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Frequency Matching Graphite Iron Shafts

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Sorting By Frequency

Now it is time to take a set of nine different iron shafts and begin the matching process. The chart below lists nine assumed shafts and their frequencies. Frequency should be obtained by using a 235 gram weight because it is the most popular 2 iron head weight available in the component industry. Notice that each frequency is matched with an iron (2 iron through PW)

The matching process is very straight forward. First, take the lowest frequency shaft (in this case, 284 CPMs) and mark it your 2 iron. Then, take the next highest frequency (285 CPMs) and mark it your 3 iron. Continue this process until all of your shafts are numbered. After you complete this process, you should make sure the frequency and iron number are clearly marked on each shaft for future identification.

Adjusting for Weight Discrepancy

Before you can actually frequency match the shafts, you must account for how the iron head weights will affect your club frequency. The chart below describes exactly how to do this.

The chart lists the "DESIRED" and "ACTUAL" weights for a sample set of nine iron heads (column 1 & 2). In order to determine how weight will affect your frequencies, you must first determine the gram variances (A-B) between the actual and desired weights of the heads.

If an iron's actual weight is below the desired amount, you need to add a weight pin to make up the difference. If an iron's actual weight is over the desired amount, you must determine how much this weight overage (Column C) will reduce shaft frequency.

The Weight/CPM chart shows how weight overage equates to reduction of CPMs. The Weight/CPM chart is obtained by frequency testing a representative iron shaft at 235 g, 237 g, 239 g, and 241 g to determine the respective reduction in CPMs for increased weight.

The information shown in the Weight/CPM chart is only an assumption. Please keep in mind this chart will change for every model and every flex of shaft. After you have obtained your weight overage, you can use this Weight/CPM conversion chart to decide the overage differences in terms of CPMs. The desired weights listed in column A of the Weight Conversion chart were chosen after reviewing numerous component providers' specifications and noting that these were the most widely accepted weights. The seven gram increment between each iron head also seems to be an industry standard. Based on the Weight/CPM chart, we know that for every seven gram weight increase, the shaft frequency will be reduced by roughly 5 CPMs. Notice that the Standard Weight increment listed in column D increase by 5 CPMs for every 7 gram increase in iron weight shown in column A.

Now, take the overage figures in column C and add them to the CPMs in column D. You now have the Total Overage and Weight Difference figures necessary to match you set of irons.

Deriving Total CPM Adjustment

The next step is to take your nine shafts, each marked with a frequency and an iron number, and place them in ascending order (see figure 5 column A). Once you have done this you need to decide what the desired frequency for each shaft is. (Figure 5 lists the desired frequency for a set of random R flex shafts). Your desired frequency will always depend on how stiff you want the shafts to be.

After determing the CPM difference between the desired frequency and the frequency obtained using a 235 g weight, you must now factor in the Total Overage and Weight Difference figures from the last column of Figure 4. You will notice from the chart the various CPM differences between the raw and desired frequencies. There are also CPM variations derived from the Total Overage and Weight Difference. Add these two figures together (C+D) to determine how much you need to tip trim each shaft.

Figure 5: Tip Trim Chart

IRON	Natural Frequency CPMs) A	Desired Frequency (CPMs) B	CPM Difference C (A-B)	Total Overage and Weight Difference Taken from fig. 4 D	Total CPM Adjustment (C+D)	Tip Trim Amount (inches)
2	284	289	5	0	5	---
3	285	293	8	7	15	---
4	286	297	11	10	21	---
5	288	301	13	18	31	---
6	290	305	15	21	36	---
7	293	309	16	25	41	---
8	294	313	19	30	49	---
9	296	317	21	39	60	---
PW	299	321	22	40	62	---

Deciding Tip Trim Amount

To determine how much tip trimming is necessary to obtain the desired frequency for each shaft, you do not need to tip trim small increments to acheive the desired frequency. Instead, you can push the shaft in the frequency analyzer toward the direction of the tip while keeping the position of the tip weight constant.

By doing this you will be able to see the frequency of a simulated, tip trimmed shaft. If the frequency is what you desire, mark the position of the tip that extends beyond the leading edge of the tip weight and trim it off with a circular saw. Upon completing the tipping process, you can now butt cut each frequency matched shaft to their respective length.

Remember, the tip trim charts describes a random set of shafts and does not intend to give proper tipping amounts or desired frequencies for your set of shafts. Because every shaft model and every shaft flex is different, you need to determine the proper tipping amounts for every shaft model that you use.

As a result, you need to take your own set of shafts and iron heads, measure their frequencies and weight, determine tipping amounts, and decide on desired frequencies and weight, determine tipping amounts, and decide on desired frequencies in order to match your set. However, by carefully following the above process with your shafts and iron heads, you should end up with a frequency matched set.

While frequency matching is an effective way of building a set of clubs, it is not the only way to determine flex. Harrison has always provided clubmakers with tipping instructions based on shaft flex. These instructions, based on flexes defined by a static deflection board, continue to be supported by the great majority of shaft manufactureres worldwide.

Finally, whether flex is determined by frequency or static deflection, it is very important to remember that flex is only one of many important shaft specifications. As a club builder, you know that all golfers should be matched with the correct torque, weight, flex point, and length. While determining the correct flex for a player is important, it means very little if the other specifications are ignored or minimized.