# Screw/lag bolt selection. Dining Table



## sbjmg (Aug 23, 2012)

I am building a dining table made of solid 8/4 Walnut. 73"x40".

For the legs I am building 2 squares out of 1/4"x4" flat steel. 26"wide x 28.5" high.

The question is when screwing/bolting the legs to the table what type of screw should I use, what size, and what length.

I was thinking 6 lag bolts spaced about 6 inches apart for each leg, each bolt would be staggered half inch from bottom to half inch from top since I have 4 inches to play with. For size I was debating between 1/4, 5/16 and 3/8ths. For length I am contemplating between 1", 1.25" and 1.5". Keep in mind the steel is .25 thick so with a 1" bolt I will only get .75" of wood. Assuming the table top is finished at around 1.75" since I am starting with 8/4.

Thanks

Below is a picture of something similar


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## Doss (Mar 14, 2012)

Depending on the grain orientation of the wood and environment, you're probably going to have to allow for some seasonal expansion.

You don't need to fasten the top like it's a wing to an airplane. It just need to stay attached.

If you're depending on the fasteners to keep the legs from tilting, you're probably going to have to get a little creative and have it solidly mounted in the center room for expansion on the edges.


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## sbjmg (Aug 23, 2012)

OK to clarify. The table will be made from 5 boards each 1.75" thick 7to11" wide and 73" long. I will go ahead and use 1/4" x 1-1/4" screws unless you feel otherwise.

I take it that it is a bad idea to screw the boards together via the top of the metal square as this will not allow for expansion? How would only screwing the two end pieces to the metal allow for expansion unless the top of my metal square is not present and is only a U shape with 2-3" bends on top to screw into just one plank. My main concern is wobble, I figure 4" wide steel flats would have taken care of that but if not what should I do?

In regards to the table top it will be made of solid walnut that I will oil with Danish oil and then finish with a wipe on Poly. It will be indoors in southern California temperatures will range from 60-90 at the extremes.

Thanks again.


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## Doss (Mar 14, 2012)

I'm having a little trouble visualizing what you're talking about (as it seems you're talking about several options).

If you screw in directly to the metal (table top to top metal cross bar), then I'd probably slot the metal screw holes to allow for movement.

If you remove the top piece of metal (ending up with a U shape), that would allow for some movement I would think, but I don't know how much resistance the wood would encounter (which may cause the wood to buckle at the seams).

That' just if I'm understanding your design correctly.

You're fine to bolt to the metal, you just have to allow for some expansion along the width of the table (not the length… if the grain is running parallel to the length which I'm assuming is the case).

The temperature is not so much of a concern on its own, it the humidity as well.


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## bondogaposis (Dec 18, 2011)

If the grain direction of the table runs the length of the table Then I would attach using 3 lag bolts on each leg. One in the center and one each on the sides. Slot the metal for the lag bolt holes on the outside of the legs so that the table can move in width w/ changes in humidity. 1/4" by 1/14" lags should be fine, I'd use flat washers too.


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## sbjmg (Aug 23, 2012)

I am sorry. I came here to get help from you professionals but instead forced my ideas in. Let me start over. The above picture is my goal. What would you guys do to get there.

Again I apologize for assuming methods when I have little to no idea what I am doing hence the reason I cam here.

In regards to slotting the metal, how does that work, since when I bolt/screw it down. I assume I am torquing it quite a bit, when the wood expands does it just force the bolt sideways or am I not supposed to crank down on the bolt, as this brings up the "wobble" question if I am not torquing it down.

Sorry for all the questions, I truly am a novice. I spent a lot of my money on this beautiful wood I just do not want to mess it up.

Thanks


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## Doss (Mar 14, 2012)

Okay, I'm going to try and help explain it a little more.

I have drawn these out so maybe it'll help a little more. Here's the explanation:

You're going to need to make a slot cut (approximately 2 1/4" holes side by side) in the metal to allow for wood movement. You're not going to torque down the table top so tightly that it can't move. You want to allow some movement so it just gets "snugged down" - (tight enough that you can't just move the top by hand but loose enough that you're not crushing the wood fibers). If you tighten it down too much, the screws will almost definitely become small drill instead and you'll end up removing wood that was being used by the screw to fasten.

So, here's the picture: 









EDIT: REDO









The part with the orange around it is a blow up of what I'm trying to explain.

Let me know if this helped or not.


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## sbjmg (Aug 23, 2012)

Doss, you are the man. I now know exactly what you are suggesting. What size screws/lag bolts would you use?

What about wobble? Since I am not torquing down what can I do to be "creative" and ensure no wobble or do you think the legs being 4" wide I should be ok?


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## Doss (Mar 14, 2012)

Well, I don't know too much about how stable that design will be. My suggestion would be to run the screws zig-zagged or on both sides (as much as possible) of the top of the boxes.

In the picture (the right part where I have one oval hole illustrated), I'd instead use two (one near "This allows for…" and the other by those faint words at the bottom ("Top of metal box") if you can understand that.

Like *Bondo* said, I think those 1/4" will be fine. If you run enough of them (maybe 4 per board per box in a three board top), that could work. Most people would probably put a stretcher across from one section of boxes to another, but that would possibly interfere with the design. You could weld on extension straps of 1/4-1/2" thickness extending from the tops of the legs down the length of the tabletop (maybe extending 1' from the boxes) and secure those with a few extra screws. This would probably go a long ways to keeping the table from swaying (even though it's a little hard with so many parallel and perpendicular supports).


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## sbjmg (Aug 23, 2012)

Ok Table top is almost done. I am about to have the legs done up as suggested by Doss above with slots cut out. I am thinking now for stability purposes to have the bottom and sides 1/4" x 4 but the top pieces to be 6" or 8" wide to give me a more ridgid table/remove possible sway.

My last question is in regards to tightening the bolts. How can I get it tight enough to get rid of wobble but lose enough to allow for expansion? Should I use washers? What type?

Thanks again.


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## muleskinner (Sep 24, 2011)

Just my 2 cents worth, but I'd bolt those legs on with a rectangular bolt pattern - 4 or 6. That's a better stabilizing pattern than a single line of bolts. I'd also think about using inserts and machine screws instead of lag bolts.


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## sbjmg (Aug 23, 2012)

I will be doing them in two rows as Doss suggested, in regards to your insert idea how does that help/allow for expansion?

Remember I am a complete novice so please talk to me as if I were a 10 year old.

Thanks again


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## muleskinner (Sep 24, 2011)

Because I'm the dad and I said so.

Actually, the machine screws and inserts are just my preference. I always think of lag bolts for picnic table and work benches, not dining room tables.


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## Cosmicsniper (Oct 2, 2009)

My thought on this is that screws are generally fine…the fewer mounting points, the better…which is why table tops are usually screwed to a table as opposed to glued. Glue is what keeps the table from expanding and contracting.

But the problem is that the fewer points of contact you have with the top, the more likely the boards will cup. I would be very concerned about being able to keep the table flat. Of course, this is why breadboard ends are common. I'd explore that option…or screw some splines underneath.

As far as slotted holes in the metal, that's probably a good idea, but locking them down is okay…the idea is that you can just relieve the pressure every now and then, though I think by the time that's a problem some of the top will be coming off the table.

Just my $.02.


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## Cosmicsniper (Oct 2, 2009)

Btw, the thickness of the walnut is definitely in your favor…it might not cup as much as I think.

Welcome to the most difficult and mysterious part of woodworking!


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## Doss (Mar 14, 2012)

Yeah, you could probably snug it up pretty good, but not so much you're at risk of pull the wood out of the top (the screw will act like a drill bit if you apply too much torque).

I'd use washers but that's mainly because I use them in a lot of situations.

Depending on what part of the log the boards are from (and what type of stress that part was in), you may get cupping or movement like *Jay* said. Then again, you may not.

Post up a pic some time.


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## LeeBarker (Aug 6, 2010)

There's a considerable amount of overthinking going on here.

First of all, you don't need slots, you just need slightly larger holes. And washers. There. That saved you an hour or two.

I can't imagine a 4" wide mounting plate being inadequate. Fasteners would be along the long edges, in pairs.

I would steer away from lag bolts. I've broken more of those than I have good quality cabinet screws, by far.
Inserts are sexy, but often come back out when they're asked to release from the machine screw.

Plan your pilot holes carefully (sizewise) and lube your screws.

Nice design, great wood choice, and cease worrying and start enjoying.

Kindly,

Lee


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## Cosmicsniper (Oct 2, 2009)

You're definitely right, Lee, but I'd rather over think it than to under think it. I've seen table tops expand 1/2" over a season and others cup like crazy. My biggest concern was the width of the boards being used. 11" wide boards and 40" wide table could be a problem…but yeah, I'd concur that attaching with screws isn't a big deal…as I said, most table tops are attached that way for a reason.

In lieu of breadboards, some table makers who prefer the exposed end grain edge will reinforce this with a rod through the table. Of course, that's a tough hole to drill for guys like us, but it does demonstrate that designs do have to account for such wood movement.

In truth, the table may not move at all. But wood is finicky. I planed 3/8" off a 4/4 walnut board last month and the sucker cupped overnight 3/8" over it's 9" width. There can be a lot of energy in wood, which can be triggered over time with moisture…or by just changing its shape.


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## LeeBarker (Aug 6, 2010)

Good comments, Jay-Illustrating the beauty of LJs and the resources it represents.

That was one stressed piece of walnut. Leave it a couple more days, and it might be saying one syllable words and short sentences.

Kindly,

Lee


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