You need to make some investigations to discover exactly what's happening...
First check the table frame against the floor - is the floor level and are the legs all of the same size? Very unlikely for the legs to be different lengths. You can check for this by rotating the table.
Next check the table top relative to the frame - is there movement between the two? i.e. when the table wobbles is the whole table moving or just the table top moving while the frame remains still?
Does the table top wobble only when it's extended or does it wobble when it's closed up?
When you have this all worked out then you can think about how to fix it.
Be aware - table tops are not always fixed rigidly to their bases - to allow for shrinking and stretching of the table top and to stop it warping - tops often have slightly loose attachment to the frame - these can sometimes loosen and allow unnecessary wobble - you will need to peer underneath perhaps with a torch.
Finally - if your table is antique - as in very old - there may be wear in the extending mechanism - check for this - if the table's valuable consider a specialist repair.
Good Luck..., February 2016
