Flat pack / interlocking design question

I'm trying to make a flat pack interlocking chair but cannot figure out how to get the bottom pieces from falling out when right side up.  If I want the chair to have a uniform square shape, I don't think I can make the locking cuts at any angle.....so, the bottom keeps falling down.  
Below are two examples of interlocking that confuse me.  The first is a link to the table upside down.  The second is a link to the table right side up.....Can someone please explain how the long pieces which are in the "under" position of the lock do not fall out when turned right side up?



Picture of Flat pack / interlocking design question
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Chasingthesun73 (author) 5 years ago
Thank you all for your help. Great suggestions....and good eye Rick- I never would have caught that!
rickharris5 years ago
The 5th leg back and I guess the same at the other end appears to be put in from the bottom holding the long rails in place when the assembly is turned over and weight is applied. The rails merely act to separate the leg segments and support those not touching the ground..
CTS-Chris5 years ago
also looking closer at the design and even number of ribs were used this would make it easy to conceal the use of a offset (opposite) cut every other rib it would all "lock" in then here is a pic roughly showing the long cuts the second shows the locking planes once assembled this would keep either side from being "top" or "bottom"
rib opp.pngrib opp 2.png
CTS-Chris5 years ago
another option I have seen with flat-pack designs is to make one piece that locks the whole assembly together . an off cut that is the "center piece" this will hold the two intersecting planes of the cut pieces together like a giant skewer
canucksgirl5 years ago
I agree with Steve. Other than tight joints or using glue, it does appear as though the intersecting pieces (to the series of "U" shaped pieces) would fall out. The only other option would be to make the cuts to the long pieces on the opposing side so that they connect from the top versus the bottom. (I'm assuming your cutting the pieces?)
Tight joints ?
Glue ?
You could deliberately slightly angle the slots in opposite directions on each piece, automatically making the joint tight as you drive the cross member in. It might be barely perceptible.

A similar method I've seen is to put a "nub" on the inside of the slot, which makes a tiny section of the slot narrower than the thickness. Pound the pieces together for a tight fit.
Yes, that would work too.