Screw length

[Donn]

I'm building a cage to protect potted plants and seed flats from squirrels. I'm using PT 4x4 uprights and 2x4 horizontals.

I have lots of 8x2 1/2" ceramic coated galvanized deck screws on hand. Are they long enough to attach 2x4's to 4x4's, or should I buy longer screws?

[paladin]

I seem to recomember my grandpappy telling me that a screw should be 2 1/2 times as long as the thickness of the material that I am trying to hold in place......so the threads in the support should be 1 1/2 times the thickness of the member being held, unless its white oak or Bois d'Arch and the damn screw izz gonna break off anyway...unless you pre drill....I imagine it's so with numerous other woods.

[JimConlin]

The 2x4's are 1-1/2" thick, so the penetration of the 2-1/2" screw into the 4x4's will only be an inch. Particularly since the points of deck screws are pretty fine, I'd like more penetration.

If you're desperate to avoid the trip to the store, you might countersink the screws 1/2" or so, yielding 1-1/2" of penetration which might be OK.

[Bruce Hooke]

It seems to me that a key point is that 2x4's are probably WAY overkill for the job at hand (unless the span between posts is very long).

So, yes, to actually realize anything close to the full strength of the 2x4's you would need longer screws (or more likely lag screws or bolts), but given what you are doing I'd give the screws a try and see if things feel solid once you've run in a few screws. You can usually drive drywall type screws a bit below the wood to gain some extra penetration.

The key issue may be that it can be hard to suck one board up against another if there are still threads left in the top board when the screw is fully driven. So, ideally you want screws where the unthreaded portion goes all the way through the top piece of wood. Otherwise you sometimes have to resort to pilot holes or clamps to get a tight joint.

[Donn]

It probably is overkill, but there's a lot of weight in a few hundred potted plants and seed flats. Initially, the unit will be 16' long, and I planned to use 5 pairs of uprights, a simple frame, 4' deep and 5' tall. Shelves will be equally simple, with 2x4 frame clad with 1/2" galvy hardware fabric. The exterior will be covered with 1" galvy chicken wire.

I thought about adding PL Premium to each junction, but decided I may want to take it apart someday.

I though about cutting notches (there's probably a carpentry term for that) in the 4x4's to inset the 2x4's but that seems like a lot of extra work.

I have to hit the store for the other materials anyway, so I might as well get some 10x3 1/2 screws and do it right.

[Nick C]

You can make those screws go deeper if you counter sink them a half inch or so.

[paladin]

yup...the idea is to leave the shank in the first piece and all the threads in the other....

[Dougster]

I think I'd go with the lag bolts/screws like Bruce mentioned. I used them on a chicken coop with the same size lumber and could winch 'em down good and tight with a socket set.

But I'm no carpenter Dougster

[brad9798]

you really could not figure that sh*t out, Donn?

Don't waste forum time for a bullsh*t question ...

[geeman]

I once dropped my boat off to have a newer motor installed.The "professional" shop that did the install actually screwed the controler to the boat using screws that went ALL THE WAY THE HULL.

[Bruce Hooke]

It probably is overkill, but there's a lot of weight in a few hundred potted plants and seed flats.

You're darn right there is. I was imagining some sort of fence or cage-like structure whereas it sounds like this is more of a table, at least in part. I would definitely use longer screws and I might even consider lag screws depending on how much weight we are talking about and how rigid the whole thing needs to be. A few 1x4 diagonals are also a good way of making the whole thing more rigid. You could still probably get away with 1x4 horizontals, but 2x4's should be fine too and are probably cheaper.

[Donn]

you really could not figure that sh*t out, Donn?

Don't waste forum time for a bullsh*t question ...

Please consider this, and all other questions I post, directed at serious members, and not at you, Brad. Your opinion on anything important, is of no interest to me.

10-4?

[Peter Malcolm Jardine]

I'm with Chuck, that there was some old rule as to a multiplication. I have always used the rule of the thickness of the piece I am attaching, and then half the thickness of the piece the screw is going into... but in your case Donn, I think 3 inch is the right size....(of course it has to be a different length than what you have on hand:D)

[Bruce Hooke]

FWIW -- According to the Wood Engineering and Construction Handbook, the penetration of the screw into the main member (i.e., the 4x4 in this case) should be at least 7 times the diameter of the screw to avoid having to apply a reduction factor for side loads. The diameter is calculated based on the expect load, and I'm fairly sure all of this assumes you are using traditional wood screws rather than deck screws. (How's that for some useless information? :D )

From a practical perspective, I ideally aim for a screw that is 2 1/2 to 3 times longer than the thickness of the piece of wood being attached, so the threads are mostly or all in the piece the screw is going into. However, quite often this is not possible because it requires that main member by a lot larger than the piece being attached. In this case the 3x rule would mean 4 1/2" screws, but realistically, since we are talking about deck screws that makes little sense. Something else is going to fail long before 3" of screw pulls out of the 4X4, so I'd probably go with 3 1/2" or 4" screws. Timberlok screws would be a great intermediate solution between deck screws and lag screws, but they are kind of expensive and probably not necessary in this case. Since the are put in with a hex driver they are easier to drive without caming out.

[Donn]

I got some 9x3 1/2's, as they were the only thing HD had other than lag screws.

Thanks for mentioning Timberlok, Bruce. I looked them up, and they sound terrific, but HD only had them in 6" and longer. I'll find some 4" somewhere.

[brad9798]

DEFINITELY 4" ... c'mon, Donn, with all your worldly knowledge you seriously could not figure out that ... without trolling some ridiculous question?

Get over yourself ... all it takes is a tape (measure) and some common sense.

[Donn]

You have a difficult time taking a hint, don't you Brad?

What is it about "Your opinion on anything important, is of no interest to me." don't you understand?

[JimD]

8 guage by 3.5 inches is what I almost always use for 2x4 construction.

[paladin]

I sorta figgered Donn wuz a bright enough guy to know that he would counterbore for the shanks and a start for the point into the mother wood......and it wouldn't hurt to have a bit of the shank in the 4 x 4 post.......when I bought this place it had a new deck installed using 2 x 4's and 4 x 4 verticals etc...all assembled with dinky little galvanized screws.....after we agreed on the price I said I'll pay the price in full when you bring the deck up to code.....the old boy figured he could do it for a couple of hundred bucks. A deck collapsed last year, three floors up, with a dozen partying school kids on it.....and the crap hit the fan on substandard decks. It cost him 8 grand to rebuild it.

[brad9798]

You are smart enough to figure it out DONN ... you bitch about others being to lazy to figure out things ... yet you are doing it by wasting bandwidth here ...

If you could not figure out screw length ... well, you know! :rolleyes:

blah, blah, blah ...