Making good quality Scrabble tiles from scratch was perhaps a little too ambitious, but making labels to stick to existing Scrabble tiles was definitely an option.
This instructable uses an inkjet printer to print the stickers, and a Cricut paper cutter to cut them to exactly the right size to stick to the Scrabble tiles. You'll also need a rotary guillotine (or a metal edge at least a foot long plus a sharp cutting knife - either a scalpel or an exacto knife)
By the way I'm using the old-style plastic tiles that came before the wooden ones in the USA. These are still the current design in Europe and Mexico. (You can find them on eBay fairly often; I bought mine in Mexico which is just a few miles away from where I live)
(This technique should be possible with the wooden tiles but the artwork will have to be created differently to match.)
Step 1: Print the replacement tile tops
These images must be printed at 600dpi to be the correct size for the tiles.
Because of the size of the image you will probably get a warning that 'some clipping will occur' - that's OK, it's only a couple of millimeters outside the area that will be cut out to make tiles.
The tile image looks a little pinkish on my screen but as you can see from the photograph of the board, they printed correctly in yellow at just the right shade to match the plastic tiles. If you don't get such a good color match, you might have to tweak the color of the images in your drawing program before you print them.