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Need Help with Pocket Hole Joints in 2x4

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Forum topic by pcox posted 05-07-2016 12:41 AM 1181 views 0 times favorited 19 replies Add to Favorites Watch
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pcox

25 posts in 229 days


05-07-2016 12:41 AM

Hello,
I am a beginning woodworker and am starting my first project. I am building a salt water mixing stand out of 2×4s and plywood. The structure will be 2×4s and the shelves will be plywood.

I have cut my 2×4s and drilled all of the pocket holes. I then primed and painted. Now today I started joining the pieces and am having the following problems…

1. First, I am having a hard time telling when the screw is in far enough into the pocket hole. My drill has a clutch on it but I don’t really know where to set it.

2. Then my joints don’t really seem that strong. The picture below shows how I am joining the 2×4s. I am using 2 pocket holes at each joint. I filled 1 1/1” holes and I am using 2 1/2” Kreg screws.

3. And since the joints didn’t seem that strong, I tried driving the screws a bit deeper and ended up drilling through the other side.

So any suggestions would be appreciated. Thanks!


19 replies so far

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CharlesA

3022 posts in 1262 days


#1 posted 05-07-2016 01:15 AM

From the pics and my experience, I would think the pictur of the joint in the front picture should be plenty string if done correctly, but the picture of the joint in the side picture is pretty rickety with support on only one end. A stretcher would help.

-- "Man is the only animal which devours his own, for I can apply no milder term to the general prey of the rich on the poor." ~Thomas Jefferson

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pcox

25 posts in 229 days


#2 posted 05-07-2016 03:20 AM



From the pics and my experience, I would think the pictur of the joint in the front picture should be plenty string if done correctly, but the picture of the joint in the side picture is pretty rickety with support on only one end. A stretcher would help.

- CharlesA

Thanks for your reply. I was planning to add stretchers but even without them, I didn’t think the joint should move at all but it does. It does not take much force to make the leg wobble with two pocket screws. Are two screws enough for joining 2×4s? Am I using the correct size screws? I have seen videos on the strength of pocket screws and I expected them to be much stronger joints than I am getting so I feel like I am doing something wrong.

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devann

2201 posts in 2157 days


#3 posted 05-07-2016 05:27 AM

1. To know when to let off the trigger when joining with pocket screws I watch the joint. When it butts up tight you’re done. Tip: Get your self a impact compatible with your drill/driver. Most manufacturers offer one. They generally produce 3x the torque of the drill driver made by the same manufacturer. You will strip out less screw heads and gain a new level of control and “feel”.

2. Different species of wood will yield a different feeling of joint strength. A pocket hole joint made with Spruce Pine Fir (softwood) will not feel has strong as one made with Ipe (hardwood). Most of the weakness felt in your joints is because of the design shown in your drawings. I realize you said you were going to add stretchers to the lower portions of the legs, that will help a lot.

3. Check your drilling jig thickness settings. Remember, the pocket hole jig is setup so the screw exits the center of the board the screw is placed in. You might back it off a little, set it for a thinner board to give yourself more room screwing into the board that you’re joining.

And, don’t forget to use glue when making pocket hole joints.

Another pointer for future framing designs. Wood used horizontally should be supported by wood used vertically. Do not rely on mechanical fasteners where weight is to be supported. Joist hangers are about the only time you can get away with using mechanical fasteners to support weight. In that scenario you should be using structural grade nails or screws only.

Here’s how that applies to your drawing;

Front/back: Cut the top board 21” long, making the top edge of the board 18” long, centered. This will allow the board to rest on top of each leg. Drill a pocket hole at the end to join the 24” side board. Cut the lower stretcher 18” long. Place where at a desired shelf location. I would use a set of pocket holes at each end to join to legs.

Sides: Cut the top board 24” long, making the bottom edge 21” long, centered. This will allow you to have both the front and sides supported by the legs and still allow for using two pocket hole locations at the legs. Cut the lower side stretchers at 21” long simply butting the 18” front/rear stretcher, place one screw through the front/rear stretcher into the side and then two screws through the side stretcher into the leg. Glue and screw plywood to the top of the stretchers forming a lower shelf inside of the legs.

Using the stretcher lengths I described you could not put a lot of weight on the lower shelf because it is merely supported by screws. If you needed a shelf for heavy items you could notch the legs and then lengthen the front/rear stretcher accordingly.

-- Darrell, making more sawdust than I know what to do with

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Rick M

7921 posts in 1844 days


#4 posted 05-07-2016 07:02 AM

The problem is you are not using proper table design. With the top connected to the legs there is nothing to prevent racking. Tables have aprons or stretchers and it’s actually the shoulders on those that make a table rigid. Pocket screws will be fine and plenty strong. I built a lathe stand with them and it was very strong and completely rigid. Just modify your design similar to below and you’ll be fine.

And for how far, the screw head bottom just need to bottom out in the pocket and you’re good.

-- http://thewoodknack.blogspot.com/

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pcox

25 posts in 229 days


#5 posted 05-07-2016 01:57 PM


1. To know when to let off the trigger when joining with pocket screws I watch the joint. When it butts up tight you re done. Tip: Get your self a impact compatible with your drill/driver. Most manufacturers offer one. They generally produce 3x the torque of the drill driver made by the same manufacturer. You will strip out less screw heads and gain a new level of control and “feel”.

2. Different species of wood will yield a different feeling of joint strength. A pocket hole joint made with Spruce Pine Fir (softwood) will not feel has strong as one made with Ipe (hardwood). Most of the weakness felt in your joints is because of the design shown in your drawings. I realize you said you were going to add stretchers to the lower portions of the legs, that will help a lot.

3. Check your drilling jig thickness settings. Remember, the pocket hole jig is setup so the screw exits the center of the board the screw is placed in. You might back it off a little, set it for a thinner board to give yourself more room screwing into the board that you re joining.

And, don t forget to use glue when making pocket hole joints.

Another pointer for future framing designs. Wood used horizontally should be supported by wood used vertically. Do not rely on mechanical fasteners where weight is to be supported. Joist hangers are about the only time you can get away with using mechanical fasteners to support weight. In that scenario you should be using structural grade nails or screws only.

Here s how that applies to your drawing;

Front/back: Cut the top board 21” long, making the top edge of the board 18” long, centered. This will allow the board to rest on top of each leg. Drill a pocket hole at the end to join the 24” side board. Cut the lower stretcher 18” long. Place where at a desired shelf location. I would use a set of pocket holes at each end to join to legs.

Sides: Cut the top board 24” long, making the bottom edge 21” long, centered. This will allow you to have both the front and sides supported by the legs and still allow for using two pocket hole locations at the legs. Cut the lower side stretchers at 21” long simply butting the 18” front/rear stretcher, place one screw through the front/rear stretcher into the side and then two screws through the side stretcher into the leg. Glue and screw plywood to the top of the stretchers forming a lower shelf inside of the legs.

Using the stretcher lengths I described you could not put a lot of weight on the lower shelf because it is merely supported by screws. If you needed a shelf for heavy items you could notch the legs and then lengthen the front/rear stretcher accordingly.

- devann

Thanks for your reply! Just to give a bit more information on my project, I am building a stand that will hold two 16 gallon water containers that will be used for making saltwater for my aquarium. So you should think of this as garage type furniture. This is why I am just using plain 2×4s and b/c 3/4” plywood. Each container will weigh something like 140 pounds when full of water.

Ok, here are my comments to yours and some further questions…

1. I wonder if I am clamping the pieces together too tightly while I am installing the pocket screws? Could this keep the pieces from joining well?

Also, what size drill would you recommend for this task and for general woodworking? My plan after building this stand is to build some shop furniture / cabinetry out of 3/4” plywood, a bench for our front porch and then we will see from there. Most likely I will focus on plywood cabinetry and some small hardwood tables. Currently I have a Craftsman corded drill that I use for drilling the pocket holes and then I have a small Ryobi 12v cordless drill that I am using for installing the screws. I wonder if I need a larger cordless drill?

2. I suspect that the joint movement may be due to the fact I am using plain 2×4s, which I believe are cut from soft wood, correct? And please see drawing below. Is this better? Should I add anything to the back? Maybe a stretcher on the back?

I don’t really follow your comments regarding “top edge” / “bottom edge.” Please see the drawing below and let me know if you would make changes here. The way I was thinking about this was the the side rails will rest on the legs and provide the top down support. The front rails will simply join the left and right side structures and hold them together. and then the 3/4” plywood top would hold it all together as well. I would also add something to the back.

On the drawing, some of the measurements are very slightly off as I am new with sketchup.

Thanks again for your help!

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pcox

25 posts in 229 days


#6 posted 05-07-2016 02:10 PM



The problem is you are not using proper table design. With the top connected to the legs there is nothing to prevent racking. Tables have aprons or stretchers and it s actually the shoulders on those that make a table rigid. Pocket screws will be fine and plenty strong. I built a lathe stand with them and it was very strong and completely rigid. Just modify your design similar to below and you ll be fine.

And for how far, the screw head bottom just need to bottom out in the pocket and you re good.

- Rick M.

Thanks for your comments Rick! Please see the drawing I posted above. I don’t know the terminology but it look like I have added a stretcher down lower on the legs and your drawing shows it higher? Of is that a different component? Thanks for any further comments.

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Ger21

1047 posts in 2595 days


#7 posted 05-07-2016 02:15 PM

Your stand will likely collapse the first time you fill up the water tanks.

Butt joints with pocket screws using 2×4’s is a very weak joint. Add to that the fact that you have no lateral support, which will put a LOT of stress on those joints.

You’d be better off to get some 6” Deck screws and screw the joints together.

I’d also highly recommend gluing the joints together, and assembling prior to painting.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

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pcox

25 posts in 229 days


#8 posted 05-07-2016 03:14 PM



Your stand will likely collapse the first time you fill up the water tanks.

Butt joints with pocket screws using 2×4 s is a very weak joint. Add to that the fact that you have no lateral support, which will put a LOT of stress on those joints.

You d be better off to get some 6” Deck screws and screw the joints together.

I d also highly recommend gluing the joints together, and assembling prior to painting.

- Ger21

Thanks for your reply. What would you change about it structurally to still use pocket screws?

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devann

2201 posts in 2157 days


#9 posted 05-07-2016 04:25 PM

Rick (comment #4) is correct about a standard table design. However the legs a generally thicker (square) than the aprons allowing for the load to bear on top of the legs in both directions. Sometimes the load bearing is picked up with a mortise & tenon joint.

Pat, your table isn’t designed with this feature, your legs are the same thickness has the aprons in one direction. Generally, aprons are what the boards between the legs under the top are called, stretchers are the boards located lower on the legs usually forming lateral bracing for stiffness.

You mentioned that you have already cut and primed most all of the parts. My solution was based on work you have already done. You will need a little more wood.

When referring to the “top edge & bottom edge” I was talking about the boards pictured in you first drawing.
Your top is going to be 21”x24”. That is the size of your plywood top. Using 2-2×4s 21” & 2-2×4s 24”.
Cut 1 1/2”x 1 3/4” notches in both ends of all four boards. Place the notches up on the 21” boards and down on the 24” boards forming a rectangle with all edges flush. This will be you load bearing top. Assemble as you planned.

Next add table aprons. You can make these from the 3/4” plywood you’re using. Cut them 18”x 7” for front and back, and 19 1/2” for the sides. Place the plywood aprons inside of the table top frame flush with the top of the frame. Glue & screw. That should take care of any lateral movement of the table.

You can add a shelf below has I described earlier. It will also help the eliminate lateral movement. If the lower shelf needs to be load bearing add 2×4 blocks below the stretchers making the bottom portion of the legs 3”x 3 1/2”.

Pat, your comment #5

1. No, you’re not clamping too tightly. No, you don’t need a bigger drill. As mentioned an impact that uses the same battery as your drill/driver would be a wise investment. There is night & day difference in the control you’ll have when installing screws.

2. Lateral movement was because your aprons didn’t extend down below the top of the legs. A 7” wide apron I described will give you 3 1/2” below the top of the leg.

I hope that helps you out with you build.

-- Darrell, making more sawdust than I know what to do with

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Rick M

7921 posts in 1844 days


#10 posted 05-07-2016 05:40 PM



Thanks for your comments Rick! Please see the drawing I posted above.
- pcox

No offense but it will fall apart if you build it like that. You are trying to design a stand without understanding what makes them strong or rigid. Aprons and stretchers go between the legs to make them rigid. You can also use cross bracing but that’s amateurish in woodworking, fine for metal, not for woodworking.

Here is a revised sketch of your stand. This is a quicky, not to scale, just to show how the pieces should go together. This is side and front. Mortise and tenon would be stronger if this is to hold a lot of weight but if you stick with pocket screws, use them on each side of the stretcher so there are 2 on the outside, 2 on the inside, and use glue on the butt joints. I have to run but can add more info later.

-- http://thewoodknack.blogspot.com/

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Ger21

1047 posts in 2595 days


#11 posted 05-07-2016 05:59 PM

Something like this would be better.
Using 6” long screws instead of pocket screws would be even better.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

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pcox

25 posts in 229 days


#12 posted 05-07-2016 06:24 PM

Rick M. and Ger21, very helpful! Thanks so much! And yes, you are correct, I don’t know what I am doing….yet! I am going to start over since I only lose a couple of 2×4s. I’ll be back in touch.

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Rick M

7921 posts in 1844 days


#13 posted 05-07-2016 07:25 PM



Something like this would be better.
Using 6” long screws instead of pocket screws would be even better.
- Ger21

Is that two tables stacked?

Look folks, table/workbench design is fairly standard. I can design it five different ways (at least) but the one I posted is quick and easy. I could build this with pocket screws and it will not collapse. Whether someone else can, I don’t know, but pocket screws are pretty damn easy, just don’t over think it. People get too focused on whether pocket screws (or any other thing) is as strong as something else—most of the time it doesn’t matter. What matters is whether it is strong enough and that typically boils down to design. Screws are screws. Use good quality ones and use them properly and you’ll be fine. Glue helps too. A glued butt joint is still pretty strong. A bench/table like the one I posted is stronger as a unit than it’s individual pieces. If you’ve ever seen a semi trailer built, the walls and floors are floppy and weak but once it’s made into a box the whole becomes very strong. Tables are the same way. But if you don’t think pocket screws will hold then I would go to half laps.

-- http://thewoodknack.blogspot.com/

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pcox

25 posts in 229 days


#14 posted 05-09-2016 12:11 AM

Well, I made some good progress today. I was able to complete both tables. The lower table is perfectly square and the exact dimensions I was going for. The top table is slightly out of square but I think it will be OK. Also, both tables seem very sturdy. Thanks for the design help!

I did unfortunately install one of my sides on the top table the wrong way and my pocket screws to attach it to the lower table are on the inside, not outside so I will likely have to drill new pocket holes on the outside. I was also thinking I will need something additional to hold it all together. Should I maybe install a 1/2” or 1/4” plywood back or even partial back?

Thanks again for the help!

https://photos.smugmug.com/photos/i-VSSnp4w/0/XL/i-VSSnp4w-XL.jpg

https://photos.smugmug.com/photos/i-V6nd5nc/0/XL/i-V6nd5nc-XL.jpg

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CharlesA

3022 posts in 1262 days


#15 posted 05-09-2016 12:45 AM

Back when I used pocket holes a lot, I used the Kreg project plans as a guide to how to construct things well with pocket holes. I think you’ll find them really helpful in general.

-- "Man is the only animal which devours his own, for I can apply no milder term to the general prey of the rich on the poor." ~Thomas Jefferson

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