Home Depot 1/4" Lag Screw

[Leon]

Should have been using a grade 8 bolt.

[Existential Angst]

I measured a 1/4", just one, and its root measured .186-.187 top to bottom. I don't imagine lags are a precision item, tho.

And one of the links someone posted gives the pilot as 3/16 in softwood,

7/32 in hard! It also mentioned grease or vegeteable oil as a lube, but cautioned against soap. 1/4 lags are fragile, tho. I'd use 5/16 on anything semi-substantial.

[Chris Friesen]

For optimum strength in solid wood you actually want to drill the pilot hole smaller than the root diameter. Specifically between 0.7 and 0.9 times the root diameter, depending on the density of the wood in question--softwood gets a smaller hole.

Chris

[Tom Watson]

Where does that come from?

Regards,

Tom Watson

[JoeSpareBedroom]

I was referring to cute word wreckage based on language used by characters in cartoon strips.

[Lew Hodgett]

SFWIW, I use 75% of fastener size for the pilot hole size rounded to nearest standard size drill which can be either fractional, letter, or number size.

YMMV

Lew

[dpb]

...

Long lore, at least...

I don't have a direct URL; I'd expect you'd find the information in some of the US Forest Products Laboratory technical publications. It was something I was taught way back in one of first HS ag-ed classes is first I recall it personally, anyway...don't recall if it was taught as a specific ratio, only "tubafores get smaller, rr-ties get bigger" was the gist of it. :)

--

[Existential Angst]

Sheeit, I'll take word wreckage any day, over this goddamm valley-speak that's creeping into even mainstream advertising. That, and effing rap-speak... yo.

[Tom Watson]

I don't see the point. The pilot hole sizes quoted work for nails where compression determines strength but I don't see any benefit in having a pilot hole of less than the root diameter of a threaded fastener.

Regards,

Tom Watson

[dpb]

If they're a subsidiary of Grainger now, that's a newer realignment--they initially were bought by some (relatively) small Michigan(?) outfit that promised they were going to leave them essentially alone. I recall the letter from McNeely explaining how nothing was going to change. That was when the mail catalog was still only about 10-12 pages or so; almost all the square head and other wood fasteners w/ only a few other things thrown in...

OK, I went anna' looked -- Safety Supply, Inc is the holder which is in turn held by Grainger. But, they didn't buy McFeely until 2007 their site says. I surely thought that announcement was quite some time earlier than that. Came back to farm about this time in '00 and it seemed to me it wasn't much after that....ah, well, it's amazing how time all runs together as one gets geezery....

The original Mr McFeely was at another industrial supply outfit in Lynchburg that was a full-line Delta distributor amongst a zillion other things while we were there and left to start McFeely's about the time I left VA for TN. They started out as primarily a custom sawyer and millworks until after Bill was killed in mid-80s(?) in a mill accident...

[Doug Miller]

Torque to yield, on a head bolt???? Not something I've ever seen... OTOH, I drive old cars; the newest one I've ever had an engine apart on is my 85 Dodge pickup, about four years ago. Is that something [relatively] new?

[notbob]

Not necessarily. I had a similar problem, likewise, an alternator on a van engine. In my case, the entire top of the alternator hung off the extended bolt shaft. I changed to a grade 8 bolt and it snapped right off from vibration within a couple days, the grade 8 being too brittle. Went back to a grade 5.

nb

[Leon]

Yeah I remember that now, going way back. IIRC McFeeley himself sold the business to JIM? IIRC Jim? worked there already. The Grainger thing is pretty recent, last 2 or 3 years. The other one you are talking about was probably 20+ years ago.

[Leon]

I did not look and don't doubt your findings but if fully embedded threads are not going to hold, a tight hole is not going to be any better. IMHO making the pilot hole smaller will crush the wood fibers when the screw goes in and in turn would weaken the part that the threads cut into. Then add to that the unnessary extra torque to properly seat the screw which IMHO would increase the chance of breakage.

[Jon Danniken]

Cool, thanks Chris, that'll save me having to look up charts and deciding which one is the correct value next time!

Jon

[Jon Danniken]

Hmmm, not so sure about that. We have a fastener store her in town (where I picked up some *real* lag bolts today) that pretty much only sells US made stuff. I know for certain every box of fasteners in their warehouse is US made, and at the rate they continue to go through stock on a daily basis, it's current production stuff.

I think your supplier might be passing off incorrect information.

Jon

[Jon Danniken]

Bah, it was I who needed more coffee. What I meant to say was that 1/8" is actually too *large* for a 1/4" (size 14) screw.

Of course, that is for a wood screw, which I do realize now uses a slightly smaller hole than does a lag screw.

Jon

[Jon Danniken]

'Ya know, I sheared off a 1/4" machine bolt I bought from HD a half a dozen years ago. Same deal, was tightening it up, just past snug, when it turned to butter.

I figured it was a fluke, but maybe this last go round will be enough to convince me to steer clear of the bright shiny objects in the grabit bins.

Jon

[Jim Elbrecht]

-snip-

If memory serves my 84 Reliant had TTY. might have been that 86 Escort with the Mitsubishi engine-- but they are the newest cars I've had the heads off of.

Here's a bit about them- but no models mentioned;

Jim

[Existential Angst]

Well, it seems to me that compression would strengthen the material surrounding the lag threads. Think roll tapping (or thread forming) vs cut tapping, and/or think of a simple nail that compresses wood fibers. Roll tapping sposedly forms a stronger thread than cut tapping -- not perfectly analogous here, but it does sort of illustrate the benefit and strength of displaced material.

The Q is: what is the best overall compromise? In soft wood, I would go .010 smaller than root diameter, just to guarantee full thread engagement, esp. with iffy drilling. Which would only be .005 worth of compression. But, appaently in hard wood, you don't even want full engagement! Go figger....

The japanese dispensed with threads altogether, and just used dowels/pins/pegs. In the case, say, of a corner fence post, if you put snug-ish dowels in X, Y, and Z (per joint), the joint would be fully constrained. If all dowel holes were made through holes, the dowels could be easily removed. Actually, I think you could just as well dispense with the Z dowel, as each dowel effectively constrains 2 dimensions.

Don't know how practical this is, but it does have its own elegance. I heard recently about japanese/tibetan structures fastened like this, still standing after centuries -- nary a thread in sight. Of course, gravity helps in these cases, as well.