Stevan Cooper

lag / bolt table legs to frame

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I am making a heavy-duty farm table.  The top will consist of 2x8, 2x10, and 2x12's.  The frame underneath consists of 4x4's along the long sides with 2x4's across each end and several 2x4's spanning across.  I have made my own 5x5 legs (actually 5" x 5").  My question is how to best attach the frame to the legs.

I made several sketches (see attached) showing different views of how the frame will sit on the leg.  I showed each side, and then I showed separation between the fame and leg.  One view shows the leg off to the side, and the other shows the leg underneath.  I tried coloring some of them but  i think it just make it more confusing.  I hope it is clear enough.

The 4x4 frame will essentially rest on the 4x4 part of the leg.  a longer 2x4 part of the leg will extend up so that is can be attached to the side of the 4x4 frame.    I was just going to lag screw them together, which I'm sure will hold fine.  I only showed one screw on the side and one screw going down, but I will probably have room for two each.  I'm thinking 5/16" lags. 

I will hopefully never be taking this table apart once complete, but I am trying to make it as professional as possible.  I have never made much of anything other than some heavy duty shelves in my utility room.  It strikes me that unscrewing and re-screwing lag screws will wear away at the wood.  Again, hopefully i won't ever be unscrewing it, but who knows.  Bolts seem better for this purpose, but I don't want any through-bolts to be visible.  I know they make "lag threads" that I can sink down into the wood which will accept a bolt.  My only experience with them has been on a coat tree, and I have found them to break loose there.  How reliable are they?  Are they a good idea?   Any recommendations on the best way to attach?     

table.jpg

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Lags should work fine, with some caveats. First, the joint shown offers almost zero resistance to "racking", that is force applied horizontally against the table top. Unless you add some diagonal bracing, the legs will snap off quite easily.

Secondly, your wording leads me to assume this is a construction lumber project. Be aware that such lumber is NOT dried to the same standards as hardwood, and will be subject to shrinking. This alone is likely to make the joints (and even the lags) become loose as moisture leaves the wood.

I would add diagonal bracing to the corners, at a minimum.

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That joint will be very weak, in that it will allow the legs to rack easily. The lag bolt will act as a hinge pin & a soon as someone leans against the table it will pivot. Where the leg meets the apron, the wood will gradually compress, leading to more movement. When I say gradually, I mean probably before the first family dinner has been finished. Using 2 bolts with be better, keeping the leg sturdy for maybe half a dozen family meals.

Use the method @BillyJack shows above. It's a simple, easy to do joint and when the 1 leg nut is tightened, it pulls the aprons & legs tightly together and is surprisingly strong. The nuts may need to be tightened periodically though. Because the hanger bolt goes in the leg diagonally there's lots of length for a strong anchor point. The brackets are readily available & cheap. Repeated assembly & disassembly will not affect it.

Now a word about using construction lumber. Your best bet is to go to a real lumber yard where they carry a better selection of quality lumber than the typical home center. Get the best 2 x 12's you can, take them home & let them sit in you shop for a couple of months at least. Buy more than you think you'll need, maybe 25% - 50% more, because there will be a lot that will warp so badly they'll be unusable. After things are nice & dry, rip the pith out of the the 2 x 12's & then glue them up into the widths you need to build the table. Then at least you'll have something the will still be the same shape 6 months down the road. 

For finishing, I strongly urge you not to use a stain because it will be nearly impossible the get a good result. Construction lumber takes stain very unevenly & will look all blotchy. If you must stain, then spray it on. Paint would be a great choice for this type of project.

Good luck with your table.

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Thank you for all the good advice but yikes! I guess I'm going to learn the hard way with this project. I'm way too far into it to stop now. I did just use regular  lumber from Home Depot.  I have all pieces pretty much made  and I'm trying to do final assembly . This is my real first major woodworking project. So I may be experiencing the shrinkage that you're talking about. My wife does want an old beat-up weathered look so I do plan to put a bunch of Nicks and gouges all over the table before staining. But I don't think I'm going to like the idea of things warping. But like I said I'm way too far into it now.

 

Regarding the leg attachment, I don't know how I would do the diagonal corner joints at this point with the legs I have constructed. Just in case I wasn't clear I am planning to lag them both down and into the sides of the legs which I thought would prevent the racking that you caution about. Couple more photos attached here.

20200430_101017.jpg

20200430_100950.jpg

20200430_101347.jpg

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Wow lots of pocket screws! They work well, not a critique just an observation.

It wouldn't be difficult to put diagonal braces on the legs and stretchers. Line something up at 45 degrees and make a lap joint for the diagonal. It'll fit flush and give you excellent support. Longer bracing is stronger, to a point, unless you need clearance for storage underneath the table.

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3 hours ago, Martin-IT said:

@BillyJack the two crosspieces are just glued with the cornered block to prevent racking ? I do not see any screw hole.

There there to support the top,  but not fastened to the top.sometimes we will dodo these I  but in this case the drawings did not require these but I refused to make it without cross members so I added them after the fact....they are assembled with Dominos

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Okay, since you're this far along, let's turn this into a rescue operation. In addition to the lag bolt(s) through the leg tenon into the apron, add a couple of 12" RSS screws, driven vertically through the top of the 4x4 apron into the leg. Screwing into end grain like that is far from optimal, but with 8" of screw it should hold alright.

Now, about the top. You have glued and screwed the breadboard ends in a cross grain fashion to the table top. That WILL be a problem. As the wood looses moisture, it shrinks across the grain but there is almost no shrinkage along the grain. So when that table top tries to shrink as the lumber dries, the breadboard ends are going to try to stop it from shrinking. The result will be that the table top will split in one or more places. Nothing you can do to stop it. It will happen. But again, we can rescue this. 

Take out all the screws holding the ends on & cut both ends off. Reattach them using pocket screws & glue, but only for about 6" in the center. Use splines, biscuits or loose tenons along the rest of the joint to keep the ends aligned with the top. Now the top is free to move without splitting the top or tearing apart the joint. This means that the breadboard ends will not always be flush with the edges of the top, depending on seasonal humidity. I would rip just a hair off the top so the breadboards are just a little proud. If done perfectly, the edges will be flush during high humidity & the breadboards proud during low humidity.

When you secure the top to the base, be sure to use a method that will allow the top to move.

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@Stevan Cooper, I'm making an assumption that you may not possess all the tools typically used to accomplish the operations @drzaius suggested, but if you run into trouble, just ask. Some one here has very likely experienced the same situation at some point, and we can walk you through the steps of each task, using the tools you have at hand. I recently watched @James Wright make a seating bench from a fallen tree, and the only man-made tool involved was a half-inch chisel. If that was possible, your project is a piece of cake.

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Regarding the bread board ends:  couldn't he just remove the 3 outer on each end of the bread board end, drill them out (the part in the bread board end ) with a slightly larger bit and screw the screws back in?  This might allow for the movement.

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2 hours ago, Ronn W said:

Regarding the bread board ends:  couldn't he just remove the 3 outer on each end of the bread board end, drill them out (the part in the bread board end ) with a slightly larger bit and screw the screws back in?  This might allow for the movement.

The breadboard ends are glued as well as screwed. My guess is that the top would crack before the glue let go.

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Wow that's a good things to think about. I appreciate all the pointers.

So back to my lag srew questions. Seems like I might be okay as long as I screw down and screw into the side and I was thinking of adding some kind of diagonal brace.

I'm planning to use a drill bit a little smaller than the shaft of the lag screw to do my pilot holes. That way only the lag screw teeth will dig into the wood as opposed to trying to boring  its way through. That seems to be the best way from information I have seen. Agree?

Should I drill the same diameter hole for both pieces of wood, or should the lag screw pass freely through the top piece and only dig into the bottom piece?

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I would use a bit the same size or slightly larger than the shank of the lag screw. Driving them into a hole that is too small with split the wood. And the through-hole part should not engage the threads at all, otherwise the two pieces of wood will not draw together tightly.

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I had the same dilemma the other day as to which bit to use and googled drill bit size for such and such lag bolts and there several charts available. 

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