We use 2 methods of raising tables to the preferred height: 1 : Find large coffee cans and fill to the desired height with redimix concrete. Allow to harden. Then, just set the table legs down on the concrete. The weight of the cans will make them very sturdy.
2: Buy PVC pipe wide enough for your table legs. Cut the pipe square across the bottom. Tape the 4 pieces of PVC pipe together. Mark the spot to drill. Drill a hole the same height in them. Put a stove bolt through the holes and fasten a nut on the side. Put 2 holes in the pipe if more than one person needs to use the table. If the PVC pipe is large, it will be very stable as you work around the table. Hope this helps.