http://wiki.bowlingchat.net/wiki/ima...lled_Balls.pdf
Not sure if the link will work so I copied and pasted also.


The Truth about Drilled Balls
By
Mo Pinel, MoRich Ball Designer and Advanced IBPSIA Cerification Lead Instructor
As an industry we have promoted the importance of the mass properties (RGs and
differentials) of undrilled balls for years, but how much do those specs. really
matter to the motion of a drilled bowling ball as it rolls down the lane. NOT A
LOT! What really matters is the characteristics and the surface preparation of the
coverstock and the mass properties of the drilled ball (the RG of the Positive Axis
Point and the intermediate and total differential).
The coverstock characteristics are controlled by which coverstock you choose and
what surface you choose to use on it. Unfortunately, that’s mostly trial and error
after assimilating all the marketing material you can find about coverstocks.
That’s a subject for an entirely different article which needs to deal with the
science of coverstock technology and a discussion about the truth in marketing.
This article will discuss the effect of drilling layouts and weight hole size and
location on the mass properties of drilled bowling balls and, therefore their ball
reactions.
Are there any people who care about how undrilled bowling balls roll? I THINK
NOT! The decisions made about the layout and the size and location of the
balance hole have a very significant effect on the reaction of the drilled ball. A
complete layout of a bowling ball consists of two components. They are the
drilling system used and the balance hole size and location. The drilling locates
the pin and the Preferred Spin Axis in relation to the bowler’s PAP. This
represents about 35 to 40 % of the drilled ball’s reaction controlled by the mass
properties. The remaining 60 to 65% of the drilled ball’s reaction attributed to the
mass properties is controlled by the size and location of the balance hole.
The drilling can be done accurately by using either of two systems. By swinging
arcs from the pin and the PSA to the bowler’s PAP and the Vertical Axis Line is
one way. The other way is to use the “Dual Angle Layout Technique” which can
be found on www.morichbowling.com. This is the system that I prefer. Any
accurate drilling system must take into account the location the pin (low RG axis)
and the PSA (high RG axis) in relation to the bowler’s PAP and the VAL.
I suggest using the “Gradient Line Balance Hole System” for controlling the ball
reaction by locating the balance hole properly. It can also be found on
www.morichbowling.com. The closer the balance hole to the PSA, the stronger
the resulting ball reaction. The bigger the balance hole, when it’s located near the
PSA, the stronger the reaction of the drilled ball.
We prepared the following chart for the MoRich FRENZY to show how much the
mass properties of drilled balls change from those of the undrilled ball by using
different drillings and balance hole locations.
The layouts used in the chart are “Dual Angle Layouts” and the balance hole
locations are “Gradient Line Balance Hole” locations. If you look at the chart
carefully, you will notice how much the differentials change from layout to layout
and from the drilled balls compared to the undrilled ball. Bear in mind that the
total differential controls the amount of flare of the drilled ball and the
intermediate differential controls how quickly the drilled ball reacts to lane
friction. The larger the total differential, the more the ball flares causing the ball
to react sooner. The larger the intermediate differential, the quicker and sharper
the ball reacts to lane friction when it encounters it. Let’s look at these drillings.
The 80x2.25x50 layout with no balance hole has both the lowest intermediate and
total differential of all the drilled balls, therefore, it will be the smoothest and least
hooking of the drillings listed. The 85x3x40 layout with a P2 balance hole has
slightly larger differentials and, therefore, will produce a medium ball reaction.
The other two drillings have substantially larger differentials and, therefore, will
produce much stronger ball reactions. The 30x4.25x20 layout with a P4 balance
hole has the largest total differential and will, therefore, react the soonest of the
drillings listed. The 65x4x30 layout with a P4 balance hole has the largest
intermediate differential and will have the sharpest breakpoint of all the drillings
listed. There will be a VAST difference in reaction between these four drillings.
Keep in mind that adjusting the surface of the drilled ball to change the surface
roughness of the ball will allow you to move the break point closer to the foul line
or the pins in order to change length of the skid phase of the ball. The shape of
the breakpoint is due to the ball chosen and the drilling used and the balance hole
size and location employed.
I hope this article gives you an insight into how differently the same type of ball
will react with different layouts and balance hole locations. These are your tools
for dialing in the ball for each bowler and, therefore, increasing their enjoyment
of the game.