Good solid planning is best in this and if possible use an expendable rotor to use for the first one you do. Normally we all ready have a pattern for cross drilling so we just use a transfer punch for each of the holes according to their size, but this is how it is done if there is no pattern.

You will need to have a heavy duty drill press with an index-able table (table that you can spin on center). If you use a small drill press it will take quite some time to complete this and will probably beat up your press.

For Honda rotors we used a upper neck bearing cup and a rear axle with a tapered head to give us an acceptable center.

Once we were sure that we had a reliable center we drilled and tapped the table so we could use the 12 mm bolts from the handle bar mounts to bolt it to the table.

When we set up a new rotor we use all of these parts again. Using the cap and axle allows us to get our center. There is some gap between the bolts and the rotor holes so finding center each time is important.

Using a cam shaft degree wheel we map out the vent runs. For simplicity we will only cover the straight vent runs here. Staggered vent runs are difficult to map and keep accurate, do yourself a favor and do not try one of these first.

This is figured on 18 vent runs.

I map out the first 9 based on the spokes of the rotor. Using a marker and a straight edge I draw the lines where the first set of vents will be orientated.

Now double check using a caliper to make sure the spacing will be even all the way around. Now half your measurement and start making your second run of vent lines.

Now that you have all of your lines drawn make a measurement across the surface of the rotor from the spokes to the edge. Divide this by three and make reference marks on one line at the thirds.

Now put your marking in the drill chuck and lock it in place. Put the table back under the drill chuck and line up the tip to your first reference mark on the vent line and lock the swing on the table and make sure the rotate is loose.

Going around the rotor lower the marker to make your cross reference marks at every other line. Don’t just spin the table as this will make you other reference marks confusing latter. When you are done you should have a bunch of crosses at you reference points for the vents. Use this same technique for the other marks.

There are literally hundreds of different ways of mapping out this rotor this way. You could skip the marker process and chuck up a spring loaded center punch instead so that each time you bring the drill head down it makes the center punch mark saving you a step.

At this point you can center punch all of your intended holes. I usually do not but this may help you with another level of accuracy.

Because you are dying to: Let’s get drilling….

BEFORE YOU START DRILLING

1. You must know the speed of your drill bit. This is imperative to make sure the bit will last a reasonable amount of time. Mis match this and you can kill any drill bit with in seconds.

2. When drilling your holes do not lean on your drill press handle. Putting too much pressure on the

Here we have the lines for all of our vent runs all drawn out.

I used 1 rivet at each rotor spoke and the center of the spoke hole on the opposite side to make the lines all line up correctly.

Before you begin drilling know the speed of your drill bit.

5/16" is safe to about 300-400 RPM. Later when we move to the 3/8" or larger bits we will be moving to a slower drill press. Turning your drill bit to fast will destroy it very quickly.

Now we have to lay out the first series of holes. We are doing a staggered 3-2 pattern

So our first measurement we will need to know is total width of the rotor braking surface.

In this case we are doing a Honda CB500 rotor so the total distance across is 1.84", so center of the rotor is about .92". You can see in the picture that we have made our center mark on the rotor. Because our table is index able we will only need the one mark for reference. Then for the other 2 holes of the run 1/2 .92" and you get .46" from either edge of the rotor surface.

Here is where you will want to make sure your marks are accurate. Once you start drilling it is very hard to correct a problem hole.

Here we have the first series of the holes drilled at 5/16" in the center of the rotor face. Remember to drill only one circle of holes at a time to maintain accuracy and make use of your drill presses rotating table.

Here we have the second series of holes done.

Now we have the whole 3 sequence done.

Now comes the time to plot out the 2 series holes.

These must be centered between the spaces of the holes we just drilled.

You need to know what you are after before you start drilling. Do you want them all one size? Or maybe alternating between 2 sizes. It is always best to select them a little small when starting out. You can always drill it bigger for visual effect and performance later.

I usually start out with a 5/16 bit. If all my drill spots are pre-mapped I leave the rotate table and swing loose clamp loose. This lets me jump around the surface of the rotor faster and get it completed faster. I have done many of these so this just comes natural.

FOR THE OTHER HOLES:

At this point you can use the same pattern as you did before or you can find center between any two in the same string of the three hole pattern. And this will be the location for the 2 hole part of the pattern.