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Drilling Top Weight / CG Position Blems with Powerhouse Blueprint

Date Posted: December 3, 2011

Category: Blueprint Tutorials

A very common topic in the bowling internet forums is the drilling of bowling balls with unique undrilled static imbalances.  This includes balls with unusually high or low top weights, unusually long or short pin-to-CG distances, and unusual center of gravity (CG) locations (such as those that are not located along the line from the pin to the mass bias locator), all caused by natural manufacturing process variation.  These conditions are usually found on discounted "blems" or "x-out" balls, often purchased online by bowlers looking for a good deal.  This article will explore the ways in which Powerhouse Blueprint can make the drilling of such balls much easier on the pro shop operator.


Before we begin, we'd like to establish a few definitions regarding an undrilled ball's static imbalance so that there is no confusion going forward.  First off, most bowling ball manufacturers specify two parameters on the ball's box relating to undrilled static imbalance:

  • Pin-out distance:  This is the distance of the CG mark to the pin.  This is often listed as a range of distances, such as 2"-3" or 4"-5".
  • Top weight:  This is the magnitude of the static imbalance, usually listed in ounces.

For asymmetrical bowling balls, there is a third parameter that is necessary to describe the undrilled static imbalance, and that is the location of the CG relative to the pin / mass bias marker line.  This is often not listed on the ball's box, but must instead be measured on the ball itself.

For the purposes of this article, we will use the nomenclature of Powerhouse Blueprint in describing undrilled static imbalance of asymmetrical balls, as shown in the below image:

Powerhouse Blueprint undrilled bowling ball static imbalance

So then, the third parameter to describe the location of the CG is the angle between two lines:  1) the line from the pin to the mass bias marker, and 2) the line from the CG to the pin.  The angle is expressed in degrees from -180 to 180, using the sign convention shown above.  In this article, we'll refer to this angle as the "MB-to-pin-to-CG angle", or, more simply, just the "CG angle."

Potential Challenges Encountered When Drilling Static Imbalance Blems

A lot can go wrong when drilling blems.  Three main concerns of ball drillers are listed below:

  • Legality of as-drilled static weights:  As we all know, all drilled bowling balls must meet the top/bottom weight, side weight, and finger/thumb weight requirements of the appropriate governing body (the USBC, for example).  With blems, the tendency is to be extremely conservative with the layout used in order to be certain that the static weights will be legal once the ball is drilled.
  • Normal track flare vs. reversed track flare Reversing of track flare / flaring over a hole:  When drilling blems, it isn't unusual to use pin and mass bias placements that stray from a ball driller's comfort zone, leading to concerns that the drilled ball will flare over one of the ball's holes when thrown (which is an extremely undesirable condition).  An example of a ball with reversed track flare is shown to the right in the bottom image.  This ball will roll over the middle finger hole during the last eight revolutions.  Clearly, the down-lane bouncing caused by this will have a very bad impact on the ball's reaction.
  • Undesired on-lane ball reaction:  In large part, the change in ball reaction that a ball driller can impart through the choice of drill pattern and balance hole position is caused by the resulting change in the flare characteristics of the ball.  This is due to the potential of track flare to significantly change the amount of friction experienced between the coverstock and lane when thrown, which is a function of the degree to which the track flare rings overlap (generally speaking, tighter track flare ring spacing results in lower friction and wider track flare ring spacing results in higher friction...however, there is a point of diminishing return as flare ring separation goes beyond a certain value).  Since, as already stated above, blems often require unconventional drillings that stray significantly from well-understood drillings, it is entirely possible (and common) that a ball driller could intend to drill a ball to flare very little, but accidently end up with a ball that flares a lot (or vice-versa).

Now, with these potential problems in mind, let's take a look at how Powerhouse Blueprint can help.  We'll first outline a very high-level process and then we'll look at a specific example.

Blueprint Ball Drilling Process Overview

What follows is a general process to follow for best results when drilling bowling balls in Powerhouse Blueprint.  This process applies to blems as well as non-blems:

  1. Weigh and the undrilled bowling ball on an accurate (and calibrated) static imbalance measurement device to determine its actual CG location and top weight.  While the manufacturer's CG mark and supplied top weight value are generally reliable, it doesn't hurt to measure (and remark, if necessary) the ball yourself so that you don't run into any unpleasant surprises after you've drilled the ball.
  2. Measure the pin-out distance and CG angle. This can be done quite easily using standard pro shop measurement tools, such as the Pro Sect™.
  3. Blueprint's undrilled CG input dialog box In Powerhouse Blueprint, load the appropriate bowling ball from the ball library and then perform the core shifting operation to give the "virtual" ball the same static imbalance as the actual ball to be drilled.  This is done by clicking Ball Operations => Shift Core from the main menu or by clicking the corresponding toolbar button.  For example, if the ball you are drilling has 5 ounces of top weight, a 5 inch pin-out distance, and a -40 degree CG angle, you would enter these values as shown to the right.
  4. Virtually drill the ball using Blueprint however you like, modifying the various drilling parameters (including balance hole position, size, and pitch) to achieve the desired result.  At this point of the process "desired result" simply means that you drill the ball such that it is statically legal and that the positive axis point (PAP) is placed in a location relative to the min and max RG axes such that the ball's track flare will be close to what you want to see on-lane (pin / mass bias placement relative to PAP, RG contours, etc. will be covered in-depth in a future post, so we apologize if this description is a bit vague right now).  To continue our example, suppose we want to drill this ball to flare very little.  To do this, we'll attempt to position the PAP so that it is far (approximately 6 inches) from the min RG axis and close (approximately 1 inch) to the max RG axis.  In this case, we've achieved this goal with a drilling that places the pin 6 1/8 inches from the PAP with a 10 degree MB-to-Pin-to-PAP Angle and a 30 degree Pin-to-PAP-to-VAL angle (commonly referred to as a 10 x 6 1/8 x 30 drilling), with a large (1 inch diameter and 3 inch depth) balance hole on the PAP, pitched 2 inches horizontally away from grip center.  This is shown in the image above.
  5. Virtually throw the ball in Blueprint to see if it flares as desired.  At this step, it is critical that we make sure the ball is not flaring over any of the holes.  As shown to the right, our track flare in the above example looks to be exactly as we've desired.  If, alternatively, we had chosen a drilling that resulted in an undesirable flare pattern, we could easily return to Step 4 above and make the necessary adjustments.
Other Possible Drillings for the Example Ball

To illustrate the power of Blueprint's virtual ball drilling and on-lane motion simulation capabilities, we'll now continue the above example and show a variety of drilling configurations that could be used to achieve different on-lane reactions.  To be clear, please keep in mind that these are not drilling recommendations that we think people should be using; rather, these are just random examples of ways in which this particular ball could be drilled to illustrate the point that your options regarding the drilling of blems aren't necessarily as limited as you might think they are at first glance.

Here are two possible drilling options...

Example drilling layouts

...and, here are two more, all four of which are legal with respect to static imbalance.

Example drilling layouts

In terms of on-lane reaction, the drillings shown above result in a total hook variation of about 5 boards, largely due to the changes in the track flare of the ball:

Blueprint ball path predictions

Tips and Recommendations

We'll close this post by providing a couple of tips that you should keep in mind when using Blueprint for simulated ball drilling (particularly in cases like those shown here involving blems):

  • Accurate bowler delivery input is critical.  Make sure that you know a bowler's PAP, ball speed, rev rate, axis tilt angle, and axis rotation angle before attempting to use Blueprint for anything like what has been shown in this post.  Small errors in any of the input parameters can result in a drilled bowling ball that isn't going to perform as predicted.
  • Blueprint is not a replacement for actually checking the as-drilled static weights on the scale.  The static weights in Blueprint will track pretty closely with the actual static weights measured on the scale, but there will be slight differences.
  • Because Blueprint can't perfectly predict static weights, try to leave yourself an "out" when you have predicted static weights that are close to the legal limits.  What we mean by this is that you should always, when possible, have a plan for what you can do to fix a ball that has already been drilled, but checks slightly illegal on the scale.  For example, if Blueprint predicts 0.90 ounces of finger weight, make sure that you have some room to increase the finger hole depths in the event that the static weight scale shows the drilled ball to have 1.10 ounces of finger weight, for example.  You can, in many cases, employ the same strategy with balance hole depths.  Leaving yourself an out post-drilling can save you a lot of trouble and we highly recommend it, when possible.
  • Don't "push your luck" too far.  For example, try not to drill a ball that comes within 1/64" of hitting one of the holes in the Blueprint simulation.  Why?  Your bowler delivery parameters are not perfectly accurate, the mass properties of the real ball aren't 100% accurate due to manufacturing process variation, and the bowler will have natural variation in release consistency.  For these reasons, a ball that doesn't hit any holes in Blueprint may occasionally (or frequently) hit a hole in real life if you haven't left yourself enough of a "buffer" to allow for these variations.  For an average bowler that has never been Blueprinted by you before, we would recommend that you try to maintain a 1 inch buffer between the closest track flare line and hole edge.  For elite bowlers (with consistent releases) and those that you have a lot of experience with, you can relax this requirement slightly.

We hope this post has been informative, helpful, and useful to you in getting the most out of Powerhouse Blueprint.  In a future post, we'll share with you some additional information about using Blueprint to squeeze that last 10-20% of performance out of a ball using some (as far as we know) previously unused drilling methods.