Hardness Table (topsheet/sponge)

I just sent about 20-25 cuttings to Jim T's friend. If Jim T's friend is the one that is doing all the testing then we have one person that should be testing in a consistent way instead of each manufacturer doing their own tests their own way.  That is the whole point of this database.

http://www.npl.co.uk/engineering-measurements/mass-force-pressure/hardness/rubber-hardness

If you want dynamic results then simply skip the hardness stuff and try to find the coefficient of restitution in the normal and tangential directions as a function of impact speed and perhaps angle.  The coefficient of restitution is a true indication of how a rubber plays.  

vvu.tee wrote: i would like to regress a dozen of posts: it is so much easier to rely on gut feeling than measurement and math. "gut feeling" is actually a method of sorting and analyzing data subconsciously perfected by evolution for far-far longer than the entire history of mathematics and science...

True - but in order to rely on gut feeling you need to actually buy and test the rubber. Knowing in advance which rubbers are more or less in the range you prefer, should help.

For instance, when i am looking for a rubber to possibly replace PME 47.5 I know that I want

a) inverted
b) non-tacky
c) 2.1-2.2 mm
d) fast yet spinny and controllable enough...
e) low sensitivity
f) hardness should be around 38-40 degs on DHS scale (non-tensor)

almost all of this can be ascertained from manufacturer's data and reviews (usually regardless of the level of reviewer), except for speed/control. Low sensitivity and speed however could be guessed from non-tackiness and sponge/topsheet hardness, especially if sponge belongs to a new generation of SGE sponges.

So it helps to narrow the choices... doesn't solve everything, of course... but should help.

The 554 is supposed to be SST.

How is it that Pryde 30 degrees is 40 degrees?

JimT wrote: Butterfly Tenergy 05 2.1 black                       28/22

does this mean the topsheet of tenergy is harder than the sponge? it certainly does not feel like that...

seguso wrote: JimT wrote: Butterfly Tenergy 05 2.1 black                       28/22 does this mean the topsheet of tenergy is harder than the sponge? it certainly does not feel like that...

What can I tell you... them's the numbers.

Remember that the measurement is done on a very (relatively) thin sheet of rubber/sponge. Naturally this means that hardness number of topsheet will surely be dependent on hardness of sponge - after all almost as soon as the durometer starts pushing into the topsheet the sponge will come into play.

So - once again - these numbers are not supposed to coincide with the "real" numbers from manufacturers, but they should useful for general comparison (between teh numbers in the same table - this one, that is).

slevin wrote: Rakza 7:     27 / 26 Rakza 7 soft:     27 / 25 Tenergy 05 FX:     26 / 21 Tenergy 05:     28 / 23 Vega Pro:     29 / 20 I may have found a BH rubber (R7S - didn't know that it isn't that soft at all) using this table, thanks! I also didn't know that XVP sponge is that soft. Also, could you if possible, please specify which Narucross GS version is tested here?

Unfortunately I cannot add these numbers to the table as the measurements were not done by the same durometer, using same technique.

Remember that the measurement is done on a very (relatively) thin sheet of rubber/sponge. Naturally this means that hardness number of topsheet will surely be dependent on hardness of sponge - after all almost as soon as the durometer starts pushing into the topsheet the sponge will come into play.

Edited by chopchopslam - 06/15/2012 at 12:01pm

chopchopslam wrote: Remember that the measurement is done on a very (relatively) thin sheet of rubber/sponge. Naturally this means that hardness number of topsheet will surely be dependent on hardness of sponge - after all almost as soon as the durometer starts pushing into the topsheet the sponge will come into play.   This seems to make the "topsheet" numbers very misleading then. The topsheet numbers would really be more of a "total hardness". Maybe if the table's columns were "with topsheet" and "sponge only" it would make more sense.

Added GD Karate Soft, Palio CJ8000 L&F, Donic Acuda S1 Turbo...

Added Gambler Outlaw Pro & Soft.

Also a couple of rather obvious (but still helpful) explanations should be made:

When the measurement is done, a pointy end of the device is being pushed into the material and material's resistance is measured. (Different scales even use different shapes - like hemisphere in one case, cone in another which makes these measurements completely independent meaning that there can be NO formula that transforms for instance ShoreA numbers into ShoreC numbers, only very approximate comparisons; that makes it important to use numbers from one scale ONLY; as well as not assigning them some magic properties which will allegedly tell you how the rubber will behave during the game; the measurements are "static").

That means that the material which is being measured MUST be relatively thick - otherwise you end up measuring the hardness of the table you put it on. That's why numbers that DHS, Butterfly and other manufacturers provide are so different from the ones we get when using durometers on a 2-mm thick layer of sponge (because they actually have layers of sponge which are foot thick or even thicker). Same goes for using durometer on a 4-mm thick rubber which consists of topsheet and sponge. The result (let's even forget about the table and assume it is always the same table) is naturally a mix of hardness of sponge and hardness of topsheet.

Let's take a look at the four Gambler Outlaw rubbers in my table - they all have the same topsheet but look at the durometer readings - it's 33 for Classic, 28 for GC and Pro, and 25 for Soft. Of course the hardness of the topsheet is about the same for all four of them - probably somewhere in the neighborhood of 28-29. But when we measure hardness of Outlaw Soft from topsheet side we get sponge's hardness (which is quite low) mixed up into the topsheet's hardness.

So there should be a formula that goes like this

Measured Hardness of T/S = W x Actual Hardness of T/S + (1-W) x Actual Hardness of S/T

where W is a number (weight ratio) between 0 and 1 which shows how exactly we mix together hardness of topsheet and sponge to get the "measured" number. T/S means "topsheet/or/sponge" and S/T means "sponge/or/topsheet".

I am not an expert on hardness-elasticity theory and cannot compute more or less reliable value of that coefficient weight W, but it has to be more than 0.5, probably much closer to 1. Let's assume that it is 0.75 (nice number taken directly from my imagination; it could be 0.86110293 for all we know).

That means that for Outlaw Pro 28 is indeed more or less "real" hardness for both topsheet and sponge.

For Outlaw Soft we thus get

21 (Measured Hardness of Sponge) = 0.75 * (Actual HoS) + 0.25 * 28 (Actual HoT)

which gives us Actual HoS around 18-19 (or approximately 27 on DHS scale). Looks a bit low but then again, it could be true. Or a whole load of bunk. Either way, try it out.

I agree - the durometer readings should only be used for comparison and only when done with the same durometer, at the same place, using same method (like testing rubber in six random points then averaging it out). BTW, good (for our purpose) durometers use hemisphere as the probing shape, not the sharp point (those are better for really hard things like metal, rocks and plastics)