The drop-weight principle is likely (exact data probably doesn’t exist…) the most widely used tensioning principle in stringing machines. It requires few mechanical parts, no recalibration, and, unlike crank-based systems, for example, it’s a so-called constant pull principle. This means the string is continuously held under tension, which compensates for initial string stretching and thus yields very consistent and precise results in the final strung stiffness of the racket.
First, it’s worth taking a brief look at the theory behind the entire drop-weight principle. And for those with a fondness for mathematics and physics, I recommend reading the following page at this point:
https://tt.tennis-warehouse.com/index.php…
In Brief:
The system is so precise and consistent because the only variable is actually the weight’s position on the arm. In contrast, the geometry of the tensioning mechanism and gravity remain constant. This means that once a drop-weight machine is correctly calibrated, nothing about it changes afterward.
For the set tension to be accurately pulled, the drop-weight arm must balance itself horizontally. Deviations up or down will result in a reduction of tension, though this is less dramatic than one might assume.
An Example:
Set Tension: 10 kg
Deviation of the Drop-Weight Arm from Horizontal: 10°
Resulting Effective Tension: 10 kg x cos(10) = 9.85 kg
This means you still achieve very accurate readings, even if the drop-weight arm balances a few degrees above or below its ideal position.
However, the system isn’t entirely straightforward to operate and offers numerous opportunities for user errors that can have serious consequences for the stringing result, and even risk damaging the racket.
Given recent events, I’d like to point out a seemingly not-so-rare, but quite catastrophic mistake in the use of drop-weight machines: The drop-weight arm is manually pushed down when it stops above the desired horizontal position.
Many will groan now and say, “Well, it’s totally obvious that’s not right!”, but reality shows that this is done now and then, and the “perpetrators” are completely unaware of the consequences of this supposedly minor manual “assistance.” To clarify, a short video (thanks to user “EndFX” from BadmintonCentral!) now follows, which demonstrates, with the help of a digital scale, how much additional weight is applied to the string, and thus the racket, with just slight manual “assistance”:
https://www.facebook.com/Saitenkiller/videos/2217638331605780/
Since the numbers aren’t optimally visible, here they are in writing:
- Measured tension when balanced: ~9.8 kg
- With “manual assistance”: ~13.5 kg
Now, imagine this with a set tension of 12 kg or more. You could easily reach values of 16 kg or more. And then it’s hardly surprising if the string, or even worse, the racket doesn’t survive. And incidentally, every string job becomes a pure lottery when it comes to the resulting hardness.
Therefore, a final emphatic warning to all drop-weight users:
Never, but truly N E V E R, push the drop-weight arm down manually. You seriously risk breaking the racket or the string and completely negate any consistency in your string jobs from the outset!
And finally, a small YouTube find that also clearly shows how not to do it. As described, it’s not too dramatic if the drop-weight arm doesn’t end perfectly horizontal – but it certainly shouldn’t rest on the table. Amusingly, the video comes from the Badminton World Federation’s channel – and rumor has it that the “perpetrator” is a very experienced stringer who otherwise has no contact with drop-weight machines anymore. So, the principle – as simple as it may seem – clearly has its pitfalls that you need to be aware of.