Lag bolt construction, is this a bad idea?

I like the simplicity, but I think they would move on the pivot.  Perhaps using two lags per attachment point or dowels, biscuits or dominos. 

Not the same as your design, but I followed the following plans ... http://sites.google.com/site/mybiggreenegg/home ... and used two carriage bolts per attachment point.

Here's a progress shot.

Richard - I think you have fixed your racking problem and I suspect it won't move.  I'd still put in dowels in the upper points though. 

Thanks for the comment - the wood is Philippine Mahogany and boy is it heavy.  I'm kinda wishing that I stuck with 1x4 for the majority of the framing.  The top and bottom are not solid, but individual planks clamped together.  I will be fastening them to the frame with Kreg screws from below.  I was debating leaving space between the boards, but I figured the table will be covered when not in use and I will be finishing all sides of each board before assembly.

The inset is black with gold speck granite (two pieces glued together with silicon adhesive) to make up the right height.  Home Depot - about $4.25 per 12" tile x 2.

I'll post a whole thread when I figure out how to start a new thread.

I agree w/ Stike. A "moment" is a fancy (Engineering) word for "torque" - it's basically the "pivoting" you speak of.

ANY connection w/ only 1 connection point can (will) produce a moment.

If I may be so presumptuous, I'd say you wanted to use the lag bolts because they were the only things long enough in order to be able to span the distance of, and connect, all the pieces of wood w/ 1 long bolt, right? And you thought the lag bolts would be "stronger" right?

Well, if that's the case, it looks like your "legs" are 4x4s? If so, you don't really need those, that's overkill. 2x4s will suffice. However, if you wish to use 4x4s, and you can't find normal screws that are long enough to span the 3 pieces of wood, then I'd suggest going w/ a smaller diameter lag bolt & doing 2 of them (2 connection points stops the "moment" force being generated).

And to piggyback what Stike said regarding the wood splitting - I am by NO means a carpenter, and my "finish" carpentry skills leave a LOT to be desired, but what I always do is drill pilot holes first, which helps decrease the chances of splitting the wood.

Anyway, HTH,
Rob

HH... not to nitpick again hahaha
but you can have a pinned connection that has no moment.  just needs to be triangular (which is why a cross brace or wire would work. though it may not look ideal)

Stike - well, technically, true. Sorry, should have been more precise. Was talking about 2 members pinned by 1 connection, wasn't talking about 3 members w/ 3 pinned joints which form a rigid constraint because of the geometry of them all being aligned in that manner. The leg & the horizontal board in the table would be 2 members, and would have 1 pinned connection (in the OP's example).

Adding in a 3rd member & aligning them in that geometry, and you're basically talking about a strut, which, because of the geometry, restricts the degrees of freedom. Each pinned joint, acting by itself, will allow the moment - however, when placed in the configuration you're describing, the moment is restricted because it's being pinned by the other one and it's rotation is being restricted - it's not the "pins" of any one joint restricting the movement, it's the geometry of all the joints acting together.

Take your 3 straws example, and, instead of putting it in the shape of triangle, put it in the shape of a "Z." In that case, there will still be a torsional degree of freedom allowed on the upper & lower "legs" of the "Z."

You can also take those 3 straws, and stack them on top of 1 another such that 1 pin can go through all 3. That pin would allow rotation of all 3 around the single pinned joint.

So, agreed, I should have been more precise w/ my statement that "any" pinned joint will allow rotation, but agreed that you're also being nitpicky ;-)

^5 - good catch!!

Richard - Just to make sure it's clear, you have at least 2 choices:

1.) Use your original design

2.) Redesign the look of your table

If you wish to use the design you originally submitted, a way to do that is by using 2 screws (or, as Stike suggested, dowels) instead of 1.

I "assumed" you wanted to use that design (because that's what you submitted), and thus the advice was given based off that assumption.

If you wish to change your design, then you can utilize the diagonal cross-bracing suggestion (or even guy wires, cementing the legs into the ground, adding gussets, making it out of welded steel, etc). Heck, if you're really worried, you can spend more on your table than you did your Egg to ensure it's stability.

Finally, while it's still a possibility for the "racking" using 2 screws, my personal opinion is that it's a SLIGHT possibility based off of the function of the table.

After all, it's going to be holding a grill & possibly being moved infrequently - it's NOT going to be holding nuclear bombs and being pushed & pulled on w/ any great force or regularity. More than likely, if/when the "racking" occurs, it's going to be several years down the road, at which time the wood will probably be faded & in need of repair/replacement anyway.

Sometimes the best becomes the enemy of good enough.

HTH,
Rob