I am designing and building a hardwood coffee table, simple design, hardwood top, 3″x3″ legs. My question is what is the best way to mount the legs. I was hoping to avoid using an apron or spreader. Trying to maintain a clean look. I realize I have to allow for the wood to move. I would appreciate any suggestions or ideas. I attached 2 images from my sketchup design.
Thanks
Replies
Your design has to manage two issues - keeping the top flat, and coping with racking forces.
The easy option is to make the legs into squares and screw through them into the table top. You will need three pairs of screws each side of the cross-piece. A central pair and one at each end. Pairing will help with racking. Elongate the holes to allow for movement.
An alternative is to cut through tenons - these will often be wedged for effect. This is a harder option but will look better, but you will need to lose the lower piece or accept the possibility of joint failure due to wood movement in the top.
The youtuber's choice would probably be to rout C-Channel into the base of the top and fix it first to the legs, then to the top with threaded inserts.
As rob says, close the legs into full squares. Make the corners bombproof with dovetails or box/finger joints. Screws in center are fixed, outside sets elongated holes. To help with racking add an "outrigger" at the top of each leg pointing to center. A 6" leg with a bridle or M&T joint and a couple of screws into the top will help a lot.
Thanks for the input. I was thinking of adding a stretcher, it really won't be visible. Then either using slotted screw holes as rob_ss suggested or something like figure 8 clips. I also plan on using a tenon joint on the legs, I don't feel too confident making box joint or dovetail joints yet. I'm using pricey wood so I'm being cautious. I attached another image.
You can most likely also use figure 8 "desk top fasteners". I am currently working on a table which does not have aprons and the suggested way to mount the legs to the top are these figure 8 fasteners. You can buy them at Rockler - https://www.rockler.com/desk-top-fasteners
The way they would work is to imbed them into the leg by using a forstner bit to drill a shallow recess just the size to fit one side of the fastener so it is flush with the surface of the leg. The side that is screwed to the table top does not have to be recessed. The concept is that the the figure 8 fastener will rotate with expansion and contraction so the ideal way to install them is angled so the expansion/contraction will rotate them. They shouldn't be screwed too tight or I suppose they won't rotate.
There are YouTube videos on installation and, while there are some differences in actual process in each the concept is the same.
I would say, however, that a much better table construction - more strength and flexibility is to fasten the top to the apron and use standard rectangular table clips. Again, there are videos online about installation with these table clips and I believe Rockler also sells these with instructions online.
To date, I have used the rectangular fasteners with great success. I believe the figure 8's will work also, but have not used them till now. In the case of the table I'm making now, the look of the table is superior without aprons, so, based on other plans I've seen and the videos online, I believe it will work well. (Sorry if this is confusing. Watch the videos and it will be clearer.)
Familiar with figure 8 clips, but not sure what rectangular clips are.
So your table doesn't have an apron, which clips are you using? You wasn't quite sure.
I am using the figure 8 clips on the table I am currently making, which doesNOT have an apron.
The other clips (also sold by Rockler, and others) are made to be used effectively on tables with an apron. A slot which matches the thickness of the clip is made in the apron. The clip slides into the slot and is attached by a screw to the table top. This allows the top to expand and contract freely across the grain because the part of the clip in the apron is not attached with a screw, but allows the wood to move. Rockler should have some online instructions for their clips which will show how to install them. Here is the link to Rockler's version of the clips -https://www.rockler.com/table-top-fasteners
You can also make your own in a variety of ways, which I'm sure you could find on YouTube or other sources online.
I have several tables with metal hair pin legs, three screws per leg. They work well.
I disagree that the top needs to be kept flat. This is a coffee table after all and looks to be relatively small. There is no need to keep it dead flat and I would not try to attempt to do so. It will likely stay reasonably flat all on its own assuming the wood used has been dried properly in the first place.
Now on to your other issues. I think your original design with U-shaped leg allows for wood movement just fine! As the table expands (or contracts) there should be plenty of "flex" in the uprights to allow that to happen with no issue. There is no long grain to cross grain attachment since you've located your long grain member all the way at the base and the "float" is taken care of by the flexibility of the legs.
Not sure what your skill level is, but I would suggest attaching the legs to the top with a mortice and tenon. Add a 1/4" shoulder all around to hide any mishaps and if things don't fit perfectly it's on the bottom after all! If your top is thick enough you should have enough engagement to have your table top act as the stretcher to prevent excessive racking. And this being a coffee table the height should be rather low which should further mitigate the racking issue.
Lastly I'll second the comment made about attaching the legs to the bottom rail. A box joint is a great option as are dovetails. I'd probably avoid a butt joint with screws and glue, but in all honesty that'd probably be strong enough too. Best of luck!
Thank you, this makes a lot of sense.