Moment of Inertia (MOI)

Equipment
41

Lag,

To answer one of your questions, at least from the mathematical point of view, the location of the tape absolutely matters. MOI increases as the square of the distance the mass is located from the axis around which the MOI is measured. So, yes, I am positive that Richie wil be able to see the difference when locating tape behind the sweet-spot or around the hosel

Richie,

Have you ever considered matching clubs for others as a service? What I mean really is just doing the final trim with lead tape. The reason I ask, I built a set of irons that were MOI matched using a fairly simple formula. I weighed each head and shaft and calculated an MOI assuming 1 cm length gaps. I trimmed them to about +/- 2 kg*cm2 using hosel weights. It turned out really well in terms of on-course performance. I broke 80 three times in the last two months using these clubs. That matches the number of times I have broken 80 in my life up to that point. Now I have to admit that hard drilling on module 2 has had an effect too. I am using my legs in the swing for the first time in my life.

The only other method I can use to measure the MOI is to swing them like a pendulum and measure the period of oscillation and calculate an MOI. It turnes out that measuring this period accurately is hard. To do this well, the period needs to be measured to better than one part in 3000. That is tough with a stopwatch and a twitchy thumb. I have considered building a laser/photodiode combination to take the human out of the equation, or maybe use video … but that is more work than I had the time for at the moment. And, it is hard to swing the club, without friction, and not have it wobble out of plane.

For those that are interested in details, I used this formula
MOI = L*L(s/3 + h + w)
Where L is the finished length of the club, s is the weight of the shaft after trimming, h is the weight of the head, and w is the hosel weight used to trim the club to a good MOI. I ignored the sand wedge.
The set I built turned out like this.

Club | L(cm) | h(g) | s(g) | w(g) | MOI(kgcmcm)
3 | 98 | 242 | 127 | 1 | 2716
4 | 97 | 250 | 124 | 0 | 2714
5 | 96 | 257 | 123 | 0 | 2717
6 | 95 | 262 | 124 | 1 | 2714
7 | 94 | 268 | 127 | 1 | 2715
8 | 93 | 275 | 125 | 1.5 | 2713
9 | 92 | 281 | 126 | 2.5 | 2714
w | 91 | 288 | 127 | 3 | 2716
s | 90 | 301 | 124 | 0 | 2727
(I have no idea why I cannot space this table properly. the shaft weight, s, listed is the before trimming weight. To find the trimmed weight used in the moi forumula, multiply by trimmed length and divide by 41 inch raw shaft length.)

Now, you can see immeadiately the approximations made here.
This formula assumes that the shaft is as long as the finished club (ignores the fact that we don’t have a bore-through head.)
This also estimates the clubhead as a point mass located at the end of the shaft. (ignores hosel length, blade length, etc.)
This also assumes that the added weight is located at the end of the shaft.
None of these are horrible as approximations. But, I would not expect these calculations to be match the real club to 1/3000.
That is why I think that the blueprinting process I show above should be followed by a lead tape tuning process using a device that measures the final MOI.

But, I can say that my first experiment with MOI matching suited me very well. This is the first set of irons that I have ever had that I felt confident with every club in the bag. With these same heads and shafts trimmed to 1/2 inch increments and swingweighted to a constant swingweight, I have never hit the 4-iron well. I have always loved the 7 and 8 irons, but I have previously kicked this 4-iron head out of the bag in favor of a hybrid. Now, I love this club. I love punching out of trees with it. I enjoy full swings with it. It feels like a whole new club to me.

Oh, and Saturday, I had the chance to play a quick 9 holes. I hit 8 greens. We won’t talk about my putting. Now, I have to give some credit again to module 2. But I don’t think i have ever hit 8/9 greens before in my life. As a next step, I would like to make a heavier set. These have dynamic gold R300s in them. I bought these before starting ABS, so I would like to try a heavier and stiffer shaft. And, I would really like to find a set of heavy heads like some Macgregor M85 wingbacks or colokroms. If anyone has a set of these heads laying around … :slight_smile:

42

R3 J
can u plz post the total weight/length of those clubs.

43

Here’s what I have so far:

Driver (Wishon): 45.0" long, 2,830 MOI, D-3 swingweight, 323 grams
3-wood (Wishon): 43.0" long, 2,795 MOI, D-4 swingweight, 344 grams
Hybrid (Mizuno): 40.5" long, 2,766 MOI, D-4 swingweight, 369 grams

3-iron: 39.5" long, 2,725 MOI, D-3, 415 grams
4-iron: 39.0" long, 2,725 MOI, D-3, 417 grams
5-iron: 38.5" long, 2,725 MOI, D-5
6-iron: 38.0" long, 2,725 MOI, D-6
7-iron: 37.5" long, 2,725 MOI, D-6
8-iron: 37.0" long, 2,728 MOI, D-6
9-iron: 36.5" long, 2,725 MOI, D-7
PW: 36.25" long, 2,725 MOI, D-8, 457 grams
SW: 35.75" long, 2,725 MOI, D-9, 475 grams
LW: 35.5" long, 2,725 MOI, D-9, 477 grams

Right now I’m installing the hosel weights, so I’m removing the shaft, installing the weights and then reinstalling the shafts. I think there’s an easier way. But, that’s why I don’t have the full weight of the 5-iron thru 9-iron at the moment.

3JACK

44

Thanks Richie
I did manage to achieve progressive swing weighting on Mac VIPs mainly by inserting hosel weights, and was able to save the original ferrules with the serial numbers. I will post them tomorrow cos the hospital computer is not allowing me to access Skydrive. The swing weights are very simillar to yours but my total weights are much higher.
While you have the components can you apply the formula qouted by NRG (MOI= Length² x (Head weight + Shaft weight/3) and see if it comes close to the numbers from the machine. I did it with the 9 iron with a head weight of 295 g and the numbers come to be 4442 considering the shaft weight of 125 G and 4452 considering shaft plus grip weight of 175G.

45

Yes, that is the formula to use for MOI matching, although I’ve been told that its margin for error is greater than using the machine. However, I think your math is wrong. I believe you would be in the 2,600 to 2,900 range.

So far I added a 9 gram hosel weight to my 3-iron and a 2 gram hosel weight to my 4-iron and they matched up almost perfectly. I’ve got 4-clubs waiting for the epoxy to cure right now, and I’ll do the last 4 clubs tomorrow.

3JACK

46

Richie
Can you walk me through using that formula?

47

Macs,

Your problem is that you cannot use the mass of the grip and shaft together in the calculation.
The way you did it would only be valid if all the mass of the grip was evenly distributed along the length of the shaft.

So, the formula quoted above ignores the grip.

You should use MOI = (length of club in cm)(length of club in cm)(head weight in kg + trimmed shaft weight in kg/3)

If you have no measurement of the trimmed shaft weight (I believe that your 125 grams is for an untrimmed shaft),
then use 125 grams * trimmed length / untrimmed length
i.e. just take the fraction of the shaft weight that you used to build the club.

If you wanted to try to account for the grip, you could add to the above formula the following
MOI of grip = (length of grip in cm)*(length of grip in cm)^(weight of grip/3)

But, I think this is a rough estimate of the grip contribution to MOI because it assumes that, like the shaft, the weight of the grip is very evenly distributed along its length. You know that is not true. Most of the weight of a grip is concentrated near the cap. And this is why, in fact, we can almost neglect the grip. Or, another way to think about it, all the grips add the same amount to the MOI, so just match the clubs without grips and they will remain matched after putting on the grips.

Make sense?

48

Photonn
i somehow missed reading your post above. I get it now. The MOI now comes to 2727 (9 iron head weight is 295) and swing wieght is D9.

Richie
If you have any un-epoxied components, can you please just post the numbers so we can see how does the formula stands against the machine.

My real question is also that I got a set of Cleveland CG Tour irons with Rifle 6.0 shaft and a set of MP 68 with KBS X shafts on boxing Day (OK that is Canadian) for a ridiculously low price. The CG Tours in particular are just a beautiful blade set. But both of these are about 30 gram lighter than the Mac VIPs. I have the option to return them and am still not sure that adding 30 gram in hosel weight is such a good idea.
Cleveland%20CG%20Tour%20-%20Tour%20Quality%20Irons.jpg

49

Your number of 2727 now sounds much more like it. My MOI has me at 2725. The epoxy and ferrule probably adds about 5-10 points when assembled.

You can add lead tape instead. You can put the lead tape on the back of the clubhead or wrap it around the hosel.

3JACK

50

Here are the specs achieved on the VIPS
MacGregor VIPs.JPG

51

Macs, I wouldn’t add 30g to the tip. Maybe 10g on your 3 iron stepping it up by 1g each club as the clubs get heavier. Too much weight in the tips can cause the clubface to turn over, bit like Lags analogy of the figure skater spinning faster when the arms are pulled in to the centre.

Am I reading right that the weight of the grip is not a factor?? Its common to have standard grips at 46g or 56g (70g even). 10g really doesn’t make any difference.??

52

I don’t think it is any coincidence that some of the finest strikers played very heavy gear. This concept is TOTALLY lost in today’s club designs. Everything is geared toward speed and not force… at a huge sacrifice for accuracy control both in distance control and left to right.

Hogan used very heavy heads from the best of my knowledge. Snead was said to have used a driver that weighed 16 ounces at one time. Knudson also used heavy gear as confirmed to me by John Henrick who knew him well and competed against him for years. I have personally held Moe’s clubs and at the time they felt silly heavy to me.

Are we seeing the likes of these kind of strikers again? I suggest not. Is it even possible to do this with light gear? I suggest not. Because the game used to be about accuracy being #1. It still is on most golf courses, certainly the good ones.

Again it should be noted that in setting up your gear, there is a difference between swinging and hitting. The stuff 3 Jack is talking about here is VERY critical for swingers. Not as much for hitters.

When you passively release the clubhead into impact with dead hands, all this stuff becomes so critical. Spining the shafts, and weighting balancing the heads and so on. Very critical.

If you are hitting… not so much. If you are firmly holding shaft flex through active releasing, you simply need a stiff shaft, and substantial weight in the head to pin the mass against the resisting shaft. You take that feel and then go play golf with it.

You can hand me any club and I will be able to hit the ball straight within two or three swings max. Once I feel the point of maximum force for that club in relation to how I swing, I’m good to go. In other words, how much shaft flex can I hold for the rotational speed I generate. By far the most critical element is the lie angle, then followed by the mass of the head, then the stiffness of the shaft in that order.

When I was swinging… there were clubs I simply could not hit. I would try hitting a friends clubs on the range and often hit the ball sideways.

One of the things I have been wanting to do is get a proper Hickory Set, and play with them. I would guess I could play quite well with them right out of the gate for the reasons described.

But of course it doesn’t hurt to have a set finely tuned and balanced, but the real improvement is always going to come from better swing technique first.

53

MOI.png

Simples.

54

not one mention of lie angle… or accuracy

55

opencls2.gif

56

Even a lefty driver…

I’ve seen it… :sunglasses:

57

Grip does make a difference. Part of what you need to find is the balance point. That changes when the grip is put on.

I have some Iomic grips that I use. I wanted to intall one on my driver. The driver had a 53 gram grip. My Iomic had a 51 gram grip. The MOI was off by about 15-20 points when I switched the grips.

Same with when I put one on my hybrid. The hybrid had a 48 gram grip. So when I put the 51 gram Iomic on, the MOI raised by about 20 points.

As far as the hitter vs. swinger stuff, I think MOI matching certainly applies and applies in an important way. Perhaps with ABS hitting, you have a more consistent amount of force you apply to the club. But, if that doesn’t match the MOI (in this case, the amount of force required to swing the club), now you have to guess more if your clubs are well off.

I will say this, it’s spooky to measure the clubs and see what clubs are well off. Those clubs are almost always the worst clubs a golfer hits in the bag. I’ve seen this with my own personal experience with 3 different sets and then with a couple of other people I’ve done this with.

3JACK

58

That graphic is amazing NRG.

Sam Snead said he won a bet one time playing with a tree branch he whittled into a club. I wish he could be here to tell us how he whittled all the critical factors into his throwback club. I’d pay hard money if I could see him play a match against today’s best players if they had to use the same whittled “equipment”, especially if they had to whittle their own clubs. What’s the point? Just the fun and chuckles. I believe Sam had the feel to do exactly what he claimed, whether or not his story is true. I happen to believe him; genius is as genius does; perfect or flawed, everything is an instrument to be played in a higher realm and right now if you’ve got the real stuff like he did. His virtuosity would seamlessly capitalize on the virtues of either wood, steel, or a combination, and minimize the handicaps of the materials, as true artists do. Imagine yourself whttling a selected branch that tells you, even while the twigs and leaves are with it in the tree, that it can hit your golf ball the way you want and you know you can apply your pocket knife to shape it to work with your feel to beat the stuffing out of eager suckers.

All that could be mistaken as a slam on the genuine effort good folks are putting into this interesting and informative MOI topic. Instead, it is only a small tribute to the clever folks who preceded both us and today’s amazing technical tools.

Thanks.

59

I just look at the MOI Machine like I do a swingweight scale, except this MOI Machine has a laser and digital readout. There are swingweight scales that are electronic as well.

While I think it’s a high tech, but it’s more of a different philosophy towards the heft of a golf club.

I know Lag has utilized progressive swingweights with his clubs, making the longer irons a little lighter than the short irons. I think it was because of what his feel was telling him. The MOI matching (and how the swingweight progresses) more or less backs up what Lag was feeling. I noticed the same thing as well as I could hit longer irons better with progressive swingweights. I also noticed that I could have the swingweight match in a set of irons and for whatever reason, hit a couple of irons noticeably worst than the rest of the set and hit one of the irons better than the rest of the set.

I just stopped believing it was in my head and started to believe that there had to be something to the club. MOI fitting and matching gave me the answers.

The one thing I noticed is that my 7-iron is now a D-6 swingweight, which would be considered very heavy. And I’m not participating in ABS. I think this shows that more golfers need a heavier club than they are using and would like to figure out why the old players who used heavier clubs, but swingweight matched them, still hit the irons better. And I generate 0-2 mph more clubhead speed than the PGA Tour average with my irons. I hit my 7-iron (36* loft) 170-175 yards and my 9-iron (44* loft) about 150 yards according to Trackman. And I’m using steel KBS shafts. So I’m not sacrificing power with my irons by having ‘heavy’ swingweight to them.

3JACK

60

I think its a really interesting idea for fine tuning a set, so long as it is not done without consideration of deadweight and club length first. I wasn’t joking when I said I would be building a set to those specs. I have some already that are a prog SW but would like to try some with a slightly lighter dead weight in the long irons than Lags specs.