Butt Frequency and Tip Stiffness Are Two Different Conversations

Bench note 04 · Frequency · About six minutes

Clamp a finished club at the grip end, pull the head down, let go, and count how many times it oscillates in a minute. That figure is butt frequency, quoted in cycles per minute, and it is a genuinely excellent measurement. It captures shaft stiffness, playing length, and head mass in one reading, which means it describes the assembled object rather than one of its parts.

What it does not do is tell you how the last eight inches of that shaft behave.

Why the Clamp Position Matters So Much

The test holds the butt rigid and lets everything below it move. The sections nearest the clamp contribute most to what you measure, because that is where the bending moment is largest. The tip section is at the far end of a long lever and its individual contribution to the reading is comparatively small.

This is not a flaw in the test. It is what the test is for. But it produces a consequence that surprises people the first time they see it demonstrated on a bench.

Two clubs can read within one CPM of each other and produce visibly different ball flights, because the number never described the part of the shaft that was different.

A Concrete Case From the Bench

A customer brought in a driver built by someone else and asked why it launched lower than a club he had previously owned, given both were the same length and, according to a frequency reading someone had taken, the same stiffness.

They were the same at the butt. On the profile board the two shafts diverged sharply from about the midpoint down: one had a soft, progressive tip and the other firmed up hard in the last six inches. Those two shafts will never produce the same launch condition, and no frequency reading taken at the grip would ever have shown it.

So What Is Frequency Good For?

A great deal, provided it is used for the job it does well.

Matching clubs within a set

When every club in a set uses the same shaft model, the tip behaviour is a constant, and frequency becomes an excellent way to confirm that the set steps evenly. This is the single most valuable use of the machine and it is why we plan a frequency slope before cutting anything.

Verifying a build against its spec

Once a target is written on the build sheet, frequency is how we prove the finished club hit it. Our tolerance is one CPM either side, checked after the epoxy has fully cured and the grip is on.

Detecting that something has changed

A club that reads eight CPM different from where it was built has something wrong with it — a loose head, a shaft that has been shortened, a grip change, or a replacement nobody recorded. It is a diagnostic, not just a specification.

What to Use Instead for the Tip

Tip behaviour is read from a profile scan on the raw shaft, before installation, at stations along the length. That is a different instrument answering a different question, and there is no shortcut that turns one measurement into the other.

In practice we use both, in a fixed order. Profile scan to choose the component. Frequency to plan and then verify the assembly. Anyone offering to specify a shaft from a frequency number alone is describing the club they already have, not the one you should be playing.

Summary for the Impatient

• Butt CPM measures the assembled club, weighted heavily toward the grip end
• It is the right tool for matching a set and verifying a build against spec
• It is the wrong tool for comparing two different shaft models against each other
• Tip section behaviour requires a profile scan, taken before the shaft is cut
• Both numbers belong on the build card, because each answers a question the other cannot