How to Match Shafts - 1

Dave Tutelman -- November 25, 2005


Matching a set of irons

The steps involved are:

Record stiffness of each raw shaft

Take a reading to measure the stiffness of each shaft, with the shaft tip against the tip stop as shown in the photo.

Record the reading, and be sure to have a way to associate the recorded reading with the specific shaft. That means that each shaft must have a unique marking. That marking cannot be the designated club (e.g.- "8-iron") -- at least not yet. We will assign shafts to clubs based on the stiffness we measure.

I usually put a letter (A, B, C, D, E,...) on the butt of each shaft, and pair the measurements with the letters.
In addition, I usually record the gram weight of each shaft. When sorting and assigning shafts, I use the weight as a secondary sort. That is, shafts with the same stiffness are placed in order of increasing weight. But, if the shaft weights are all within about 4 grams of each other, this is a pretty small effect and you can safely ignore it.

Here's an example of a table in which to keep your data. It is a snapshot of an Excel spreadsheet that does the calculations. You can download and use the spreadsheet to aid with your own shaft matching.



The spreadsheet as downloaded will be initialized with the same sample values as in this tutorial. Overwrite those values with what you measure.

Sort the shafts by their raw stiffness, and assign them to clubs

You now have the raw stiffness and perhaps weight of each shaft. Sort the shafts:
If you are using the Excel spreadsheet, here are the steps to do the sorting:
  • Using the cursor, select (highlight) the portion of the spreadsheet showing in the figure below. That would be the three columns "Label", "Weight", and "NF4 Raw Load". Highlight them for as many rows as you have data filled in, and be sure to include the header (title) cells.
  • Go to the "Data" menu and click on "Sort". That will bring up the Sort dialog box as shown.
  • Be sure the box says that there is a "Header Row".
  • Set the dialog box to sort first by "NF4 Raw Load" (ascending) and then by "Weight" (ascending).
  • Click "OK", and the table will be sorted.
Here's the table after sorting the shafts.

A couple of things to note here:
At this point, you can assign them to the irons you are going to build. Put the softest shafts in the longest clubs, and the stiffest in the shortest. Let's assign our sorted set of shafts to a "standard" irons set: 3-iron through pitching wedge.



So the 3-iron will be built from the shaft we labeled "G", the 7-iron from shaft "A", etc.

Find the tip trim sensitivity

We will measure the tip trim sensitivity of one of the shafts, and assume it is representative of all the shafts. This will be a good assumption for some models and not so good for others. But it won't matter, as far as the shaft matching is concerned. The only effect it will have is how quickly we zero in on that match.

Select a shaft that is most likely to be representative of the shafts being used. That is likely to be one of the middle rows of the table.

Place the shaft in the NF4, and repeat the former measurement (just as a check). Then slide the shaft so that 2" of tip is exposed beyond the previous measurement. See the photo, where the distance from the inside of the tip stop to the tip of the shaft is exactly 2". (If you are using millimeters instead of inches, expose 50mm of tip.)

Record that reading.

(There are ways of mounting a ruler to make it easier and faster to extend the tip a known amount. Here are a few...)

Now we have readings for a sample shaft at the tip and 2 inches up from the tip. The difference is the sensitivity, in kilograms of load, for a two-inch trimming of the tip. To get the tip trim sensitivity (TTS) in kilograms per inch, we divide the difference in load by the difference in trim (in this case, two inches). Mathematically, it is:
TTS = (Load2inches - LoadTip) / 2
On the spreadsheet, all you have to do is enter the two load readings (the green numbers), and it will compute the TTS for you.


Choose a baseline shaft and assign a load to it

To match the set of shafts, choose one shaft to which the other shafts will be matched. It is usually a good idea to start with the softest shaft (the one going in the longest club) as the baseline, since you can be relatively sure that it will be physically possible to get the right trim for all the clubs before you run out of shaft to trim. (If you started with a short club and worked backwards, the tip-trim for the longest club might turn out to be negative; you can't achieve the flex you need in order to match the set.)

Note that I said "relatively sure." If the raw shafts have some really large stiffness differences one to the next, you still might not be physically able to achieve your trim. But shafts with that big a mismatch are really poor quality. On this subject, I often order a few extra shafts so I can ignore "outliers" that seriously mismatch the others. But there are shaft manufacturers whose quality control is good enough that I don't have to do this if I order their shafts. One of the advantages of dealing with high-quality suppliers is that you don't need to over-order to be sure you have enough good shafts.

Note that the Excel spreadsheet requires the baseline shaft to be the softest shaft, which has been assigned to the longest club. If you choose another shaft for the baseline, you'll have to do some hand computation -- at least for the target load -- instead of just plugging things into the spreadsheet.

For our sample data set, we're going to use the 3-iron (shaft "G") as our baseline shaft, because it is the softest one we have. We will assign a target deflection to that shaft as trimmed. For this set, let's say we're going to leave the 3-iron untipped, so its target deflection will be exactly what we measured for the raw shaft: 5.30Kg.

Choose a target slope

In simple "cut and glue" clubmaking, the slope is determined by the shaft and the tip trim increment (such as a half inch per club). If you frequency match, then you trim to a frequency slope as measured by a frequency meter.

But we are matching with an NF4, so we need to express the slope in terms of NF4 load, not frequency. There are quite a few ways to approach this. For example:
Experience
 Once you have experience with the NF4 and the models of shafts you use all the time, you will have some "stock" slopes. You will pick the one you know will work, because you've done it before. (But, if you're that advanced, you're probably not reading these instructions. Just letting you know what you can look forward to.)
Manufacturer's
trim schedule
 You can go with the manufacturer's recommendations, and use the NF4 to enforce that the slope is followed smoothly and accurately. The manufacturer usually provides tip-trim instructions, recommending an increment something like 1/2" per club or 1/4" per club. Let's go through an example of this:
  • Suppose the manufacturer says to use 1/2" per club.
  • We know how much of a load difference our target shaft has with a 2" trim; it's the difference between the last two readings we took. Doing some arithmetic, we see that the difference was 0.63.
  • If a 2" trim gives a 0.63 load difference, then a 1/2" trim should give a quarter of that, a 0.16 load difference. So let's pick a target slope of 0.16 Kilograms per club.
Frequency
 You can take a frequency approach. Let's go through an example:
  • Suppose you want to build the clubs to a "Brunswick slope" of 4.3 cpm per club. Other references have shown that the shaft trim contributes about 2.5cpm to the slope, and length and head weight account for the rest. So we want a tip trim increment that contributes 2.5cpm per club.
  • If we know that a cpm is equivalent to X Kg of NF4 load, then we can convert that into an NF4 slope. For instance, suppose the mysterious X were 0.05 Kg. (We're still working on this, but we know it is between 0.03 and 0.06 Kg per cpm.) Let's do the conversion, assuming 0.05 Kg per cpm.
  • 2.5 cpm per club times 0.05 Kg per cpm gives a target slope of 0.125 Kilograms per club.

So now we have a target slope for the NF4 readings. For the remainder of our example, we will use 0.15 Kilograms per club as that slope.

If you are using the spreadsheet, enter this target load increment in the appropriate blue cell, and enter the baseline target load (from the previous section) in the other blue cell.

Compute a target stiffness for each shaft

The next step is to determine the stiffness (that is, the target load on the NeuFinder) that you want for each shaft. This is easy, because you have already chosen:
So all you have to do is space the loads from one club to the next by the amount of the target increment, starting at the baseline shaft. If you are using the spreadsheet, it has already done the calculations for you. The target load column is filled in with numbers starting with the baseline load of 5.30 for the 3-iron and going up by our target slope of 0.15 per club.



The Target Load is what you want to get from the NF4 after you have trimmed the shaft. That is the end goal of the whole matching procedure. You will find it by trial and error, which can get tedious. But the good news is: you can make a very good guess for the first trial point. So the number of trials it will take to find the trim will be very small. (In my first attempt at matching shafts using this procedure, six out of seven shafts matched the first trial -- no error. The other shaft had a small error, but matched on the second trial.)

In the next section, we will learn how to "guess" or estimate the tip trim, and use that estimate as the first trial point.

Estimate the tip trim

We already have the raw load and target load for each shaft, and a pretty good estimate of the tip trim sensitivity for the shaft. From these, we can calculate how much tip trim we should need. Later, we'll use this estimate as a starting point to measure the shaft for the actual trim point.

Computing the amount of tip trim we should need is pretty simple. We know:
So the formula for trim in inches is simply:
Trim = (TargetLoad - RawLoad) / (TTS)
If you're using the spreadsheet, you already have these numbers in the "Est Trim" column, as seen in the example below.



This should give the amount of tip trim we need. But remember, we didn't measure the actual TTS for each shaft. We measured one shaft and assumed they all have the same TTS. So we still have to measure each shaft to be sure we get the right target load when we trim. But now we have a very good place to start measuring: the estimated tip trim.

Use the NF4 to find the actual tip trim

We find the actual tip trim for each shaft as follows:
  1. Place the shaft in the NF4, with some tip extended beyond the tip stop. Initially, the tip should extend by the estimated trim for that shaft. For instance, for the 6-iron shaft in our example
  2. Measure the load on the shaft. Call that measured load "L".
  3. If L is the target load (or close enough to it, generally within 0.03Kg), then we are done. Mark the shaft at the left edge of the tip stop and trim it there.
  4. If L is not equal to the target load, release the tension on the shaft and slide it a little in the bearings:
  5. Return to step #2 and continue.
How effective is the estimation? In order to test the matching procedure, I went through it with eight original Balistik shafts. I used the spreadsheet to estimate the tip trim from the measurements. Then I found the actual trim points, starting from the estimated points. The estimates were very effective. Of the eight shafts:
Even so, do not just trim to the spreadsheet's recommendation without checking the load, especially if you must trim considerably more than 2". I went through the procedure again with the same Balistik shafts, but with a larger initial trim. This is realistic because the Balistik is a combo shaft. You can get any flex out of it from a soft A-flex to an S-flex, simply by varying where you start your trim. In this case, my trims were between 3.5" and 6", but my estimate of Tip Trim Sensitivity was based on trims less than 2". Since the TTS can vary -- on most shafts, the TTS increases as you trim closer to the end of the parallel section -- the Estimated Tip Trim column is likely to recommend too much trim. In this case, the recommendation was between 1/4" and 5/8" too much. It took at least two and usually three iterations to find the correct trim.

So by all means do check the load with the NF4 before you actually trim the shaft.



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Last modified by DaveT - 12/27/2005