Category Archives: Testing Devices
Well, in the simplest terms, failure tells us it is time to have the request strung! However, there may be subtleties in string failure that can help us in our quest for tennis racquet performance.
Is the failure shear related or tensile strength related? Was friction the major contributor to the failure? Where did the failure occur (on the racquet, not the court)? Was the failure during play or in the bag?
Shear-related failure is when the string breaks very near the racquet frame. This failure is called a mis-hit or shank! It is like cutting the string with a pair of scissors!
Friction failure is caused by just that, friction! Friction is caused by the string moving on each other. That rubbing creates friction and notches the string where it will fail.
If the racquet failed during play and it is not shear-related, the tensile strength of the string was exceeded. If a string has a tensile strength of 120 pounds and the tension is 60 pounds leaving 60 pounds to be used to hit the ball. Some big hitters can generate at least that much force on a solid forehand!
This graph shows the tensile strength of the string to be about 115 pounds. Given the movement of this string-on-string, the frictional notching can contribute to relatively early failure based on the hitters force.
This graph shows the tensile strength of the string to be about 155 pounds but it has to travel (stretches) further to reach that force.
So, you can see, with this information we can make better decisions when asked to suggest a string, or strings, for a client!
If you have been following Racquet Quest online and with the podcast, you know we are very fond of data! In keeping with that “fondness,” we have received our newest testing device, which I have named “Questron.”
During the last week, we have spent time getting Questron set up to do the kinds of testing we think is important for the tennis player, the racquet technician, and anyone else that cares about numbers!
It will be about another week before posting any data because we are “tweaking” some connection points, cycle settings, and refining the data’s graphing.
We have over 400 strings to test; however, we will eliminate many of those strings not relevant to today’s tennis player.
Even in the “testing” phase, we are discovering interesting facts about strings that will help us put together the best setup for you!
This is the “base” Questron. Future versions of this device will incorporate the “Power Potential,” “In-Plane Stiffness,” and “Dynamic Stiffness” testing that is currently done on other equipment.
The StringMeter is a device used to check the tension of an individual string. There are other versions of similar functionality, but this is what we use, and I will start with that.
Interestingly, this device traces its design to a tool that is used to check mainstay tension on a sailing vessel.
It is clear that our devices are well used, so they must be a “friend,” not a “foe”! And to that, I would say yes! The two (2) units shown here are “calibrated” units. One device is “free string,” and the other is “strung string.” These are different scales and very important for accurate information.
When we evaluate string or stringing machines, one of the most important values is the string tension with only the main strings installed. Using the “free string” scale, we check every main string and record the number.
Once the racquet is fully strung, we can check some center main strings and center cross strings with the “strung string” scale and see the variation. The difference between the two is the “natural ratio” of the racquet.
In addition to the stringing machine review use of the StringMeter, we also use it to calculate our “accuracy index.”
For this, we use the “strung string” scale and check each main string tension from left to right and every cross string tension from top to bottom and compare the actual numbers to the calculated numbers based on a non-distorted racquet. This spreadsheet shows how accurately the ball will come off of the racquet face.
The “efficiency index” tells us how much the racquet needs to change shape to reach that “index.”
These are all essential functions of the StringMeter and String Tension Tester from Gamma Sports.
But, what if the StringMeter or other device is used without knowing what it is telling the user?
This is the “foe” part!
This would be the case if a customer with such a device has a racquet strung at say a reference tension of 55 pounds. The customer then uses the method to check the tension and finds that it is not 55 pounds or even close! The customer is not going to be happy!
If the customer knows what to do, they can check the main string tension as soon as they can after stringing, then, later on, to see how much the string has stretched without regard to the reference tension.
It is what it is!
When the racquet is no longer performing it would tell the customer how much the tension can deteriorate before stringing is required.
So, these devices are very useful for individual string tension but no so much for “string bed stiffness,” which is the total string bed as a ball impacts it.
We will look at some of the “string bed stiffness” devices in a future post.
Management is not just for adults! Juniors that play tournaments need to have some management skills! During this coronavirus slow down it is a good time to learn some of these management skills.
We see many different management slip-ups such as no racquets for the tournament tomorrow! All racquets have broken string and are at the bottom of a bag nobody wants to stick their hand into!
Juniors Management Tip #1:
Every Monday takes every racquet out of the bag. If one or more are broken leave them out of the bag.
Juniors Management Tip #2
To get some idea of how much longer the string may last simply try to move the 5th or 6th cross string by pulling up toward the top of the racquet. If you can not pull the cross string up it is time for stringing. If you are able to pull a cross string up pay attention to the “snap” it makes as you push it back into location. A serious “snap” indicates a deep notch.
Monofilament strings typically fail by notching which makes it difficult to move the cross strings. If your string is a multi-filament and looks like the picture on the left it is time to string!
What if neither of these conditions exists?
Every racquet in your bag should have a tag indicating when the racquet was last strung and if it has been more than one month it is time to string, period!
Just for fun you can go to our SFC function and get a good ideas as to how many times per year yu need to have your racquet strung.