How to make a DIY toy storage box with casters

I made this rolling cart out of 18 and 9mm birch plywood. It has four casters and a removable carved letter made with the CNC machine. 

I didn’t have any 18mm plywood in the shop. So I got it precut from a shop.

I glued and nailed the sides of my box, using my air powered nail gun.

For the bottom I used 9mm plywood. I used my circular saw and a guide rail to cut the bottom slightly larger than needed.

I then glued and nailed the bottom in place. I used a flush trim bit on my router and flush trimmed the bottom of my storage box. 

I used some wood filler to cover up any imperfections on the piece. 

I then used my random orbit sander to sand the box. I begun with 80grit sandpaper and finished at 180.

To prevent the wood from splitting I clamped a plywood scrap piece on the back of the hole I was going to make. I drilled the hole using a forstner bit.

I then started the paint job. This whole thing was a matter of good masking. I had to make a synthesis of triangles from different colors. I prepared each color and then used masking tape to make the masks. In order to have a really sharp edge here, it is best to bush from the tape to the inside of the form. If you brush against the tape, there is good chance you’ll mesh the sharpness of your painted form. I applied two coats of each color and used my heat gun to speed up the drying process. I used latex paint.

I then used a scrap piece of wood as a spacer to mark the positions of the casters. I screwed the casters in place. Two of the casters have stoppers.

To customize the box for your kids, you can can carve the initial letter of your kid on a piece of plywood. I used my CNC to do that. I then painted the inner carved forms. After the paint was dry, I sanded it and it was ready.

I wanted the letter to be removable,  so I came up with a simple mechanism that uses a rubber band and a dowel. 

At this point my little box was ready, I hope you like it!