I have been engaged in an online debate about the merits of screws compared to nails when fastening metal to wood, such as with Simpson connectors. During this debate, a couple of ideas have been introduced that some of you may shed some light on.
1. Nails must be driven into wood with a minimum of blows to ensure a better hold from the wood. Example: A 16d nail when driven with three hammer blows will hold better than one driven by either a palm nailer or an inexperienced carpenter who taps them in with 10 blows.
2. The holding power of a nail is proportional to the wood it displaces, therefore pre drilling a hole will reduce the hold from the wood. (Assume the pre drilled hole is 75% or less of the diameter of the nail). Example, a 16d nail driven into a hole pre drilled to 7/64 will have less hold from the wood than one that has been driven into wood with no pre drilled hole.
On this question, someone quoted the following as a retort:
From “Understanding Wood” by Bruce Hoadley, p 189:
“The fact that nails can be driven without pre boring pilot holes has apparently led to the assumption that they should be driven without pre boring. An unfortunate corollary seems to be that nails are therefore limited to use where they can be driven without splitting the wood or bending over. In reality, the best holding power results when nail holes are pre bored [Emphasis added]. While most woodworkers accept the idea of installing wood screws in purebred holes to prevent splitting and to maximize holding power, they seldom consider pre boring nail holes.”
Is there any new information on this topic beyond what Bruce Hoadley wrote, or is there disagreement with his words?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Replies
I'm no expert, but here's my 2 penny:
On point one, what are the reasons that the number of blows would make any difference whatsoever in holding power? Are their physical properties of the steel or wood that are changed by the number of blows? Is the physics of the hole (holding power) created in one manner different from the hole created in the other? I can't imagine this makes a bit of difference. The same amount of work is being done with the same end result being achieved. This sounds like some macho carpenter/framer urban legend - the guys swinging the 22 ounce hammers teasing the apprentices with their 16 ouncers or some such.
On point two, I often predrill nail holes on things like trim and whatnot to prevent splitting and related problems. They hold just fine. And I can imagine that a predrilled hole might, in fact, hold better because the nail would be compressing the wood at the full diameter of the undersized hole with no splitting action, whereas a nail driven into the wood without a pilot might tend to split the wood and break more fibres such that it is only being held by the wood from two sides of the split grain.
In the end, if you are not talking about specific applications - i.e., achieving hold in a given species, in a given circumstance (tacking or joining, for example) with a specific type of nail - you're largely arguing about the number of angels that can dance on the head of a pin.
And who would care if the hold is technically "stronger" if half the time you split the wood you are trying to hold when you try to make this "strong" bond. LOL
Yes, everything you said was what I was thinking.
It may seem like Angles dancing on the head of a pin, but these ideas are what are being used to discredit some tests I did that the framers aren't liking the results of.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
"It may seem like Angles dancing on the head of a pin, but these ideas are what are being used to discredit some tests I did that the framers aren't liking the results of."
Paul,
I've read the thread over on Breaktime and, quite frankly, I'm really disappointed that this nonsense has migrated over to Knots.
If you really believe that it's possible for you to accrue more credibility than the seasoned professional homebuilders who share their expertise over on Breaktime by continuing to flog this dead horse in the futile hope that a miracle will occur and it will somehow cross the finish line in first place, I have but one question to ask: What color is the sky on your home planet?
Please - give it a rest,-Jazzdogg-
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." Bertrand Russell
Well, before he "gives it a rest" I'd still like to know what his point is.********************************************************
"I tend to live in the past because most of my life is there."
-- Herb Caen (1916-1997)
Nikkiwood,
If you're interested, you can check out the ongoing rant over at Breaktime.
-Jazzdogg-
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." Bertrand Russell
I did read part of that thread, but I'm way to lazy to go back there for another look. I'd rather have him tell us here why he is so possessed with this issue. It's been awhile since someone brought up an issue that was so profoundly irrelevant as this one. But then again, maybe I am missing something -- so await, with bated breath, for his explanation.********************************************************
"I tend to live in the past because most of my life is there."
-- Herb Caen (1916-1997)
About the strength of nails vs screws or whatever: Most often when I use a nail, my main concern is shear (except for temporary holding power when gluing). Screws are designed for tension but I don't rely on them overly so for woodworking. Comparing the strengths of the two in shear, my money is on the nails. I don't think it is a good idea to use screws for joist hangars for instance, where shear strength is important.
Hi Nikkiwood,
If it's OK with you, while you're waiting with baited breath to hear why someone with limited knowledge and extraordinary tenacity is tilting at windmills and attempting to swat flies with a sledgehammer (despite the fact that he's an adamant proponent of screws), I'll go carve some walnut ; - )
What's the old saying? "Never try to teach a pig to sing; it wastes your time, and annoys the pig!"
Hey, let me know if anything remotely related to fine woodworking is discussed, will ya?
-Jazzdogg-
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." Bertrand Russell
Hi guys!
are you comparing wire nails or the old cut nails? ( rectangular or square cut nails) I find them harder than wire cut nails, they also cut the grain preventing splitting and giving them more holding strength.
I just wanted to ask.
C.A.G.C.A.G.
Amen--- brother. This here post is pure hogwash. Who on God's green earth (or at least in Knots gives rat's toenail about nail strength? The post was at first amusing now just boring. Think I will stop proliferating the post now.
While you are carving walnut, i am going to mill up some cherry.
Later-
MarkoThank you,
The Great Marko
your point about predrilling is a good one for "interfibrous friction fasteners." At a certain point the nail can reach its "moment" when it will release as with a puller attached to it. I find the nails set tightest when a minimum number of blows are applied to the head. The question then is at what point does the predrilling affect the hold or release point of the nail or conversely the force necessary to drive the nail through the fibers. And isn't this why some woods don't hold nails well. Fir and hem/fir are the best nail fastened woods in my experience. What do the rest of you think and more importantly does anyone have an engineer viewpoint on this. Aloha, mike
I'm with Samson on both points.
I think he hit the nail on the Head!
Interesting question but it would generate better interest in Breaktime as it's emphasis is on house building. I haven't used a Simpson strong tie on furniture yet but perhaps someday. We do use them in our Timber Framing Shop.
Well, this question was generated in Breaktime. However, since there is a different approach here to wood and fasteners I thought this would be a better place to get some input on these theories.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
My Encyclopedia of Wood, chapter 7 has 29 pages on this subject. Forgive me if I seem lazy for not typing them all out for you. If you would like to take it further than that there are 40 listings on the reference page for this chapter. Most of them refer to the Forest product Laboratory if you would like to really get a thorough answer you may want to read some of them.
There are so many variables to be considered here that without being very very specific in all descriptions, it will be hard to compare apples to apples. However, I do not think the following is true. (Nails must be driven into wood with a minimum of blows to ensure a better hold from the wood.) When I was a framer, I could drive 16d nails all day with one stroke, however I can not slowly exert enough force with the same hammer without swinging it. Also, I find that it is easier to pull fasteners with a quick jerk than with a slow pull, and I can not tell any difference between extra blows and pull strength. However there may be some with cement coated nails.
My book says there is no difference between power driven nails for strength with hand driven when all other factors are the same.
As far as other factors such as size of hole relative to fastener size would make a huge difference when it comes to extraction. For instance a nail driven into a hole the same size as the nail would be easier to pull than one in a hole 25% smaller. However they may both have the same shear strength which is more closely related to the compression perpendicular to the grain of a given species.
As far as agreeing with Dr Hoadly, yes that is correct, but if you are going to go to the trouble to drill a hole, the screw will have more holding power because of the mechanical bite of the threads. If you can drive your nails faster by drilling pilot holes, then that is how you should do it. I however can not come close.
Thank you for that source material, I'll take a look for it.
I agree with using the screws, but the credibility of one of my tests was called into question because I pre-drilled a toenail connection to avoid splitting out the end grain.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Here is a link to FPL where you can download a pdf.
http://www.google.com/search?client=safari&rls=en-us&q=fpl+tech+note+243&ie=UTF-8&oe=UTF-8
There are others besides this.
When a nail is hit into a piece of wood, the wood fibers are bent down in the direction of the nail. These downward facing fibers cause the friction on the nail that prevents it from coming out. Technically a nail is not a mechanical device, such as a screw, it uses friction to hold it in place, not threads. (this is not true for any nails with ridges or a coating, these qualities may make a nail a mechanical device.)
Regarding point #1, if a nail is pounded into a piece of wood with only 2-3 blows, there may be little damage to the surface of the downward facing wood fibers. Thus, increasing the coefficient of friction. When a palm nailer is used, the nail rubs against the wood fibers hundreds of times before it's all the way in. This may be causing something like a burnishing effect on the wood fibers and the coefficient of friction is severly compromised.
I can't help on #2, I'm still thinking about this one.
Keith - you also mention that it's easier to pull out nails with a quick pull. This has to do with the two different forms of friction - kinetic and static. Static friction is the friction you experience when you try to move something from a stand-still. Kinetic is the friction to keep an item going when it's already moving. Static friction is usually much higher than kinetic. Who's pushed a piece of furniture really hard to get it going, but once it's going it's a piece of cake? Try it!
This is the same with a nail. The initial pull must be very hard, but once it's moving, it keeps coming out very easy.
Joe
I don't mean to be nasty (really, I don't), but who cares?
Maybe you can help us out here by explaining your premise -- or at least give us more explanation of the point you have in mind.
********************************************************
"I tend to live in the past because most of my life is there."
-- Herb Caen (1916-1997)
Nikki. He posted the same thing over in breaktime, and has had 100 responses posted, so I guess there are quite a lot if driving nails is your business.
From his posting on BT, I gather he's a "stage crew" veteran. These guys make a living building temporary structures with screws and foam (see the TLC show "Monster House" for more examples).
I don't care, either. I rarely use nails in woodworking. For structual building, various agencies have published shear and withdraw strength values for various nails sizes, based on size of the nail, penetration, and wood species. If I use these tables, the liability isn't mine if something goes wrong, which is the way I want it. The building inspector will also be alot easier to keep happy. There was a FHB article on this topic years ago, called "The Engineered Nail"; very interesting reading.
Now if I was planning to submit an engineering study to the approval agencies to get them to change or augment their model codes, then I'd care. But short of this, I don't see the point.
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