Lag bolts vs. carriage bolts

[GonnyGump]

Bottom line: Which is stronger, lag bolts or carriage bolts?

Context and details: I am building a large (12' long) oak dining room table, the base for which will be two 18" diameter circular columns. Each of the columns will sit on a 20" circular "plate" (about 4" thick) that, in turn, will be supported by four scroll feet. The scroll feet will be cantilevered out from the plate by about 6". My question is how best to secure feet to the plate. The two options are: a) 4-1/2" lag bolts up through the heels of the feet and into the plate; or b) carriage bolts following the same path through the feet and plate and secured with a nut countersunk into the top of the plate. Can anyone advise me which will be more secure, both structurally and against any potential wood movement?

Thanks in advance for useful insights and comments.

jdc

[Dan Parrell]

[bridger]

can you make the feet from continuous members? that is, opposing pairs of scrolls cut on the ends of a 32" long board. half lap where they cross, run a fastener through there into a cross brace in the column. the load there would be so low it wouldn't matter what you use. it would just have to be enough to carry the feet along if you picked the table *up*

[GBsCards]

Is it just me?? I thought (and I could be VERY wrong) lags were screws, although they could be very big screws. So what the general public refers to as lag bolts are actually lag screws. Either way, I thing the screws would be better. Bore the same diameter hole through the legs and a smaller diameter through the columns to draw it up real tight. Just beware of overtightening.

[RB]

Since you have a 20" dia plate I'd be tempted to put a "real" load bearing surface in the center of the plate (assuming that it won't be visible) and regard the scroll feet as only semi functional feet. In this case they could be fastened to blind nuts, perhaps hanger bolts in the feet connecting to threaded inserts in the bottom of the 20" dia plate.

RB

G> Bottom line: Which is stronger, lag bolts or carriage bolts?

[CW]

Yes, they are screws. Carriage bolts would be better. Better grip.

overtightening.

[GonnyGump]

Thanks to all for the feedback. Love the web... acquired most of the knowledge I most value about woodworking right here! Here are some responses.

Lag bolts are indeed screws, as others have noted. Sorry... I supposed I was primed by the misnomer posted over the bin at which I bought these at the local home improvement warehouse.

Considerations of assembly-disassembly have entered my mind. While I agree in principle that the c-bolts are better in this regard, they would be less convenient for my particular configuration: The column will overide the countersunk nuts in the plate, so to get to them (to tighten or diassemble the feet) I would have to remove the columns. Not so for the lags.

Now THAT would have been a good design. Wish I can say I had thought about this in advance, but didn't. Nevertheless, I'm not sure it would have worked, given additional details not mentioned (the specific shape of the feet, constrains introduced by veneering, etc.). However, most appreciative of the suggestion, which I hope will inform future exploits!

[Darwin]

How about using threaded brass inserts into the base, then bolt through the feet?

columns

anyone

[bridger]

hey- aren't carriage bolts just machine screws with funny heads?

Bridger (who'se in a smartass mood this AM)

[GonnyGump]

Since such inserts are usually much shorter than the lag screws that can be used, I would guess that they would be less secure than the lags.

jdc

[Darwin]

You're right that they would be much shorter.

With that said tho -- they would be inserted into your base, into the face grain. I've had really good luck with them; sometimes they can be a PITA to install. Plan their placement; with out looking at your design; I would say a couple in each foot would be needed to keep them from torquing.

FWIW you'll want to make sure you get the "right" ones, some have very coarse threads like a lag bolt except sharper, others have a more fine thread, similar to a course stove bolt, but sharper. I like the ones with the course threads, I found them easier to install, and don't crush the wood quite as easily. Others may have their preferences.

Good luck...

[Danny Boy]

For similar size, similar circumstances, bolting is stronger. Also, later, bolts can be tightened. The real question is does it really matter in your case?