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Frequency Matching with a Meter

This article is the result of correspondence with Andy Boedecker in December 2004. I decided to turn the correspondence into an article because Jason Poston asked a pretty similar question later that same month. I figured it was worth doing this article once, rather than having to answer the question once a month.

The question comes up every month or so on various golf forums: "I just got a frequency meter. Now... how do I build a frequency-matched set of clubs with it?" Here's how I do it. It may be a little different from others, but it works for me.

Actually, the way I build clubs it's really two questions:

How do I build a club to a particular frequency?
How do I build a set of frequency-matched clubs?

Let's tackle both questions in that order.

Let's also keep in mind that this article does not deal with: How do I choose a frequency or frequency slope? That's a design issue. This article is limited to shop practice. It assumes you know the frequencies you want, and describes how to build the clubs to those frequencies.

1. How do I build a club to a particular frequency?

Let's say I'm building a single club, like a wedge, a fairway wood, or a driver. I'm not trying to match a bunch of clubs that I'm building at the same time, but rather match a single club to a specified frequency. (Yes, that specification is likely to have come from a need to match the clubs already in the golfer's bag. But, in the shop, the current question is "one club, one frequency".)

For building a club to a frequency, I use the clubhead itself as the "tip weight". I shim it onto the shaft so it doesn't wiggle around when vibrating in the frequency meter. There are a couple of ways to do the shim:

With a piece of monofilament fishing line. I wrap the line across the tip of the shaft and up the sides; then I press the head onto the shaft tip. (This tip is from Tom Flanagan.)
With a small strip cut from a plastic bag. I wrap the strip around the tip of the shaft, extending a little beyond the tip, and press the shaft into the hosel with a twisting motion. (This tip is from Paul Nickles.)

I prefer the former, mostly because it is less likely to leave a residue in the head that might interfere with epoxy bonding -- or at least have to be scraped away.

Before I go any futher, a few words about the frequency meter and measuring shimmed clubs in it:

No, I'm not going to call it a "frequency analyzer", even though most companies that make them advertise them that way. I'm an electrical engineer, and I know what a frequency analyzer really is. The companies are trying to make their equipment sound more sophisticated; but we all know that golf advertising is full of hype. Anyway, you put a shaft in and you get one reading out; it's a meter!
The butt clamp better be open in the back so you can extend the butt beyond the clamp. If it isn't, you can deep-six the rest of this article -- or deep-six your meter and get one with a decent clamp. (More on this in the Q&A below.)
When measuring the frequency of a shimmed head, don't try to orient the club in the "target plane" or heel-toe plane. Just let the clubhead hang the way it wants to (the Center-of-Gravity plane). That's because, unless the CG is aligned with the plane of vibration, slipping of the shim may occur and will result in a wrong reading; probably a low reading. If you are concerned about shaft alignment, twist the head so the shaft is aligned as you want to test, with the clubhead in the CG position.

Now get out your club ruler and mark off the length of the final club. (I use masking tape to mark it.) Clamp the club at that length and measure the frequency. At this point, the frequency is going to be lower than the target frequency. (It better be lower; tim trimming can only raise the frequency! If it's already higher, you bought the wrong shaft.) It is probably a long way from the target frequency if it's a fairway wood; it may be close if it's a driver.

I take a guess at a sensitivity, and compute a trial tip-trim that I know will be too small to get it to the target. Now I go through the basic sequence that is the heart of this procedure:

Tip-trim to the new trial point.
Re-prep the shaft, because I'll need more shaft exposed.
Re-shim the head to the shaft.
Re-measure the final length, and mark it. Lose the old mark. (That's why I use masking tape.)
Measure the new frequency, it should be higher than it was, but still no higher than the target.

Now I know the sensitivity, because I know how much I trimmed and how much the frequency changed. Knowing the sensitivity, I trim again -- but not to the full target frequency. I try to stop well short of it, because the sensitivity increases as you near the end of the parallel tip. You don't want to overshoot the target.

I repeat the basic sequence of steps above, getting closer to the target frequency, until I'm there. Usually requires three or four trim/measure cycles.

2. How do I build a set of frequency-matched clubs?

As you can see, this is a time-consuming process. If I'm building a set of clubs with the same model of shaft and a fixed interval of length and clubhead weight (like a set of irons), I take a short cut. It has never compromised the final quality of the set. Here's what I do:

I always work with a model of shaft whose consistency I trust. If I didn't, I'd have to completely match every club. But if I'm using shafts that are tightly matched in frequency and weight, I can get away with this beautifully. (BTW, the shafts that I find work so well are any model from SK Fiber or Mercury. Most steel shafts also work like this. I have been disappointed by most other graphite shafts, even high-priced ones. Of course, you can experiment and find others that work for you. Or, if you're patient and really have a thing for some inconsistent model of shaft, you can frequency trim each club using the other procedure. Or you can buy enough so you can select a set's worth of them with a tight distribution.)
I measure the frequency and weight of the shafts I got for the set. The frequency measurements are full-length, using a tip weight. You can use a standard 205-gram weight or any random 3/8" chuck. The important thing for this step is the relative ordering and spacing of the frequencies, not the absolute frequencies. I then sort the shafts in order of increasing frequency. For shafts of the same frequency, I break the tie in order of increasing weight. I don't use any shaft more than 3 grams off the median weight or 3cpm off the median frequency.
I mark the sorted shafts with their target club. I put the softest/lightest in the longest irons, and stiffer/heavier go in the shorter clubs.
I weigh the clubheads, and I add tip weights to the lighter ones so that the weight progression is 7 grams per club, within one gram. (This is for a swingweight-matched set. It's a little harder for MOI-matched.)
I pick one club to be the "pivot" or reference club of the set. Usually it's the 5-iron, but it doesn't have to be. I build that club to the target frequency, using the single-club approach described earlier. The difference is that I note the total tip-trim I used to get the target frequency, before I glue any heads on. (If I'm working with a familiar model of shaft, I may be able to skip this step entirely; I may know what tip trim I'm going to need without measuring.)
Then I tip-trim the rest of the shafts on the progression I want -- usually the same as the manufacturer's recommendation -- and cut and glue. This trimming is relative to the one I measured. An example is given in the following table:

Club	Manufacturer's recommended tip-trim	Tip-trim, based on 5-iron at 2 1/2" measured
1-iron	0"
2-iron	1/2"
3-iron	1"	1 1/2"
4-iron	1 1/2"	2"
5-iron	2"	2 1/2"
6-iron	2 1/2"	3"
7-iron	3"	3 1/2"
8-iron	3 1/2"	4"
9-iron	4"	4 1/2"

I now have an NF4, and my next few sets are going to be built to flex instead of frequency. Those who have used the NF2 report that their sets come out right on frequency when they're done, and the NF4 is even more accurate than the NF2. That should eliminate the trim/measure cycles down to just one measure/mark/trim.

Questions and Answers

Here are some questions that came out of correspondence on this subject, and the answers I would give:

Do you ever have shimmed heads come loose and fall off?
Do you measure frequency of a spined shaft with N1 at 9 o'clock, pointing at the target?
How can you align a shimmed head with the center of gravity in the vibration plane (as you recommend), and still measure the frequency of the shaft in the plane that you need to?
How can I simultaneously match swingweight and frequency?
What do I do about an old frequency meter with an inadequate clamp?
What specs do you give the customer?
Do you tape the shaft when you cut it, to protect from splintering?
What do you use to measure total club length?

Q - Do you ever have the shimmed heads come loose? I can see a $100 driver head flying off and hitting the concrete floor.

A - I've never had this problem. But it has occurred to me. One small precaution is to leave the plastic wrapper on the clubhead until the epoxy is cured. The wrapper will add a tiny amount of weight, but that will change the frequency by less than one cpm.

Q - It would also make sense to do these measurements with the shaft oriented the way it is going to be in the club, correct? For me, according to what makes most sense to me, that means N1 at 9 o'clock, pointing at the target, for the righty.

A - That's the "conventional wisdom". Makes no sense at all to me. Here's what I do.

First of all, you already know that I stick to shafts I trust (when I can pick the shaft). Those brands and models don't have spines big enough to be worth aligning; hell, it's usually hard even to find them. So I don't bother with alignment. And that's OK because the frequency will be the same no matter which direction you measure.

But if there is a significant spine, you really want to measure the frequency in the direction that the shaft will be doing the most bending. That's the heel-toe plane, not the face (target) plane. That's what I do if I have to use a shaft with a spine. I usually orient the shaft with the stiffest plane in the heel-toe direction, then build to the target frequency in that plane.

Q - If a shaft has a significant spine, wouldn't you need to twang it with the face pointed directly up or down with the FLO plane aligned with the target line? And doesn't that mean that you can't put the center of gravity of the shimmed head where you want, so you can avoid the head's slipping?

A - There are two assumptions built into the question, and I disagree with both.

You are assuming that the "interesting" plane to measure frequency is the plane perpendicular to the face. As I said in answering the previous question, I believe the interesting plane for frequency is the heel-toe plane.
You are assuming that you must have the head aligned to the shaft when you shim it, in the same orientation that you expect to build the club. Nothing could be further from the truth. The head can be in any orientation at all, and it will change neither the frequency nor the wobble due to the spine. The head is acting only as a tip weight at this point. The orientation that matters is that of the shaft to the clamp. So first set the shaft/clamp relationship as it needs to be for the spine, and clamp the shaft securely. Then turn the shimmed head on the shaft so the center of gravity of the head is in the plane of vibration for measuring the frequency.

Q - How do I simultaneously match swingweight and frequency? Before I got a frequency meter, I could just trim to the manufacturer's recommendation, then add weight as the swingweight scale tells me I need it. But won't that throw off the frequency?

A - Yes, it will throw off the frequency. Before you had the frequency meter, it also threw off the frequency; you just didn't worry about it. Now you have the means to measure it, so you know the frequency is off.

With the procedure given above for matching a set of irons, the swingweight or MOI is going to be pretty close. It will probably be within a swingweight point, and certainly be within two. It is a good rule of thumb that a swingweight change of one point (due to a change of either head weight or club length) will result in a frequency change of one cpm. So correcting a 2-point swingweight error could introduce a 2-cpm frequency error. (BTW, it might also be correcting a frequency error, but let's go with your assumption that it was right before you corrected the swingweight.)

So we need to decide which will affect performance more, a two swingweight point error or a two cpm error. Both are very small, but the swingweight is closer to the threshold of what the golfer will feel, or will be affected by. So correct the swingweight and let the frequency be a bit off.

Q - I have an older frequency meter where the clamping unit [is only 2" long, and has a stop at 5" which does not allow extending the butt.] What should I do?

A - I wouldn't trust a 2" clamping length to be rigid enough for consistent readings, and certainly not for anywhere near true readings. Get a new clamp! You can buy them from John Kaufman (Club Scout: http://www.csfa.com) or Ed Mitchell (Steelclub: http://www.mitchellgolf.com/). If you want to make your own, see the article on my web site describing my frequency meter. It includes lots of photos of my home-brew clamp.

Q - When determining final cpm measurements for the spec sheet you hand to your client, again, do you use the tip weight or the heads? I would think, once you are dealing with final club specs, due to different lengths, you need to start using the clubheads so the weight differences in the heads can offset the different lengths. Sound about right?

A - I keep the records. Most of my clients couldn't care less about the number. (Yes, some do; occasionally, I will give one a copy of the record.) The records I keep are of the finished club, cut to length, but without the grip. For most clubs, I also have the gripped measurements as well.

Recently, I also keep the trim/measure records for each club where I do trim/measure. Since I try to use the same models of shaft, this tells me a lot about sensitivity that I should be able to use in the future.

Q - Do you tape the shafts where you are making the cut? I have heard that this keeps the shafts from splintering.

A - I do if I'm cutting a graphite shaft by hand with a hacksaw. If I'm using a cutoff wheel or circular saw with abrasive blade, it probably isn't necessary.

It turns out this is a much more controversial topic than I thought. I once stepped into a fight between two clubmakers on this very question (just figuratively; it was on an Internet forum), and all hell broke loose for a few days.

Q - How do you measure total clublength? I use a simple 48" aluminum ruler that cost $9.00 from Lowes. I have seen devices that cost much more for doing this. Is something like the Accumade ($120) or True Measure ($45) worth it?

A - Any of these will do an effective job, though it's a lot harder to be effective with a simple ruler. It helps a lot to have a stop against which you can rest the sole of the club. My own solution is a fixed stop, rather than a hinged stop like the Accumade or True Measure. A stop that is fixed at 59° will give exact length for a club with a 59° lie -- obviously. However, it will also be within 1/8" of the correct length for lies between 54° and 64°, which is as close an any clubmaker needs to be on this measurement. Advantages:

Cost, obviously. You can build this yourself from a your 48" hardware store ruler. Just add an angled stop to the ruler.
Ease of use. You don't have to adjust the lie (and therefore don't have a chance for error) before you measure the length.

Last revised January 14, 2005