What length screw for joining 2 x 4's together? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 14 Old 04-16-2013, 02:06 AM Thread Starter
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What length screw for joining 2 x 4's together?

A 2x4 is 1-1/2 inches x 3-1/2 inches. If you're joining them face to face, that's 3 inches thick. A 3 inch long construction screw is ideal, but if you sink the screw head below the surface too far, the tip will blow out the other side. A 2-1/2 inch screw only goes into the 2nd 2x4 halfway, giving you only about an inch of material for the threads to bite. I've thought about going with 3 inch washer heads to keep from sinking them too far, but I thought I'd ask you guys what you thought first.
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post #2 of 14 Old 04-16-2013, 06:41 AM
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Quote:
Originally Posted by Merkava_4 View Post
A 2x4 is 1-1/2 inches x 3-1/2 inches. If you're joining them face to face, that's 3 inches thick. A 3 inch long construction screw is ideal, but if you sink the screw head below the surface too far, the tip will blow out the other side. A 2-1/2 inch screw only goes into the 2nd 2x4 halfway, giving you only about an inch of material for the threads to bite. I've thought about going with 3 inch washer heads to keep from sinking them too far, but I thought I'd ask you guys what you thought first.
What are you doing this for? I would use 2 1/2 and if for some reason I want it to bite more I would just countersink one of the 2 x 4's.

Last edited by mengtian; 04-16-2013 at 07:05 AM.
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post #3 of 14 Old 04-16-2013, 08:04 AM
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Run the 3" screws on a slight angle. Then it won't go through. You could also use a bit of glue with the 2 1/2" screws if you think they are insufficient.
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post #4 of 14 Old 04-16-2013, 08:15 AM
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Quote:
Originally Posted by Merkava_4 View Post
A 2x4 is 1-1/2 inches x 3-1/2 inches. If you're joining them face to face, that's 3 inches thick. A 3 inch long construction screw is ideal, but if you sink the screw head below the surface too far, the tip will blow out the other side. A 2-1/2 inch screw only goes into the 2nd 2x4 halfway, giving you only about an inch of material for the threads to bite. I've thought about going with 3 inch washer heads to keep from sinking them too far, but I thought I'd ask you guys what you thought first.
if you only have 2 1/2 screws run one from each side, that way you will have them joined real good
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post #5 of 14 Old 04-16-2013, 09:41 AM
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I'd go with 2 1/2" screws and not worry about it. The rule of thumb I always heard was that at least 1/3 of the fastener should be in each piece of wood, and it's worked for me so far.

If it's a sufficiently high risk situation that I'm worried about whether that will hold, I'd drill through and use a carriage bolt with locktite on the nut.
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post #6 of 14 Old 04-16-2013, 09:56 AM
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If all you have are 2Ĺ" screws, they should work. Or, get some 2ĺ" square drive screws like these.





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post #7 of 14 Old 04-16-2013, 11:16 AM
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If you are driving these with an impact driver, use 2-1/2" length and drive the heads down 1/4" inch or so. I've been amazed at the power of impact drivers ever since I got one a couple years ago.

I recently put a bigger front door in and had to re-frame the wall. I used all deck screws and no nails. Drove them all with an impact driver. Worked great!

Bill
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post #8 of 14 Old 04-16-2013, 12:07 PM
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I do really low-level building. Freight pallet tables for garden, greenhouse, log cleaning for wood carving and stone carving. They all have to be extremely "bash-worthy". In the past 5 years, everything made with 2x4's and 2 1/2" Robertson screws, mostly #12. Nothing has come apart, much to my satisfaction.

I agree with Del Schisler (#4), if you can drive screws in from both sides, you are done.
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post #9 of 14 Old 04-16-2013, 01:12 PM
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for face to face 2x material, i use 2 1/2" decking screws and glue. they go 1" into the 2nd board, and futher if i countersink them a little. there is no possible way that they are going to come apart.
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post #10 of 14 Old 04-16-2013, 06:05 PM Thread Starter
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Quote:
Originally Posted by mengtian View Post
What are you doing this for?
I was thinking about building this workbench here. She specifies using 1-1/2 inch and 3 inch screws.
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post #11 of 14 Old 04-16-2013, 09:48 PM
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i have used 2x3s either 2 or 3 thick, glued and screwed with decking screws for all of my workbenches. they are strong enough that you could put a car up on them.

this one is my last bench, a new-fangled style bench. it is so versatile that it will probably be the last bench i make.
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Last edited by Chris Curl; 04-16-2013 at 09:54 PM.
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post #12 of 14 Old 04-17-2013, 10:57 AM
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you could always do 2 1/2 from both directions if it's not already mounted.
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post #13 of 14 Old 04-17-2013, 01:02 PM
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I used 2 1/2 inch screws and glue when I built the legs for my bench. You should never have a problem. My bench is strong as the dickens and will stand up to all I can give it.

Note: I drilled pilot holes for the screws and rubbed them on a bar of Irish Spring soap before driving them home with an impact driver.

Here are a few pics I took during the build. My garage is so unlevel, I made my own table levelers from 5/8 inch bolts and nuts glued into the legs with Gorilla Glue.
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post #14 of 14 Old 04-17-2013, 02:25 PM
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I made a very similar bench from a plan and YouTube video by Mark Donovan. In fact, i think the dimensions are virtually the same. Easy to google. The advantage of his is that he uses half lap joints with 2x4's which are strong, easy and solve your screw length problem.

Last edited by Saxe Point; 04-17-2013 at 02:39 PM.
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