18mm is overkill and will add a lot of weight. Better to buy 9mm ply for the base and save the 18mm for other jobs. your draws are large so heavy already.
For an 'amateur' 9mm ply screwed and glued is quick and easy for a garage , I recently re-bottomed an old cheap chest replacing hardboard and found 9mm ply screwed and glued was quick and simple for a garage.
If you plan to put a very heavy load in one draw (say the lowest one)i then use the 18mm on one of that one re-infoced batten on that draw only or rebate it in if you have the tools. But for a simple job in a garage you will get away with screws and glue.
Consider what is going to stand on top of the chest? If its something heavy like a pillar drill or vice, then use the 18mm ply to reinforce the top to take the weight and put the heavy things near to the vertical supports ie an edge (or middle if you have two bases joined in the middle.) Otherwise the whole top can bow in. Good luck
For an 'amateur' 9mm ply screwed and glued is quick and easy for a garage , I recently re-bottomed an old cheap chest replacing hardboard and found 9mm ply screwed and glued was quick and simple for a garage.
If you plan to put a very heavy load in one draw (say the lowest one)i then use the 18mm on one of that one re-infoced batten on that draw only or rebate it in if you have the tools. But for a simple job in a garage you will get away with screws and glue.
Consider what is going to stand on top of the chest? If its something heavy like a pillar drill or vice, then use the 18mm ply to reinforce the top to take the weight and put the heavy things near to the vertical supports ie an edge (or middle if you have two bases joined in the middle.) Otherwise the whole top can bow in. Good luck
