Sandwich-type harmonica made from recessed reedplates
Harmonicas like the Lee Oskar, the Hohner Special 20 and the Suzuki HarpMaster (Bushman Delta Frost) have a "recessed" plastic comb that surrounds the reed plates. Your lips don't make contact with the front of the reed plate, instead, they are in contact with the plastic comb. To replace the stock comb with a "sandwich-type" comb, you need to round off and smoothen the front of the reed plate so that it's comfortable in your mouth.
Here's how you do it
Start with some fine sandpaper. Sand down the draw reed plate as described in the document "Preparing a reed plate for use with a flat comb." This gets rid of the protruding riven ends and allows the reed plate to sit properly on the comb. It makes the harmonica more airtight and is recommended on all harmonicas, even Suzuki harmonicas which have no rivet ends.
Next, hold the reed plate at an angle and sand the front edge of the reed plate in a circular motion.
Next, do the same to both sides.
Using a piece of 600 grit (or higher) sandpaper and polish the front edge. Be sure to avoid contact with any reeds.
Place the side of the reedplate on your working surface and run the 600 grit sandpaper back and forth over the edge. You are making a nicely rounded edge along the side of the reed plate. Don't be afraid to rub pretty hard. Just be sure to not catch any reeds when you work on the draw reed plate.
Once you are done, the corners should look smooth and comfortable.
This is a very comfortable and airtight harmonica made from Suzuki reed plates with a sandwich-type comb and a set of Special 20 cover plates. You can't buy a harp like this in stores!
Special note regarding Lee Oskar harmonica comb swapping:
The cover plate on a Lee Oskar just barely sits on the edge of the reed plate. When converting a Lee Oskar harmonica to a sandwich-type comb, moving the cover plates back will help improve airtightness. A very easy way to accomplish this is to enlarge the cover plate holes. Simply drill the existing holes with a 1/8 drill bit.
Once assembled, you will be able to position the Lee Oskar cover plates further back.