Easy, cheap, and accurate racket matching

Discussion in 'Strings' started by Irvin, Apr 28, 2010.

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What do you think of this?

  1. Love it

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  2. Leave it

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  1. Irvin

    Irvin G.O.A.T.

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    Ever want to match your own rackets but don't have $1,500 to $5,000 to shell out for the equipment? Those machines measure the balance point relative to the head of the racket and a point 10 cm from the butt cap. Why 10 cm? Because that is the average point where the racket pivots in your hand. That is the point where center of the average player's index finger knuckle hits the racket. Well I am not average and I bet you aren't either.

    Long story short here is the device or cradle made with two home depot angle brackets and a scrap piece of wood. I placed the brackets so one is higher than the other and the left one is 10 cm from the inside of the right one.

    [​IMG]

    I have a postal scale and first I get the overall weight of the racket - 343 grams (12.1 ounces.) I used grams because I think the scale is more accurate that way.

    Now I put the cradle I made on the scale and zero the scale. Then I put a spacer under the head of the racket to hold the racket level and put the racket in the cradle to measure the weight - 215 grams. See that small line to the right of the balance point on the angle bracket? That is where my first knuckle hits. I could move the balance point to there to match the racket to me.

    [​IMG]

    Then I take the cradle off the scale and zero the scale again. Place the cradle out in front of the scale and place the butt of the racket in the cradle and the tip on the scale to measure the head weight - 128 grams.

    [​IMG]

    So my racket is 343-215-128 grams (total weight - grip weight - head weight) in these three measurements. Get all three points to match up in your rackets and they will be matched. Space the angle brackets so they match up with the distance of the center of your index finger knuckle to you and your rackets will be matched to you. Modify the cradle so you can change the distance of the angle brackets and you can use this one device to match rackets for anyone.

    Just for the fun of it I used some calculation to try to figure out the distance from the cradle balance point to the Center of the racket balance point in the cradle and measured that distance in cm, squared the distance and multiplied that by the kg (0.343 kg.) I forgot exactly what the result was but I took the racket to PGA superstore and measured the RDC on their Babolat machine. I was 4 off - darn it. But I don't think you need all that.

    What do you guys think Love it or leave it? Come on guys over 100 lookers and only three voters don't forget to vote up top I would really like to know what you think.

    Irvin
     
    Last edited: Apr 28, 2010
    #1
  2. Lambsscroll

    Lambsscroll Professional

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    Nice post. I never thought of breaking down the racket like that and measuring the weight.
     
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  3. Irvin

    Irvin G.O.A.T.

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    By the way I will make you one of these for $5. Shipping and handling will be $10,000 and no local pickup is allowed. In short don't even ask. LOL

    Irvin
     
    #3
  4. Irvin

    Irvin G.O.A.T.

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    That is all they do when they measure with an RDC.

    Irvin
     
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  5. Lambsscroll

    Lambsscroll Professional

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    So I could pencil 10 cm on the handle and maybe use the pencil as the cradle. Then zero out the scale. Then weigh the handle. Would that work?
     
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  6. Irvin

    Irvin G.O.A.T.

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    Absolutely you do not need the cradle. You could use anything. BUT I feel it would be more accurate if you balance the grip on something thin like this bracket. I used two brackets so I could slide the butt of the racket or rackets right up to the higher one and keep the distance from the butt to the balance point exactly the same every time. When you start varying the distance you vary your accuracy.

    Irvin
     
    #6
  7. Irvin

    Irvin G.O.A.T.

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    You could also measure where the center of your first knuckle hits the rackets and use that as your balance point. That way your matched rackets are also matched to you. The picture below shows how I measured my distance. I gripped the racket a few times and took the average location.

    [​IMG]

    Irvin
     
    Last edited: Apr 28, 2010
    #7
  8. YULitle

    YULitle Hall of Fame

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    I've always been told, and this applies to most things, that of easy, cheap and accurate, you can only ever achieve two at once.

    i.e. road bicycles are only two of these three at one time: cheap, light and durable
     
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  9. Irvin

    Irvin G.O.A.T.

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    LOL You are probably right about that. When you figure in the price of the scale I guess cheap goes out the window. The more accurate you want this to be the higher the price of the scale. Sort of like use the bathroom scales you have and you have cheap and easy.

    Irvin
     
    Last edited: Apr 28, 2010
    #9
  10. MuscleWeave

    MuscleWeave Semi-Pro

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    Your cradle is very nice, but won't just a T-bracket at that point suffice? And the 10 cm point is really immaterial and distracting, unless you're balancing racquets for unknown players.

    I would be interested in a more detailed explanation of your measurement of RDC. I see mass and distance, but I didn't see any time measurement for your formula, and you arbitrarily squared the distance to the racquet balance point. Please explain. Maybe the 4 pt. RDC difference could be seen if you take the measurements at the 4" and 20" points.
     
    #10
  11. David123

    David123 Hall of Fame

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    haha nice find. I liek it.
     
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  12. Irvin

    Irvin G.O.A.T.

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    The Babolat RDC measurement is cm*cm*kg or cm2kg. cm is the distance from the 10 cm point to the balance point (or center of mass) out on the racket. All that is an assumtion on my part and you know what happens when you ass-u-me. LOL That center of mass is determined by how fast the racket rotates back and forth. I am not really trying to measure than balance point or center of mass. I did some ruff calculations but after talking to a physics PHD my theory was flawed. If the rackets are matched thought the weight at all three points will be the same. So I am not trying to come up with the RDC measurement because I don't know how to do that to tell you the the simple truth.

    Let me say that the balance point I am talking about is not the normal balance point of the racket but the center of mass relative to the 10 cm point and the head of the racket. That is hard to determine until you use some pendulum calculations. When you start doing that your accuracy is going to go south unless you have something that can accurately measure the rate of swing.

    And yes anything you balance the racket on will work fine. I wanted something thin and something I could repeat over and over that would guarentee me the same distance from the butt of the racket. Consistancy is key here for multiple rackets. Like the 'Lambsscroll' said you could use a pencil if you wanted.

    I made this last year and it has been sitting on a shelf for a while. I will have to see what it was I did to come up with the RDC measurement and try to get back with you but it will be next week. I am out of town for the rest of the week with no PC access. I used the weights ratios to come up with a distance to the center of mass I can tell you that much. Squared the distance and multiplied that times the mass.

    Irvin
     
    Last edited: Apr 28, 2010
    #12
  13. Octavianus

    Octavianus Rookie

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    Irvin, this is brilliant.
     
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  14. MuscleWeave

    MuscleWeave Semi-Pro

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    Now I'm gonna have to find a Physics textbook to review how moment of inertia formulas work. I love this stuff! Come to think of it, wouldn't the moment arm extend from the 10 cm point to the middle of the sweet spot? Or no, that's the point of impact. The inertia of the racquet (swingweight) would be measured at the balance point. It has nothing to do with the ball. I used to derive my own formulas from the units of the answer, like you did, when I was in college.
     
    Last edited: Apr 28, 2010
    #14
  15. bsandy

    bsandy Hall of Fame

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    That's assuming your fulcrum is at your knuckle.

    This is cool idea!! Since tennis is played in the six inches beween your ears, I'm sure it works just fine, if you believe it does.

    I think that's the definition of Voodoo.

    Personally, if static weight and balance are the same, my head says the swing weight is the same.

    . . . Bud
     
    #15
  16. Irvin

    Irvin G.O.A.T.

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    This will get your started. http://www.myphysicslab.com/pendulum1.html

    Which knuckle? Remember some people have two handed backhands. LOL I agree with the 6" part completely.

    Irvin
     
    #16
  17. Sublime

    Sublime Semi-Pro

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    This technique will help match the balance point and weight (probably a little more closely). It won't, however, match the SW if that's what you're implying.
     
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  18. Irvin

    Irvin G.O.A.T.

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    When I get back in town nesxt week I will balance up my two rackets and see if the swingweights are the same on a Babolat RDC. I believe they will match up. I will let you know.

    Irvin
     
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  19. LPShanet

    LPShanet Banned

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    While it may work for your racquets (and some others), and the differences may be hard to measure, it won't be accurate for swingweight on all racquets. The problem with a weight/balance only system is that you can "trick" it with different distributions. The reason swingweight is important is that you can have infinite different racquets with the same static weight and multiple balance points, but still have distribution be different. Still, if you don't want to drop a ridiculous wad of cash, your device could be a great tool for private/home stringers who want to add at least some level of matching.
     
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  20. MuscleWeave

    MuscleWeave Semi-Pro

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    The swingweight of a racquet has nothing to do with pendulums and motion. It's a statics problem. With all due respect, please stop posing.
     
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  21. Irvin

    Irvin G.O.A.T.

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    Swingweight works on a pendulum theory. According to what I have seen weight make no different it is only the distribution of weight that matters. So if I hung a 1 pound ball on a two foot string and would swing at the same rate as a steel bar that had the center of mass two foot down. Like I said when I get back I will do some more testing but thank you for your thoughts.

    The RDC units measure the weight distribution by swinging the racket and measuring the center of mass. I am trying to do that backwards. By measuring the center of mass and matching it in two or more rackets I think the swing weight will be the same.

    Irvin
     
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  22. Sublime

    Sublime Semi-Pro

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    Irvin,

    The problem is, you are not measuring weight distribution, just the center of mass and weight of the racket. Let's say you took two rods that were perfectly stiff, the same weight, and had identical balance points. One having 90% of its weight located within an inch of its balance point and the other one having close to an equal distribution of weight. Those two rods would measure identically on your apparatus, would have very different SWs.

    If you sawed those two rods in half, and measured the 4 pieces on your apparatus, you'd see different results for the pieces and definitely between the pieces of the two rods. The reason you'd see a difference is because the balance points of one half of the each of the original rods will be drastically different.

    Like LPShanet said, we're not saying the SW won't be close or even match with two rackets of the same model, matched with this system. However, it's certainly not a given. The results will be no closer than if you matched the racket's weight and balance point by any means, as long as that means was accurate.

    Now if you want to saw both rackets in half and match each half, the SW will be a little closer ;) (but still not a given that they'd be the same).
     
    Last edited: Apr 29, 2010
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  23. LPShanet

    LPShanet Banned

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    As Sublime points out, you're partly right and partly wrong. The simplified calculation made assumes even distribution, but the problem is that you can achieve the same effect by distributing the weight in chunks, parcels, etc., which will produce different swingweights. The system you've devised doesn't allow you to adjust for differences between the two.
     
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  24. Irvin

    Irvin G.O.A.T.

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    Well I took my rackets to have the swing weight checked this morning. One was 334 and the other 327. I brought them home the the one with the lighter weight weighed 2 grams less than the other. I added lead tape to the lighter racket and got the two rackets to weight the same for total weight, head weight, and fulcrum point weight. I took both rackets back to have the swing weight checked again. Both rackets are now 334.

    But I think I got lucky to get the same readings on both of the rackets. My scale measures in whole grams only so the weight measurements could be off by plus or minus 1/2 gram. I guess I could add small weights to the scale and see at what point the scale goes up a gram but I am not sure it is needed. This is close enough for me.

    Irvin
     
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  25. Irvin

    Irvin G.O.A.T.

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    Nothing could be further from the truth. The rod that had 90% of it weight at one point would weight much more when the weight the weight moves closer to the point being measured. Remember the majority of the weight will not be moved 10 cm towards one end and away from the other. This method is all about weight distribution.

    Irvin
     
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  26. Sublime

    Sublime Semi-Pro

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    Irvin, what I said is true and is basic physics. A rigid object will act as though all of it's mass is at it's center of mass, regardless of its distribution.

    Now, you start rotating that object with an angular velocity and the actual distribution of the weight becomes very relevant. But you can't measure one with only the other.
     
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  27. Irvin

    Irvin G.O.A.T.

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    This time I completely agree with you except for the part that what you said last time was correct. Let's assume that we have two rackets one weighs 12 ounces and the other weighs 9 ounces and both are 4 points head lights. If we add 3 ounces of lead tape (this is not 90% of the weight but only 15%) on the 9 ounce racket at the balance point both racket will weigh the same and both will have the same balance point. But will the swingweights be the same ABSOLUTELY NOT. The racket that originally weighed 12 ounces will have a higher swingweight.

    With my cradle when you weigh the 12 ounce racket on the butt end 10 cm from the butt cap the racket will weigh less so the center of mass will be farther away from the fulcrum point. When you weight the 9 ounce racket on the butt end will will weight more because 25% of the mass is now 10 cm closer to the butt cap end of the racket. If the butt handle end weighs more and the head weighs less the center of mass is closer to the fulcrum point. Swingweight is the distance between the fulcrum point to the center of mass squared time the total mass. If the distance is shorter the sweing weight will be less.

    In order to get these two rackets to have the same swing weight the 3 ounces of lead tape will have to be placed at a point where the fulcrum weight and the head weight will be exactly the same in both rackets. If the center of mass is the same in both rackets the weight at the fulcrum point and the head will be the same. If the center of mass (relative to the fulcrum point) and the mass are the same and the total weight is the same the swing weights are the same.

    Do not misunderstand me now I am not talking about balance points end to end of the racket. That is something completely different. I am talking about the first moment which is relative to a fulcrum point some distance up from the butt of the racket. It could be 10 cm which is the industry standard or it could be the axis point where the racket rotates when you swing the racket. I think that point is different than 10 cm. It could be different for your backhand and forehand especially if you have a two hand backhand.

    Irvin
     
    #27
  28. insiderman

    insiderman Rookie

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    'Tip-weight' has been used for many, many, many years - prior to electronic better diagnostic equipment - for taking 'static' measurements, it isn't 'bad', but it isn't as accurate as measuring actual MOI. Very few things are "invented" these days - more so just revised additions of old practices used long ago...
     
    #28
  29. Irvin

    Irvin G.O.A.T.

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    Never knew that 'insiderman' thanks for the information. I was just looking for a way to compute the MOI or center of mass relative to a fulcrum point where the racket is gripped and did not want to buy any expensive equipment.

    Irvin
     
    #29
  30. GPB

    GPB Professional

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    Is this method any better or worse than TW's pendulum method?

    I've got two rackets that I *think* are matched, and maybe that's the most important thing. If I mess with them and realize they're different, it'll mess with my mind!

    But anyways, I have two rackets that I've "matched" their static weights and balance points. Adding the tip-weight to my calculations can't hurt anything, can it?
     
    #30
  31. Irvin

    Irvin G.O.A.T.

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    I am not sure any method is better than another method. I did not like the TW method because it measures the center of mass relative to the head and not a fulcrum point where you grip the racket. Also the pendulum method may or may not be easy to time. So I opted to try to find the center of mass relative to the first knuckle where I specifically grip the racket.

    Irvin
     
    #31
  32. bsandy

    bsandy Hall of Fame

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    It's like voodoo. If you think it works, it works.
     
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  33. Bud

    Bud Bionic Poster

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    If you have two of the same racquet model... simply matching their weight and balance will give almost identical swingweights.
     
    #33
  34. GPB

    GPB Professional

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    I have to agree with you, based on my findings so far. My C10Pro racquets are "good enough" for me. But what about the Vantage that I'm trying to match them to? Next time I feel like messing with them, I think I'll use Irvin's idea here.
     
    #34
  35. Irvin

    Irvin G.O.A.T.

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    Bud and GPB, I don't doubt you are probably right. But matching the balance accurately is harder than it sounds. Let's say I had two rackets that were evenly balanced and both weighed 340 grams. If they were evenly balanced the head weight and butt weights would be 170 grams each. This is the weights measured from both ends and not with the fulcrum. But if ones head weight was 172 grams and the other was 168 grams I bet they would both look evenly balanced on a balance board. It is easier to see the difference measuring the weight.

    Irvin
     
    Last edited: Jun 6, 2010
    #35
  36. gflyer

    gflyer Professional

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    Irvin,
    I am not an expert but I do think that your idea is brilliant and could be very helpful for home users (like me).
    I am struggling trying to match my three frames using balance board and scale.
    I think your system could help me here. I will try in the weekend.
    I do have one rookie question.
    How do I proceed to match the racquets once I have the three numbers for each of them?
    I guess first I figure the heaviest and so I know the weight to add to the other one(s).
    But then how do I decide where to add the weight to match the other two numbers?
    Should the weight be split between head and butt or all in one location?
    Sorry if my question is silly but I am still trying to digest this.
    Thank you!
    Cheers,
    g
     
    #36
  37. GPB

    GPB Professional

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    Well I figure with Irvin's method you have three balancing points (head, fulcrum, and handle). If you take your racket and get a reading for each point, let's call that A, B, and C. Now, whatever weight you add will affect each reading differently. You could figure out a formula reflecting this (and I was going to try to when I hit the "reply" button) but I think for now I'll just leave it at the hit-or-miss method. Try something and see what happens to your scales, then add some more mass somewhere else and see what happens then. Maybe somebody with a little more time on their hands can chime in on this formula.

    I think you'll see that added weight will have a larger affect on the scale reading at a given point the closer the weight is to that point.
     
    #37
  38. gflyer

    gflyer Professional

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    Thank you.
    I am looking forward to try this method because with balance board and scale I am getting frustrated. :-(
     
    #38
  39. Irvin

    Irvin G.O.A.T.

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    Unless you are going to start taking some drastic steps you are going to have to match the two lower weight rackets to the heaviest one. If one racket weighs 3 grams less and another weighs 5 grams less you will have to add 3 and 5 grams to those racket to get the total weight to come out the same. Where you add the weight depends on what you are trying to accomplish. If you want to add stability to the racket you should add the weight at the widest part of the racket. But adding all your weight at 3 and 9 o'clock may not make the other two reading come out correctly. Move the weights up and down by placing them on the strings until the numbers match up for you. It is possible that you may have to add weight to all three rackets to balance them out. If you are looking for power add some weight at 12 o'clock to bring the head weight up to the correct amount and add weight at the fulcrum point to being the fulcrum weight up.

    Not quite it is total weight, head weight and fulcrum weight. Figuring out the weight of the handle would be difficult.

    The balance board is a little frustrating. You could have three rackets all 6 points head light but they could be 6.4, 6.0, and 5.6 points head light. An easier way to do that is to measure the head weight and but cap weight. Then add weight to the racket to get the total weight, butt cap weight, and head weight all the same.

    Irvin
     
    #39
  40. gflyer

    gflyer Professional

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    Irvin you are very helpful and exhaustive...as usual.
    Thank you very much.
    g
     
    #40
  41. Bigtime

    Bigtime Rookie

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    Very interesting thread. I love the econo homemade device. I will have to revisit this thread someday when I have time to fiddle with my frames.:)
     
    #41
  42. GPB

    GPB Professional

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    Oops, I'm so embarrassed. Yeah, those measurements!

    I'm finally getting around to fine-tuning my rackets. I'll start with my C10Pro's, and I expect them to be very similar. Once I get them to a happy number, I'll add my Vantage to the mix and see how things look. Hmm... do I REALLY want all three of my rackets out of commission at the same time?
     
    #42
  43. iowaviking11

    iowaviking11 Rookie

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    sorry to bring up an old thread irvin, but i have a question. when measuring the total weight-head weight- fulcrum/handle weight, is the difference between the two the balance point of your racquet? also if i get the same head weight and fulcrum weight for two racquets the balance points should be the same for both correct? Just starting to read up on customizing my sticks and just have a couple questions to get started! Thanks
     
    #43
  44. iowaviking11

    iowaviking11 Rookie

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    one more thing when i have to add x amount of grams to head how do i know where to add it? is it at the 10 cm mark and the other end where my ruler is? what if i want the lead at 12? thanks
     
    #44
  45. Mazilla2219

    Mazilla2219 Rookie

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    Sorry to revive an old thread. I know Irvin has posted an updated method of matching racquets but this method seems alot easier for my non-pro 3.5 tennis game. My question is relating to this step. Irvin or anyone else, what spacer do you use and doesn't the spacer effect the measured weight of the grip end of the racquet?

     
    #45
  46. struggle

    struggle Hall of Fame

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    i have a similar rig. Well, not exactly but it does the same thing.

    I try to weigh the ends of the racket with the racket being "level" or horizontal.
    I think the key here is to be consistent.

    My spacer acts to hold the racket roughly level.
     
    #46
  47. Mazilla2219

    Mazilla2219 Rookie

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    struggle, do you rest the stringbed or frame on the spacer? I am picturing some foam padding or something to hold it level but wouldn't that change the weight that is being registered on the other end?

    Additionally, the sum of the head weight + grip weight = total weight right? Thus, couldn't you just measure the head weight and subtract that from the total weight to get your head weight?
     
    #47
  48. struggle

    struggle Hall of Fame

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    play with it and you will see.
     
    #48
  49. Irvin

    Irvin G.O.A.T.

    Joined:
    Mar 15, 2007
    Messages:
    12,093
    Location:
    Marietta, Ga
    Struggle is correct the spacer is only used to make the racket level. But matching racket this way only matches the balance points of the racket and the weight. The moment of inertia may then be close - maybe. The newer method is better. If you have SwingTool and RacquetTune, you can use SwingTool to check the MOI and RacquetTune to identify how to modify the rackets as you want. Total time maybe 10 minutes max.

    I can make a short video if you want. Just let me know. I mean really short maybe a couple of minutes max showing all the steps.

    1 - Measure hang point
    2 - Measure weight
    3 - Measure balance
    4 - Measure SW or MOI
    5 - Calculate what weight is needed where to match rackets.

    If you don't have SwingTool and RacquetTune I would imagine a stop watch and the TW tools would be your next best alternative.
     
    Last edited: Oct 7, 2014
    #49
  50. Mazilla2219

    Mazilla2219 Rookie

    Joined:
    Oct 2, 2008
    Messages:
    284
    Irvin, I saw on the other thread that you've already made a template worksheet to record all the readings. Could you possibly send that to me at v.nguyen2219 @ gmail dot com?
     
    #50

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