Swing Weight Scales

[zeke66]

My local shop which is kind of the Mecca for Southern California golf stuff measures clubs to 2-3 sw points higher than the local true spec store. Any idea why? Meaning the same club will be D5 at the golf shop but D3 at True Spec. Noticed this on 2 clubs. 

[P.E.]

That is strange.

 

Have you watched while they measure the swing weights?

 

[zeke66]

Ha yeah I’ve done it myself even. 

[Nessism]

Pretty common really.  I think Golf Mechanix sells a calibration standard.

[LCP]

My local club champion has a sticker on theirs +1 SW, so they know theirs is off by that much.

[HiTrajLoSpin]

There are 500 inch-gm between A0-B0, B0-C0, C0-D0, etc. , so that corresponds to 50 inch-gm between A0-A1, B0-B1, C0-C1, etc.

 

Therefore, an error of 2 SW points (e.g., D2 vs D0) is equal to 100 inch-gm. D0 is equal to 6050 inch-gm,

so an error of 100 inch-gm corresponds to an error of 100/6050 = 0.0165 or 1.65% .

 

Is that too much? Seems somewhat high, considering that an error of 1 lb. out of 150-250 lbs (0.66% - 0.40%) on your household scale is probably expected.

Edited January 18, 2021 by HiTrajLoSpin

[5baytjd]

If you have an accurate scale (postage or kitchen) that measures in grams, you can check it yourself utilizing the on-line swing weight calculators. 

 

Weigh it, find the balance point, measure from there to the butt end of the club; and put those two values into the calculator.

[Howard_Jones]

58 minutes ago, 5baytjd said:

If you have an accurate scale (postage or kitchen) that measures in grams, you can check it yourself utilizing the on-line swing weight calculators. 

 

Weigh it, find the balance point, measure from there to the butt end of the club; and put those two values into the calculator.

THIS.....

Here is how too...

Take the club and let it rest on one finger so you can find the approximate BP
Now set a piece of painters tape around the shaft at that spot.

Now take a knife and place it in a vise, edge up. (dont have to be very sharp)
Move the club back and forward on the edge of the knife until you find the exact BP where the club can rest flat without your support. (1 mm matters, just run numbers plus minus 1 mm and see what happens)

When BP is found, PRESS the club down against the knife blade, so you get a measure mark in the painters tape, NOT the shaft (thats why we added the tape)

Now take a ruler and place it in against a wall as point zero, and set the clubs grip end against the same wall, and measure distance down to BP i millimeters (remember to take notes)
Put the club on a gram scale and take notes of its total wgt.

Now go to this webpage, and enter Total wgt and distance to BP and you get a return value.
The calk is 100% and just as good as you are able to measure BP, and it takes a fool to get a return thats not within 0.25 SWP of actual when you do it like i describe here, ive checked a endless numbers of times up against my Mitchell SW scale who is the Benchmark here

http://www.leaderboard.com/SWINGWT.HTM

[Nessism]

Calculating swingweight works perfectly, but realize that the accuracy of the value is only as good as your measurements.  To assure good accuracy you need a scale that's accurate to within 1 gram and you need to be able to measure balance point to within 1mm.  No easy feat.  

[HiTrajLoSpin]

2 hours ago, Nessism said:

Calculating swingweight works perfectly, but realize that the accuracy of the value is only as good as your measurements.  To assure good accuracy you need a scale that's accurate to within 1 gram and you need to be able to measure balance point to within 1mm.  No easy feat.  

 

When I first read your measurement tolerances (1 gm and 1 mm), my thought was "those are way too small". However, doing the calculation shows that the best absolute error that can be expected with such tolerances is about 0.5 SW points ... wow!

 

Propagation of error shows that when a result is the product of 2 quantities (i.e., distance x weight in this case), then the relative error in the result is the sum of the relative errors in the individual quantities. Let's assume that the club to be measured is a 5-iron, 38 inches long, weighing 400 grams, balance pt 29 inches, and SW D0.0 .

 

Using your above tolerances of 1 mm in length and 1 gm in weight gives:

 

relative error in length measurement = 1/(25.4 x 29) = 0.00136

relative error in weight measurement = 1/400 = 0.00250

relative error in SW (i.e., inch x gm) = 0.00136 + 0.00250 = 0.00386 or 0.386%

 

D0 = 6050 inch-gm, so the absolute error in the overall SW measurement is 0.00386 x 6050 = 23.3 inch-gm

 

1 SW point (e.g., D1 - D0) = 50 inch-gm , so the absolute error using your above tolerances = 23.3/50 = 0.467 SW points

 

No wonder SW scales can easily give results that are off by 0.5 SW points or more!

Edited January 18, 2021 by HiTrajLoSpin

[pt73]

18 hours ago, Howard_Jones said:

THIS.....

Here is how too...

Take the club and let it rest on one finger so you can find the approximate BP
Now set a piece of painters tape around the shaft at that spot.

Now take a knife and place it in a vise, edge up. (dont have to be very sharp)
Move the club back and forward on the edge of the knife until you find the exact BP where the club can rest flat without your support. (1 mm matters, just run numbers plus minus 1 mm and see what happens)

When BP is found, PRESS the club down against the knife blade, so you get a measure mark in the painters tape, NOT the shaft (thats why we added the tape)

Now take a ruler and place it in against a wall as point zero, and set the clubs grip end against the same wall, and measure distance down to BP i millimeters (remember to take notes)
Put the club on a gram scale and take notes of its total wgt.

Now go to this webpage, and enter Total wgt and distance to BP and you get a return value.
The calk is 100% and just as good as you are able to measure BP, and it takes a fool to get a return thats not within 0.25 SWP of actual when you do it like i describe here, ive checked a endless numbers of times up against my Mitchell SW scale who is the Benchmark here

http://www.leaderboard.com/SWINGWT.HTM

Many thanks for this Howard.

 

Absolutely brilliant, checked my 25+ year old Golfsmith and it's within 1/2 point of the calculation using grams and mm for accuracy.

[Curious]

On 1/17/2021 at 8:13 PM, Nessism said:

Pretty common really.  I think Golf Mechanix sells a calibration standard.

They do. But when you buy a digital model the machine comes with a calibration weight(500 G)

Golfmechanix

Edited January 19, 2021 by Curious

[geochitown]

I purchased the calibration standard (swingweight, static weight, frequency and some other paramets) from Golfmechanix.

I've seen the same variation to other people's scales (off by up to 2.0 points).

 

 

[Curious]

First thing would to be check if the machine is leveled.

https://www.golfworks.com/images/art/GM1008.pdf

 

Please note: The weighing tray should hang freely so it can swivel unrestricted. Reading the Bubble for precision 0 +/-0 Grams level -3 Grams Back tilt +3 Grams Forward tilt.

 

SETTING UP IMPORTANT NOTE: Placing the base on a level surface is required. For each 1/8" that the scale is off level, the accuracy of the scale is changed by one (1) swingweight point. Surface should be checked with a level or bubble level.

 

 

[geochitown]

11 minutes ago, Curious said:

First thing would to be check if the machine is leveled.

https://www.golfworks.com/images/art/GM1008.pdf

 

Please note: The weighing tray should hang freely so it can swivel unrestricted. Reading the Bubble for precision 0 +/-0 Grams level -3 Grams Back tilt +3 Grams Forward tilt.

 

SETTING UP IMPORTANT NOTE: Placing the base on a level surface is required. For each 1/8" that the scale is off level, the accuracy of the scale is changed by one (1) swingweight point. Surface should be checked with a level or bubble level.

 

 

 

important check, not hard to maintain the bubble in the center of the levelness indication

[joostin]

I tote this swingweight spreadsheet calculator around.  Just sharing if you like to record multiple clubs in Excel format like me.  See the first tab:

 

Swingweight_Torque_Calculator_20201223 (1).xlsx

 

Baseline D0 = 213.5 oz-in (6052.6 g-in) per a few references including Tutelman.  I use Howard's method on knife edge meticulously balancing and measuring.  I used to use http://www.leaderboard.com/SWINGWEIGHT but didn't like how it would sway readings like a physical scale.  That site comes out about 1/2 a SW lower than my spreadsheet, but you can use the data however you like (like round to nearest whole number).  Someone made a nice spreadsheet that I based this on, but I just wanted to make my own version that I can keep improving and experiment with.  Slower than a scale, but useful recording method and never needs calibration!

[Howard_Jones]

On 1/18/2021 at 8:53 PM, HiTrajLoSpin said:

 

When I first read your measurement tolerances (1 gm and 1 mm), my thought was "those are way too small". However, doing the calculation shows that the best absolute error that can be expected with such tolerances is about 0.5 SW points ... wow!

 

Propagation of error shows that when a result is the product of 2 quantities (i.e., distance x weight in this case), then the relative error in the result is the sum of the relative errors in the individual quantities. Let's assume that the club to be measured is a 5-iron, 38 inches long, weighing 400 grams, balance pt 29 inches, and SW D0.0 .

 

Using your above tolerances of 1 mm in length and 1 gm in weight gives:

 

relative error in length measurement = 1/(25.4 x 29) = 0.00136

relative error in weight measurement = 1/400 = 0.00250

relative error in SW (i.e., inch x gm) = 0.00136 + 0.00250 = 0.00386 or 0.386%

 

D0 = 6050 inch-gm, so the absolute error in the overall SW measurement is 0.00386 x 6050 = 23.3 inch-gm

 

1 SW point (e.g., D1 - D0) = 50 inch-gm , so the absolute error using your above tolerances = 23.3/50 = 0.467 SW points

 

No wonder SW scales can easily give results that are off by 0.5 SW points or more!

You got it right, now imagine what happens when someone forgets to check LIE angles before dryfit, and later find a few heads that needs a adjustment of 2* maybe more?...or if you dont get the split grip fully seated before you put the club on the SW scale during dryfit? or that a "jig" was used to cut all shafts to the same exact slope of 0.5" and hosel specs was plus minus 1 mm for insert and BBGM?...or grip weight tolerances of plus minus 3.5 grams? and how often have you seen a set where the total wgt slope was good?

its quite a job to build a set to tight tolerances for all specs when we dive into the details like this, but if you want to make it as good as possible, here is my tips to how too...just follow the link.
 

 

[Nessism]

10 hours ago, joostin said:

I tote this swingweight spreadsheet calculator around.  Just sharing if you like to record multiple clubs in Excel format like me.  See the first tab:

 

Swingweight_Torque_Calculator_20201223 (1).xlsx 221.96 kB · 5 downloads

 

Baseline D0 = 213.5 oz-in (6052.6 g-in) per a few references including Tutelman.  I use Howard's method on knife edge meticulously balancing and measuring.  I used to use http://www.leaderboard.com/SWINGWEIGHT but didn't like how it would sway readings like a physical scale.  That site comes out about 1/2 a SW lower than my spreadsheet, but you can use the data however you like (like round to nearest whole number).  Someone made a nice spreadsheet that I based this on, but I just wanted to make my own version that I can keep improving and experiment with.  Slower than a scale, but useful recording method and never needs calibration!

 

Nice!  I also noticed inaccuracy in the Leaderboard calculator after doing a deep dive creating a "calibration club" (for swingweight, loft, and lie.)  There is a similar spreadsheet posted in the archives which I used instead.  

 

When measuring balance point I put a horizontal line against the wall near my balance point determination spot which was used to make sure the shaft was balancing perfectly level.  Little details matter if you want the most accurate measurement.  

[HiTrajLoSpin]

After reading David Tutelman's instructions for building a DIY SW scale, and then doing some thinking about his calibration procedure, I think that I've come up with a DIY method for accurately calibrating a Mitchell TourGauge SW scale (which I just purchased).

 

Now, like me, your first thought is probably that Mitchell already has a procedure for SW calibration: position the sliding Balance Weight at 0 on the Balance Beam Scale, and then adjust the rotating Zero Balance Beam Weight until the Balance Beam is level. However, that procedure only ensures that its SW measurements are reproducible and accurate relative to whatever SW calibration that the TourGauge was delivered to you. And after reading the discussion in this thread, it should be obvious that despite the precision CNC manufacturing of the TourGauge scale, the calibration of your delivered instrument probably is not absolutely accurate due to non-zero manufacturing/assembly tolerances.

 

So, if you would like to ensure a TourGauge calibration that can give reproducible SW measurements having a known accuracy, I think that the procedure below should provide that. The procedure requires:

 

     A weighing scale (preferably digital) having a capacity of at least 500 gm and accuracy of 0.1 gm or better

 

     A wood screw (or similar pointed object) whose length is determined by the distance between top of the weighing scale platform and the bottom of the Mitchell Balance Beam

 

     A small indentation (of the type that would be made by a center punch) on the bottom of the Balance Beam, located a known, exact distance from the fulcrum.

 

     In the example pics below, I haven't actually made an indentation (yet). Instead, I've simulated the method by placing the screw just below G0.0 on the Balance Beam, which is ~10.25 inches from the fulcrum. 

 

-------------------------------------------------------

Below are the steps in the DIY calibration procedure:

 

     1. Use the standard Mitchell procedure to level the Balance Beam using the rotating Zero Balance Beam Weight

 

     2. Turn on the weighing scale, place the wood screw (head down) on the approximate center of the platform, and then Tare (zero) the weighting scale

 

     3. Position the weighing scale and screw, so that the tip of the screw rests in the 10.250-inch indentation on the bottom of the Balance Beam, and so that the Balance Beam moves freely near the middle of its vertical motion on the balance indicator

 

     4. Move the sliding Balance Weight of the Mitchell scale to a SW reading of B0.0 (5050 inch-gm)

 

     5. Adjust the rotating Zero Balance Beam Weight until the weighing scale reads 492.7 gm (i.e., 5050 inch-gm/10.25 inch)

 

     6. Repeat the entire procedure a few times until consistent results are obtained

 

---------------------------------------------------------

After the DIY calibration, the absolute accuracy of the TourGauge is determined by:

 

     A. The accuracy of the weighing scale (assume 0.1 gm)

 

     B. The accuracy of the location for the indentation (assume 0.2 mm)

 

     C. The accuracy of locating the sliding Balance Weight on B0.0 (assume 0.2 mm)

 

From the discussion above in this thread, it's possible to make an estimate for typical absolute calibration accuracy

 

     relative error in weighing scale measurement = 0.1/492.7 = 0.000203

     relative error in indentation location = 0.2/(25.4 x 10.250) = 0.000768

     relative error in Balance Weight location = 0.2/(25.4 x 4) = 0.00197  (the B0.0 indicator mark is ~ 4 inches from the fulcrum)

     relative error in SW = 0.000203 + 0.000768 + 0.00197 = 0.00294 or 0.294%

 

For a typical club having a SW = D0.0 = 6050 inch-gm, the absolute error in the overall SW measurement is then 0.00294 x 6050 = 17.8 inch-gm

 

1 SW point (e.g., D1 - D0) = 50 inch-gm , so the absolute error using your above tolerances = 17.8/50 = 0.36 SW points

 

-----------------------------------------

Finally, it would be nice if Mitchell would modify the TourGauge by adding a tapped hole on the underside of the Balance Beam, located an exact, known distance from the fulcrum, so that a user could insert a threaded object of some sort for easy DIY calibration of this type.

Edited January 20, 2021 by HiTrajLoSpin

[Pepperturbo]

Different scales and maybe formulas = different data, then add man's involvement.  Nothing is a sure thing then. lol 

 

SW is like loft and lie measuring.  In theory all measuring equipment should come up with the same readings.  However, because "man" is involved, equipment varies, and conditions of equipment varies, and their installation varies, especially so from what is used by OEM.  Even the same pieces of equipment at different locations can read differently.  Pick one to rely on and go there regularly.

Edited January 20, 2021 by Pepperturbo

[JCAG]

The old Professional Clubmakers Society had both a swingweight and a frequency calibrated device (club) so PCSers could adjust/calibrate their swingwieght and frequency machines (via a software spread sheet) so all PCSers were operating off the same standard.

 

Frequency machines varied quite a bit and there were different clamp sizes. 

Edited January 20, 2021 by JCAG

[joostin]

9 hours ago, Nessism said:

 

Nice!  I also noticed inaccuracy in the Leaderboard calculator after doing a deep dive creating a "calibration club" (for swingweight, loft, and lie.)  There is a similar spreadsheet posted in the archives which I used instead.  

 

When measuring balance point I put a horizontal line against the wall near my balance point determination spot which was used to make sure the shaft was balancing perfectly level.  Little details matter if you want the most accurate measurement.  

I'll try that line on the wall.  I just eyeball againt the bottom edge of a mirror on the wall but could be crooked.  On the gram scale I always weigh 2-3 times, then try to split hairs on the mm side of the ruler.  May be a little OCD!  IMO the Leaderboard calc just needs to calculate one number, so I don't think they needed to bother teeter totter and could've shown 1/2 swingweight increments... hence the Excel calc.

[JCAG]

https://www.ebay.com/itm/Golfsmith-Swing-Weight-Scale/303852845825?hash=item46bf0a7b01:g:URoAAOSwcipgBe9p