DIY Flexi First attempt.

Brian,
I built a double-Flexi several years ago and have used it since (check my system for pics). Drill the holes 1.5" from corner to center which is 1" from side to center. This leaves enough material around the connection point to be strong. This distance also works well if you put 1.75" fender washers against the shelf and under each nut. The washers then leave just a few mm of surface reveal between the washer and the edge of the shelf.
Have fun building!
Doug

I'd recommend a forstner bit to cut the holes, and a drill press if available. The forstner will cut nicer holes than any other hole saw or speedbore type bit. Happy flexi-ing.

-Richard

If not too late, I recommend increasing the size of the rods to 3/4 inch. I've built two of these racks. The first was built with MDF and the second was constructed with slate (check my system). The MDF rack would wobble some if the nuts weren't tight while the slate rack is "rock" solid. Although the 5/8 inch rods provide enough strength I regret not using 3/4 inch rods.

Brian-
On a couple of the racks I have done, including one that is supporting a 350lb turntable, I drilled 3.5" in from the front and back edges, and 1.5" from the sides - to the center of the rod. If you want to go to 3/4 as some suggest, you may need to adjust slightly.

A good rule of thumb is to keep in mind what will be housed on the shelves, and keep a minimum clearance for standard 19" width components between the rods/nuts/spacers....

I build a two Salamander Archetype clones flexi-racks,and I wasn't happy with the results,the flexi-racks were unstable and wobbly.Here is my suggestion.The distance of the hole from the edge should be double the hole diameter.Go for 1" or 1"-1/4 rods brass or stainless steel.The shelves could be 2" or thicker maple,for hardware get a machinist to turn some donut shaped brass fateners instead of regular "nuts".See the Mapleshade Samson rack for inspiration.Yes it won't be cheap but quality never is.
Regards
George