Dear Dr. Rev. Chuck, M.D. P.A.:
Worry about the plywood, not the bolts. Can you describe "hanging" a little more clearly? What is the orientation of the board, the support you are putting the bolts through, and the orientation of the "per 100 lbs load"?
Are we creating a gallows for Mr. Wittke (alias EinsteinHoax) or some more permanent structure?
David A. Smith
So you are hanging a board on a wall but the board is to be horizontal? So the wall is presumably horizontal too. That's a curious definition of the word "wall". Maybe "ceiling" or "floor" would be more appropriate?
Dave Baker - Puma Race Engines
Not sure how you arrive at that figure. If the bolt is the correct length, i.e. all the threaded portion is within the wall then the shear area would be the main body of the bolt with an area of 0.077in^2.
Dave Baker - Puma Race Engines
Hanging a 4 x 8 foot, 3/4" plywood tool board. What are the shear failure ratings for common 5/16 and 3/8" lag screws? IOW, how many bolts per each 100 lbs load would be needed to provide a worry-free
2 or 3x safety margin?
On a wall, with bolts driven through to wherever I can locate a stud.
Horizontal.
2 x 4 divider wall resting on a concrete slab, the slab resting on planet Earth.Evenly distributed over the whole panel. Or approximately so.
The gallows comes later. I'm still behind schedule a month on the electric chair.
The OP uses both terms in his enquiry so we are none the wiser.
Dave Baker - Puma Race Engines
-- 0.0524 in^2 is the tensile area, based on the mean on the pitch and minor diameters.
True. I assumed worst case conditions for everything else anyway.
For a 5/16" lag, assume 1/4" diameter section for the threaded portion.
That's be a celing or floor.
The screws are loaded in tenion not shear then. So you need to the tensile strength of the screw, not the shear strength.
Please discontinue the sexual innuendo.
He's making a loft and he's fantasizing about sharing it with a hot babe. Let's see, 350 pounds max (unless he has a fat fetish) + force of thrustration (frustration relief with a 200 pound max load is more likely) ....
5/16 bolts with washers will work fine.
Lots of imagination for a troll.
Which of us has more patents?
I think a screw is defined as being held by threading into a material, while a bolt is defined as being held by a nut (ref Shigley, among others) . I.e., look at it as a definition of application of a threaded headed device, rather than the name of the device itself, e.g., a 1/4-20 2" hex head can be used either as a bolt or a screw.
Flat head wood screws, for example, all have unthreaded shanks.
Yea probably not a general definition really.
I can't find anything in Shigley's ME Design book that agrees with that. It may be buried somewhere. The book uses the terms screw and bolt almost interchangeably.
A power/lead screw is fully threaded and is referred to as a screw not bolt. Aerospace fastener specs (NAS, MS, ..) refer to fasteners with unthreaded shanks as bolts and fully threaded fasteners as screws.
Probably an exception. They would not be referred to as bolts since they have pointed tips.
This is what the trades use for a definition too.
In those cases, the unthreaded portion is to provide a bearing surface when joining two or more "boards".
Another exception is a carriage bolt, which is almost always threaded all the way up, and is always called a carriage bolt.
All rules have exceptions, probably even this one! ;>}
David A. Smith
I did not find my Shigley (not on the library shelf - likely buried in a pile somewhere) - I am pretty sure it is in there, near the section on markings
However, I did find some information 1) that indicates the threaded shank is not the criterion, 2) a reference to a source that may further define them, and 3) some background information about screws vs bolts for at least one kind of screw that looks a lot like a bolt.
First, in background, I have spec'd HH bolts and HH screws, and as a young engineer I was called to inspect them when the shop reported threads were "wrong" for bolts. Going back to the mfg, ANSI, and steel codes to check them out back then, I found that the thread length was not the criterion.
OK - 1) from the AISC handbook: they reference ANSI B18.2.1 and have a table (no table ref #, p 4-141) for minimum length of thread on bolts - roughly 2d +
1/4 for lengths under 6 inches. Thus, ANSI said bolts may be partly threaded or fully threaded, and the shorter lengths MUST be fully threaded (e.g. 3/4 " 1/4-20)2) ANSI B18.2.1
And, 3) from an old Vincent (supplier) engineering handbook - not much comment in the bolt section, but in the screw section:
"...HH cap screws can usually be substituted for HH bolts, [but] HH bolts should never be substituted for HH cap screws for the following reasons:"
a. HH cap screws 'must' [italics] have a washer face under the head but the bolt may not [I understand that face is the round flat under the hex]
b. The shank diameter tolerance of a cap screw is much more limited than than that of a hex bolt. (3/4 inch in their example has the tolerance range cited on screws as .009, and onbolts as .115)
c. cap screws 'must' [again italics] be header pointed, but hex bolts need not.
d. they note that both cap screws and hex bolts of the same size have threads of the same length. -- and finish, etc.
hope it helps - the ANSI std may have a specific definition
An unlikely but helpful resource for this type of information is a small book published by Bowman Fasteners called "Fastener Facts". I'm quite sure they deal at length about shear strength. How the fastener is used also needs to be considered. A properly torqued through bolt with nut behaves differently than a bolt threaded into a hole. Industrial Fastener Institute's "Fastener Standards" also has a section on shear applications.
The bolt vs screw debate is primarily a personal preference thing in my opinion. You can find a definitive source to support almost position. When in doubt, I'm frequently inclined to defer to Machinery's Handbook, but in this case I'd use IFI's "Fastener Standards" for questions on definitions as they have taken the lead in this area. I'll bet that Machinery's Handbook will agree with IFI as Machinery's Handbook is just a compilation of data from other sources.
Jon Juhlin
The previous poster is correct. A screw is designed to be turned into something, whether it be a threaded hole, a piece of sheet metal or a piece of plywood. A bolt is designed *not to turn* but to have a nut (and generally a lubricated nut) turned onto it. There is a difference in the ultimate sheer and tensile strengths of equally sized screws and bolts. Bolts are generally less able to withstand torsional loads since they are primarily intended to withstand the tensile load applied by the (lubricated) nut. While it's not always easy to tell the difference, many bolts do not have the radius at the interface of the shank and head that most screws have.
That's misleading because, while many bolts *do* have an unthreaded shank, the fact of an unthreaded shank does not make it a bolt. The reason for the unthreaded shank is because the bolt is intended to go into a clear hole and have the nut apply the holding load from the other side so there is no need for threads, where as a screw is intended to draw down against it's own head and if there were an unthreaded shank it couldn't be tightened up against the piece it is intended to hold (unless there were washers or some such).
No, they are screws because they are intended to tighten up against their own heads. The unthreaded shank on a wood screw is intended to take the place of a lock washer, the tight interference fit preventing it from backing out.
Not really...see above.
Not correct, "carriage" bolts aren't threaded all the way up, they all have a square shank which prevents the bolt from turning as the nut is tightened...
From Machinery's Handbook, 21st Edition, page 1131: "A bolt is an externally threaded fastener designed for insertion through holes in assembled parts and is normally intended to be tightened or released by torquing a nut. A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating with a performed internal thread or of forming it's own thread and of being tightened or released by torquing the head." They go on to give a series of examples such as round head, track head and plow "bolts" and wood and self taping "screws" etc...
...Ken
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