Greetings, when we get a new shaft in the 1st thing we do is spec it out.
For us, that means weighing it, measuring the tip and butt diameters, checking the length of the parallel tip section and in some cases measuring the torque and profile.
We also check what we call the build range. In our California Custom Fitting Studio we fit people to an exact and specific frequency at a given length, not just stiff or regular, but exactly how stiff or regular.Frequency is a digital way to measure a shafts stiffness and it is the basis for the number system assigned to Rifle shafts.Rifle shafts come as 4.5, 5.0, 5.5 etc.The higher the # is the stiffer the shaft. It is a much more precise way to measure flex, as you could have 2 shafts or clubs that say regular flex, but when you actually measure them, find they are no where near the same stiffness. So when some one says regular flex the question becomes, how regular?Do you want a softer regular more in the direction of a senior flex, or a harder regular more in the direction of a stiff?
The protocols we use to derive the numbers when we list the build range of a particular shaft are as follows.
For wood shafts we take a 200 gram driver and mount it, then measure out to 45” playing length and put a grip on there, we them clamp it in a 5” clamp and take a frequency reading.By our methodology 250 cycles per minute at 45” gripped in a 5” clamp equals a 5.0 build, 245 would equal a 4.5 build and 260 would equal a 6.0 build.
Now, let’s say the raw shaft is 46” long as most of them are, and it has a 3” parallel tip section, and it has an insertion depth of 1 3/8” in the head.We know that we can trim up to an additional 1 5/8” from the tip before we run out of parallel tip.
We also know that most shafts have a tip trimming sensitivity of near 6 cpm’s per inch.So if that driver started out at 250 cpm’s or a 5.0 as we are calling it with no tip trimming and we were to trim the maximum, 1 5/8 from the tip we would raise that stiffness reading near 10 cycles from 250 to 260, or from a 5.0 to a 6.0.So in this case we would say that this shaft has a build range of 5.0 to 6.0.
The longer the parallel tip section is on a given shaft the broader its build range is going to be.For irons we use a 243 gram 3 iron and measure out to a 39” playing length. At this length we would call 303 cpm’s a 5.0, and 298 cpms a 4.5, and 313 cpms a 6.0.
For Hybrids we use a 230 gram 2 hybrid and measure out to a 40 ½” playing length. At this length we are calling 290 cpms a 5.0, ten more cycles would be a 6.0 and 10 less would be a 4.0.
Here is a picture of the chart, but what's missing is our clear over lay showing how the freq #'s must increase as the club gets shorter to maintain the same stiffness.
Its sort of like if you had a bamboo pole 20 feet long and were holding one end of it, it would feel pretty flexi, but if you started walking hand over hand down the length of the pole it would feel stiffer as it got shorter, but it really isn't, it's the same pole, but because the beam length is less, it doesn't flex as much.
If you look at the chart below and you go to the top left, that would be a club that was 47" long and had a frequency of 275 cpm’s that would equate to a build of near 9.0 on my clear overlay.If you followed the top of the chart going to the right until you get to the 45" length you will see that the freq # there is near 290, so as the clubs get shorter they must measure stiffer to maintain that 9.0 build.