As an active member on bowlingchat.net, I see and help field a lot of requests for layouts and general advice about bowling balls, surfaces, etc. as well as a lot of some of the more technical details of bowling.
Lately, we’ve been seeing a number of questions about the Double Thumb Layout. This layout not by any means a difficult layout to understand. There are, however, a few simple pre-requisites that help to make the layout more accessible. One is at least a rudimentary understanding of the Dual Angle Layout Technique. The other is an understanding of the Gradient Line Balance Hole System. Both of these systems were developed by Mo Pinel of Morich Bowling Enterprises as a result of much research and C.A.D. work by Steven Freshour.
As another brain child of Mo, the Double Thumb Layout gets its name because to look at the final layout, it looks like there are two thumb holes in the ball. In reality, one hole is for the thumb, while the other is a balance hole (also known as an X-hole or weight hole). As it turns out, the placement of this balance hole is the key to the entire layout.
Let me give you just a little technical background. Recently, the U.S.B.C. undertook a large research project in the hopes of better understanding the complexities of ball motion. To do this they listed a bunch of known, controllable variables. The complete, ordered list can be found on page 13 of the results of the research. One of the most important findings from this research was that static weights (top, side and finger weight) played less of a role in the overall ball reaction than has been previously thought. It was found that the dynamic properties, such as total differential and the differential ratio of the ball had a much bigger impact than static weights.
So, what do the total differential and differential ratio tell us about ball motion. Well, the total differential tells us the flare potential of the ball, while the differential ratio tells us how quickly the ball will respond when it encounters friction.
As it turns out it is exactly these properties the Double Thumb Layout seeks to exploit and here’s how. Whenever we drill a hole in to a ball, we raise the RG value in that area of the ball. Why is this significant? Well, the bigger and deeper the hole, the bigger the impact on the RG profile. This concept lies at the heart of the layout.
When laid out properly, Double Thumb Layout places the PSA very close to thumb hole and the balance hole. The PSA is also the end point of the High RG Axis. Now, knowing that we can raise the RG profile in the area of a hole in the ball and knowing that the size and depth of the hole has a huge impact on the affect, by putting the High RG Axis in very close proximity to two VERY large holes (most thumb holes are around 2.5″ deep and between 3/4″ – 1″ in diameter), we raise the value of High RG Axis, which in turn raises both the total and intermediate differential, which in turn raises the differential ratio. Can you see where this is going?
Since total differential and differential ratio have a fairly significant affect on the overall ball reaction, if we can maximize those two values, we can create a ball that flares a whole lot and responds quickly to friction. What does that mean? The ball is going to hook!
One of the most confusing parts of the layout is how to actually determine the layout! Why? Because, using Dual Angle vocabulary, we are only given the VAL angle (30°) and the Pin to PAP distance (4″). We don’t have a drilling angle yet! The Double Thumb Layout instructions tell us to use an existing ball, mark the PAP and measure the required VAL angle and measure a point 4″ from the PAP. This is our “pretend” Pin. From there we mark a point 0.5″ from the thumb hole. This is where want the line from the “pretend” Pin to the PSA to pass through. When we draw the line from the Pin to the PSA, we can now measure the Drilling angle. And voila! We have a complete layout!
From there, we take those numbers and apply the layout to the ball we want to drill up. After we have drilled up the ball, all that’s left is to drill the balance hole. The center of the hole will be located 1.5″ from the outside edge for the thumb hole. Once we have found this location, we can drill the balance hole and the layout is complete! Remember what I said earlier about bigger deeper holes having a greater effect? To be the most effective, we must drill the balance hole AT LEAST 2.5″ deep! Pitch the hole .75″ right (for right handers) to make sure we don’t hit the thumb hole and we’re good to go!
The only thing I would recommend, is you start at 7/8″ diameter and gradually increase the size of the hole from there. The reason for this is to ensure we stay within the U.S.B.C.static weight limits.
I hope that clears up any confusion about the layout. Enjoy!