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paulz
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# Posted: 17 Jun 2020 20:52 - Edited by: paulz
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Just finished some shelving with 2x4 frame. I've taken to screwing most things together anymore, makes the mistakes easier to correct. For joist hangers etc. I've been using the Simpson screws with the hex head. Really nice, strong and don't slip out. Plus the long ones have a smooth shank long enough to go through a 2x and pull it tight to the board behind.
For countersunk I use deck screws. The problem I have is even with 3 1/2" length the smooth shank doesn't make it all the way through a 2x before it stars to countersink, so to get it to pull the board behind tight I have to bury the head way down, and even then it often fails to draw the back board in.
I've looked though all the types at my local hardware store, am I missing something?
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ICC
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# Posted: 17 Jun 2020 23:13 - Edited by: ICC
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There are two methods to use a screw to draw two members together to form a tight fit. To make it clear let's first define the names for the components being assembled. Engineers will refer to the side member and the main member. If we are fastening a sheet of plywood, a board or a metal bracket to a framing member like a stud or a joist, the plywood, board or metal bracket is the side member. The main member is then the stud or joist.
The screw threads must not engage the side member. That is achieved by (1) using a screw with sufficient shank length that is clear of thread under the head OR (2) by drilling a clearance hole in the side member, so the screw threads will not engage the side member.
****If fastening a deck board to a wood joist we should note that deck boards are not really meant to be 2x material like 2x4's or 2x6's. A proper deck board would be what is known as 5/4 thickness which is actually 1" true thickness. Have a look at what the lumber yards sell as deck boards. The common deck screws in 2-1/2" or 3" length usually have a 1 to 1-1/4" clear shank right under the head. When screwing down a 2x as you have found it is often necessary to overdrive the screw in order to snug it down tight. That looks ugly and actually reduces strength. Sometimes you can back the screw out a bit after it has engaged the main member, press the side member down firmly and then continue driving the screw.
For some uses like installing wood decking on metal frame utility trailers, there are special screws with ears or wings near the tip that ream a clearance sized hole through the wood. When those wings strike the metal framing they snap off and the self-tapping threads cut into the metal. The wood deck is then drawn tight to the metal frame.
If we were building furniture we would be drilling pilot holes and shank clearance holes to ensure the screws would be able to draw the side member tight to the main member.
Simpson Strong-Tie screws are made with sufficient non-threaded length under the head for the purposes where they are meant to be used.
Just FYI, a deck screw should never be used in an application to resist shear forces, such as fastening a wood cleat or metal bracket to a wall and using that to support a shelf. Deck screws are designed to be used to resist pullout. Screws like the Simpson range of screws are designed to resist both shear loads and pullout. There are others too.
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jhp
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# Posted: 18 Jun 2020 09:12
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I really like SPAX fasteners, myself. Never have to predrill in any size and you get 500#+ shear strength in #9 and larger size.
They're still available in bulk and don't cost an arm and a leg. I get them at Home Depot.
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ICC
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# Posted: 18 Jun 2020 10:26
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Those look to have a good length of unthreaded shank. I like the drive head too.
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paulz
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# Posted: 18 Jun 2020 10:32 - Edited by: paulz
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Those look good JHP, will investigate. The ones I'm using aren't specifically deck screws, I think they are advertised as construction screws or something, I forget the brand, got them at Ace. They have some knurling on the shank for countersinking, gold colored.
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