It doesn't look like it will be a very wide table.
I wouldn't worry too much 1/8 inch over both sides of the screw ?
How much of the top is flat sawn would be something to consider
Good Luck

 

There are several calculators on the internet that will calculate how much wood will move. Put in the species, width and moisture content that it is now and the highest moisture content that you think it will acquire in the calculator and it will tell you how much it will move. Use the answer to determine the size of the elongated hole. A 30" piece of white oak at the low moisture content of 8 and the high content of 11 will move 0.3375" or 11/32" according to the calculator.

https://www.bing.com/search?q=woodweb+shrinkolater&cvid=f4d9fd1604e3497fbf78fa71c9391c0d&aqs=edge..69i57j69i64.14039j0j1&pglt=43&FORM=ANNTA1&PC=U531

 

A more elementary follow on question.

The hole should be elongated like a slot, correct? How exactly would you drill that?

 

The hole should be elongated like a slot, correct? How exactly would you drill that? - leftcoaster

One method is to use counter-bore router bit like this:

https://www.whitesiderouterbits.com/products/sc102

Best Luck.

 

It would be easiest to use figure "8" fasteners ing the tops of the ribs. 3-4 in each rib should do it. Or, you could cut a groove in each rib with a router and slot cutting bit and use "z" clips or wood buttons. If you want to drill through the ribs and use long screws, then simply drill oversized holes and then put a washers under the screw heads to span the oversized holes. As 4wood said, you can use an online calculator to see how large the hole needs to be.

 

It would be easiest to use figure "8" fasteners ing the tops of the ribs. 3-4 in each rib should do it. Or, you could cut a groove in each rib with a router and slot cutting bit and use "z" clips or wood buttons. If you want to drill through the ribs and use long screws, then simply drill oversized holes and then put a washers under the screw heads to span the oversized holes. As 4wood said, you can use an online calculator to see how large the hole needs to be.

- bilyo

+1 on the figure 8s. I initially thought that you could use Z clips, but I'm guessing you don't want them to be visible from the side.

Figure 8s would solve that and give you the movement you need.

 

You can make the slot 1/8" for every foot of table width. The center holes don't need to be slotted, just the outer holes.

Cut them with a router bit.
Or you can drill overlapping holes with a Forstner bit.

Good luck with it.

 

For the figure 8s the smaller end gets attached on the top?

 

For the figure 8s the smaller end gets attached on the top?

- leftcoaster

I don't know if it matters but I put the smaller end on the apron because mine are 3/4 and I can drill a smaller counterbore.

 

For the figure 8s the smaller end gets attached on the top?

- leftcoaster

I don t know if it matters but I put the smaller end on the apron because mine are 3/4 and I can drill a smaller counterbore.

- Woodknack

I found a set of instructions online that confirm your approach. Thank you !