The Mysteries of Spineing Explained

After spineing my new Dynamic Gold X100s today I began to wonder why steel shafts had spines? (Apart from my own irons it is very rare for me to work on them.) I was surprised at the 'strength' of the spines. I came across this internet article on spineing generally. It is the best I've read, so thought that I'd share it:

http://www.tutelman.com/golf/shafts/allAboutSpines6.php

Interesting article Ivan, but please indulge me in the spouting of my analysis of the article and spineing in general (it occurs to me that maybe I should write a more detailed article on the subject - maybe if I can get time).

The article, although interesting enough falls into the usual analysis to prove that through empirical testing the theory is proven, unfortunately to me it doesn't really do any such thing.

The problem I have is that in the real world everything works in 3D, simple 2D analysis does not work. Basically what you are trying to find when spineing is the relative stiffness of a tube when flexed in terms of cycles per minute, the resonant frequency of the shaft. This is, as the article correctly states varies because of the way the shaft is built up. This is illustrated by the cross-section of the shaft showing the overlaps in a steel shaft from which you can conclude that obviously the thicker the overall wall the stiffer the shaft in that axis (this is quite easily calculated, it's known as the second moment of area, with the rather confusing units of mm^4). Unfortunately shafts aren't actually built parallel so the spine will vary and spiral along the length of the shaft, even worse if there are steps. A simple way of showing this effect is to wrap a sheet of paper into a tube - the spine (overlap) is easy to see. Now try doing it so the tube is tapered, the seam is a bit more complex and so is the overlap. So what is actually happening when a shaft is spined is that at best you are getting an average line which ignores any torque effect that will also vary the spine.

And just to throw a final spanner in the works it's all very well finding the natural resonant frequency of the bare shaft and then you go and fit an enormous offset weight of the thin end and a massive rubber damper on the other....

Tim,

The issue as I see it (from a layman's point of view) is not how the spine affects stiffness rating but how it affects torque, i.e. shaft twist. Just looking at the c.p.m. differential would suggest that spineing a shaft would have absolutely no significance or very little. Three things suggest to me that this is far from being the case:

(1) Turning the shaft under just a few pounds of pressure in a free rotating tube causes a very significant 'snap' in the shaft as it clicks into its neutral position. I can only guess what weight it would take to create such a yank - at least 16 ozs. I guess. Of course it varies from shaft to shaft and there's always one shaft in every fifteen or so shafts where one struggles to find a spine at all. (Have you felt this Tim?) So how is such influential?

Without being engineering qualified all I can do is provide an analogy:

(2) The wheels on my old car were adequately balanced. However they were rusting metal wheels so I removed them from the vehicle and painted them. Now most everyone knows how heavy a car wheel, fitted, with a tyre is.

Simply sanding off the rust and replacing such with paint will not have created (in weight terms) any significant difference.

However, because the wheel spins the (likely) almost imperceptible difference has 'multiplied' (for want of a scientific term) and now causes the steering wheel to shake.

As this analogy will almost certainly be shot down in flames as being unrelated and void I will make a final point.

(3) I have widely tested driver shafts in several sorts of situations.

(a) By orienting a heavy spine to target I have increased c.p.m. by as much as 9. I personally have not noticed any stiffness difference where the reading is under 7. But this is not what we are discussing.

(b) Once when I was been driving really well I actually compared two identical as possible drivers for accuracy. The properly spine aligned shaft was significantly more accurate than the shaft which I had severely mis-aligned. I used identical balls (but marked differently) and hit forty balls in session one (5 balls with one driver and then 5 with the other). After a ten minute break I repeated the exercise. The mis-aligned driver definitely had a tendency to splay balls right of target.

In the final analysis Tim I can't argue engineering with an expert Engineer. All I can due is advise as to the result of my empirical findings. Any thoughts I have on how my results happened (eg. the car wheel) are no more than clumsy schoolboy attempts to rationalise what I find. And very likely daft.

But with the greatest respect Tim (and I mean that most sincerely as Hughie Green used to say, and I do) I will always choose my test results over engineering theory. Engineering 'fact' has a strange way of being affected by other engineering facts during the course of the golf swing and possibly producing unexpected results.

I don't doubt what you say Tim, save only that, for a skilled player, spineing makes a very significant difference to driving accuracy. It won't be so influential with irons because of a number of factors principally swing speed.

Would never be offended by your comments Ivan, you should know that by now! I don't doubt that you can feel the difference which is why I always feel slightly uncomfortable with a slightly cod-science analysis in the article, I've been an engineer for longer than I've been a golfer and my approach has always been to calculate then test. Having said that what I would like to see (related to a point I've mentioned to you a few times) is a comparison between shafts that are wound (even steel shafts) in the opposite direction to see whether or not that would have a negative impact. I've always ascertained that graphite shafts could be made better by having additional helical winds to favour left or right handed players and I don't see why it shouldn't be the case with steel. Maybe I should nip over and trying an extra winding of, say, Kevlar on one of your shafts. Be an interesting experiment.

PS The wheel thing is easy. You may have only changed the static balance of the wheel by a small amount, but the out of balance force will be multiplied by the square of the rotational speed - so a small mass will have a large effect. You are then assuming after cleaning and painting you then replacing the wheel in exactly the same place, with the same nuts all transmitting the same force to the hub as before. Add to this the natural OOB compensation that the other parts of the wheel assembly tend to pick up and the margin for error increases. Either that or your car is a pile of cr*p.

Tim,

With regard to graphite shafts nowadays I only personally use seven part 'bamboo' shafts which return around 14% more energy than tubular shafts. They hit far longer. I am told that their accuracy is also unsurpassed but I do not have the ability to test that.

I don't own a car as such, but rather a compromise. Nevertheless she is reliable. I did own a vehicle but alas destroyed her through my engineering. I changed an oil filter; accidentally left the old rubber ring in situ; effectively fitted my new filter with two seals; lost oil and my engine seised. At least that is what I was told at the time. The garage took my scrap and paid me with Ethel, my compromise. I later learned that the garage repaired her with a mere £850. worth of parts.

I try to do everything myself in life to avoid being duped, but sometimes it costs me due to the errors of a virgin. But even after writing off my car via bad engineering the ten grand lost is nothing compared to what I have saved over the years.

You were coming over to see me years ago, when I lived in your country. You were then I believe still in short trousers. Let's make it happen one day - but hopefully to play golf rather than play science. Present golf science is largely primitive and irrelevant. We are in the early innocent days. Example, fixing the C.O.R. of driver faces at a maximum 0.830 based on engineers having a driver head delivered to a steel ball at 110 m.p.h. Few golfers can swing at 110 m.p.h. and no-one plays with steel golf balls. Example, adjustable drivers don't work. Example, bigger driver heads are better. They are patently worse. Engineering golf and real golf are light years apart.

My rebuilt irons will be ready tomorrow, two full days of work and three new wedges. I had to have them as all my old excuses for playing badly have long worn out. The amusing thing is that they have been carefully prepared to slow down my swing and massively reduce my hitting distance. In science terms - making a car run on two cylinders. Sometimes one just has to put two fingers up at science and do the opposite to what engineers strive for.

All that can be relied on is the sun coming up in the morning, and that tends to only last for every five million years or so until Mother earth stretches and tilts her axis.