Step 1: Starting Your Design

You will need to click the button Primitives on 123D design and select the cube. Once selected you will need to change the width and length to 50 and the height to 35.

Step 2: Measure Your Pencil

Take your slide caliber (or pencil) and measure the diameter of the thickest part of the pencil. It should be (roughly 8mm wide)

Step 3: Adding Your Pencil Slots

Once you have gotten your measurement, then go back into 123D design and add cylinders. For the width of the cylinders, make it your measurement diameter (8 mm) or radius (4 mm), for the height make it 20 mm make sure it is centered on a multiple of 25

Step 4: Making a Slot

Next you want to bring your cylinder and move it over your 3D square. To do this hit the move tool and drag it wherever you want COMPLETELY in the square. After you do this go over to the combine tool and select "subtract". Select your square and then select the cylinder you want to subtract. After you do that click away from the two objects and you will get an empty space. Do this for the desired amount of pencil holders.

Step 5: Final Touches

Once you have finished your pencil holes, you will want to get rid of all the extra plastic on the bottom of your object so that you can make it smaller. After that select each corner and select fillet and put in the number 4. This will make your design better. Then hit the D on the keypad while your object is selected to put it flat on the surface.

Step 6: Download

Now you can export your object as 3D and then select STL. After you do this select "Fine". Once this is done hit ok and it will take you to documents hit the drop down menu and select your drive. Then you are ready to print!