about "shear strength" you are using a technical term which has a specific meaning, and the test that you describe does not measure that quantity no matter how mucg you may want it to.

What tests and what lectures?
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Mike-
If these tests & lectures were involved in process that lead to a technical degree (physics or engineering)....please let me know so I can notify your alma mater to begin the "degree recall process".
You have, in the later part of this thread, violated "the first rule of holes"..........which is "stop digging".
shear & impact tests are used to determine different properties....
btw find that 16,000 lb number yet?
cheers Bob
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