I should have done a video on it.
It is very simple really. I'll see if I can explain it step by step clearly. If you don't understand, please let me know.
Items required include: 3/8 inch socket and driver of some sort, Pencil Compass, 1/8 inch drill bit, 3/16 to 1 3/8 inch step drill bit, drill motor, pencil compass.
1. Remove your guards.
2. Wipe them clean on the bottom contact areas so they will make a good flat contact on the work surface.
3. Find the distance between the roll over at the top where it makes a tapered area down to the bottom ridge. You'll be finding the width of the flat area that wraps around the guard where you see the holes in my cover . Once you have found the distance, divide it by two, set the pencil compass so that it scribes dead center.
4. Once you have this center point located and the compass set, place the pointed side of the compass on the work surface against the very bottom of the belt guard and the pencil side on the belt guard in the center of the wide flat area. Keep the compass vertical, drag the pencil against the belt guard while holding it upright and perpendicular to the world.
5. Once you have the line drawn, lay the guard back over your deck and align the guard retainer holes over the holes in the deck.
6. Stand back, square up with the deck at a 90 degree and find the center as if you're making a ninety degree line from the mower frame rail to the center of the round area near the pulley area.
7. Draw a thin line to mark that center. It will appear off center once you pick up the guard. That is fine as it is where you want it.
8. Drill the 1/8th hole where the two lines intersect.
9. Using the step drill thru the guard until you are slightly smaller, your choice, than the flat surface and then chamfer it with the next size step. Do not drill thru.
10. Turn over the guard, chamfer the back side.
11. Lay a measuring device at the edge of the first hole, measure over .750 thousandths (3/4") and make a mark. Repeat your first 10 steps until you are satisfied with the amount of holes required to blow out the guard efficiently.
There you have it. Happy hole drilling.