Updating the Calibration List

[Guest Luke Reimer]

StrongerthanArne brought up a good point about the calibration list. I was thinking the same thing--the gripper calibration thread needs to be updated to specify handle lengths. From here on out we are probably going to have lots of SOS grippers from PDA--all with identical handle lengths--starting to hit the calibration list. For the calibration thread this means that it will only be necessary to specify handle lengths for specimens departing from the norm set by PDA (which we shall know). What do you say, Wannagrip?

[Bill Piche]

I view that thread as merely an FYI for info only and not some official "list".  

So, it makes no sense to me to add handle lengths especially given measurement errors and the like by the guys measuring them.

The IGC will have an official list which will obviously account for such variables.

[Guest StrongerthanArne]

Naughty, naughty Wannagrip. Be nice. ...make no sense... can easily be interpreted as ..... crawl back to the hole from where you came.... Of course it makes some sense. What is your point of having the list at all when we know that we cannot compare inch pounds figures unless the grippers have the same length.

[Bill Piche]

Naughty?  I would suggest you quit reading emotion into my posts.  I was just stating my opinion.  No emotion involved.

The IP ratings are still at the same place.  It never was intended as an official list. It was for info only. Like I said, the IGC can do all the official stuff and I am sure Tom will be supurb at these details.

Therefore, since it now seems to be causing confusion, I will no longer be updating that thread.

[Tom Black]

I think we may be jumping the gun here.  It seems to me that the SOS Press may be able to measure the differences in grippers caused by differences in lengths.  If this were not the case, why then did the only Master tested and reported read 330 inch-pounds?  This is much higher than any #2 gripper.  My particular Master gripper has a shorter overall length than my #2.  Shorter gripper, same spring, higher included angle, hence stronger gripper.  The Press detects the obvious difference between the grippers.  

My point here is that if your gripper is shorter than another  with the same characteristics held constant then it would already be reflected in the inch-pound reading.  I’d like to see PDA test a gripper and then begin to file down the handles, measuring it every 1/16”.  I believe that I know how to calculate the difference in the gripper torque and would be interested to see if the press gives the same readings.  

[Guest Luke Reimer]

Wannagrip, the only reason that the calibration list is causing confusion is that its information is incomplete. If handle lengths were added, then I think it would nolonger be the fault of the thread if people remained confused. For the sake of readers that don't wish to calculate equivelencies, a disclaimer could be added to the top of the thead, cautioning that spring ratings cannot be compared between grippers possessing different handle lengths. In this way the list would still enable everyone to compare some entries (eventually), while others of us would know how to compare any two grippers.

Of course this doesn't work unless the handle measurements come from PDA. I was under the impression that PDA was gathering such information. Isn't that true?

It only makes no sense to add information about handle lengths to the calibration thread if you have already decided that the thread cannot be salvaged and therefore has to be scrapped.  I would be sorry to see the thread lost unless there's nothing that can be done for it.  

Conversely, I think it makes no sense _not_ to add handle lengths if we were to keep the thread going.

[Guest Luke Reimer]

Tom, inch-pound ratings (such as 330 inch pounds for the BB Master you mentioned) are strictly spring ratings. They don't say anything about the rest of the gripping apparatus. If there is a Master rated at 330 inch-pounds, then its spring really is stronger than the spring found in most (or all) IronMind #2s. How could this happen? I guess anything's possible with the prevailing quality control.

From what I understand, PDA's machine cannot tell the difference between grippers with the same spring strength but different handles lengths, because it holds every gripper the same distance from the spring. If I'm not mistaken it applies its force to the handle at a point exactly 2.375 inches away from the spring. In this way the machine cannot tell the difference between two different handles, or even the same handles before and after modification--because it always takes an extremely low grip on the handles.

I know I'm probably being painfully redundant, but I think the easiest way to make sense of everything is to remember that IP ratings are only spring ratings. The only way spring ratings can become a stand-alone rating system, and thus a basis for overall comparisons, is if all other gripper variables (mainly handle lengths) are held constant. Otherwise, we either have to refrain from comparing grippers of different dimentions, or get the extra information and do the necessary math.

[Bill Piche]

Luke, if you want to take over the thread and update it, go right ahead.  Just cut and paste it into a new post and then edit it each time. You must add a post to it as well to bounce it to the top of the board.

May the Force Be With You. :biggrin:

[Guest StrongerthanArne]

Well said, Luke. Tom , as an example I could mention that a friend of mine is able to do around 15 repetitions with a 286 ip CoC #2. He tried my (now to be returned, see John's previous thread) 330 ip SOS gripper and managed none. The SOS gripper is 2.5 mm shorter than the 286 ip CoC #2 so the feeling of the 330 ip gripper would be more like 340 ip or so, using the 286 ip gripper as standard.

[MilGrip]

I hope it's not just me, but I seem a bit perplexed by this thread. As Tom stated, in the measuring of various grippers on the SOS gripper calibration scale, the handle length of the given gripper is taken into acount at the time of its measurement. The coil is the fulcrum and the point at which pressure is applied to the gripper is determined by the handle length of said gripper, right? How could one possibly say that one gripper is NOT harder to close than the other even though its closure in-lb wise, has been determined to be as such in relation to the other gripper, simply because one of them has a shorter handle? These measurements may not be taken under the most stringent laboratory conditions, but they seem fairly accurate to me, considering the nature of the grippers being tested. It seems Mr Black has quite a task at hand in quelling or allaying the fears and or concerns of us who are so grip obsessed and finicky about the conditions and methodologies by which our precious tools of the trade are quantified.

M Bolstad

...if you're gonna do it, over do it.

[Roark]

If the devil is in the details, there must be

Satan sightings all over this board!

Seems like we are planning the fun right out

of this whole situation.

If each contestant uses the very same gripper

in a contest aren't some of these issues beside

the point? Perhaps a grip machine would be a

better solution at contest time?

[Guest Luke Reimer]

MilGrip,

1. Regarding the interaction between the testing machine and the grippers to be tested, you suggested:

"The coil is the fulcrum and the point at which the pressure is applied to the gripper is determined by the handle length of the said gripper, right?"

Wrong. The point where the pressure is applied to the gripper is not determined by the length of the  handles. It's determined by where the machine loads the handles. Actually the spot the machine presses on is nowhere close to the end (it's only 2 3/8 of an inch from the spring end).

2. The tricky thing about understanding grippers is that there are two different values that have to be  kept straight. There is the value of the spring itself (this does not change) and there is the value of the  force required to overcome it (this changes according to handle length).

A spring has a certain built-in stiffness that never changes (or hopefully doesn't change much), no matter how you try to overcome it. You can overcome the spring's innate stiffness more easily by using a longer handle, or less easily by using a shorter handle--but you are not changing the spring itself.

It so happens that there is a special unit of measure for describing the built-in toughness of the spring (i.e. the coil) itself. This unit would be inch-pounds. Once you are into inch-pound values, you are  talking about the spring only. And once you have an inch-pound value for a spring, you have a value  that does not change unless the spring breaks (whether it breaks all at once or in degrees).

You cannot change the inch-pound value for a spring merely by measuring the spring from a different distance. The spring is still the same spring, regardless of what you attach it to.  You can measure its  qualities by using a big force from a short distance, or by using a little force from a long distance.  Either way the product will come out the same once you multiply the two numbers (i.e. the inch  value, and pound value) together. The product of 100 pounds from 5 inches, comes out the same as 5 pounds from 100 inches. If you take a gripper with a spring rated 500 inch-pounds, there is no way you could find a different number for that spring (in principle, and barring extremes that change the quality of the spring itself, or the degree to which you are overcoming it.)

A gripper with a higher IP value is a gripper with a tougher spring. That does not mean that it is actually harder to close. All other things being equal, the gripper with the hardest spring will be the hardest to close. However, IP ratings do not describe all other things; they only describe the spring's built in toughness.

Spring ratings will eventually become more generally synonymous with difficulty ratings (the two are not the same thing) once the leverage variable is nailed down by tighter (manufacturing) controls on the handles.

Clear as mud?

[Guest Luke Reimer]

Roark, what's wrong with using grippers in competition? If each contestant uses the same gripper in competition (or even two different grippers with identical dimentions and spring ratings, thanks to PDA) what would possibly hinder us from comparing the achievements of the participants using them?

One thing grippers seem to have going for them is that they are the ultimate cheat busters. So far every known machine (as far as I have seen) for simulating grippers can do no better than seek to minimize the effectiveness of cheating, and recommend disqualification when it happens. With grippers, after the initial set, your four fingers are pretty much on their own with no hope of help from anywhere else. If you want a contest for isolating crushing power, grippers still look promising to me.

[Guest Luke Reimer]

Wannagrip, I'll consider updating the callibration thread if I can find some PDA's measurements. Of course, if this becomes anything like hard work, then I can't promise anything. What was that closing comment you made to me? May the Farce be with me? Oh, oh--sorry--"Force."

Cheers,

Luke

[Guest StrongerthanArne]

Just a couple of comments to Luke's excellent explanations.

Luke wrote: It so happens that there is a special unit of measure for describing the built-in toughness of the spring (i.e. the coil) itself. This unit would be inch-pounds. Once you are into inch-pound values, you are  talking about the spring only. And once you have an inch-pound value for a spring, you have a value  that does not change unless the spring breaks (whether it breaks all at once or in degrees).

In an attempt to make thing possibly easier to understand, I would add that the inch-pound value is not constant for a spring as is it depends on which handles are used when the measurement is taken. For example, if a gripper turned out to give a 400 ip reading and we then shortened the handles by 5 mm then we would get a different, higher inch-pounds value because the shorter handles would allow the spring to compress more. The 5 mm shorter handles would give the feel of approximately a 420 ip gripper using the 400 as standard, BUT on top of that the 400 can no longer be used as standard as the spring is now compressed more and will yield a higher inch-pound value.

Luke wrote: A gripper with a higher IP value is a gripper with a tougher spring.

Shorten the handles and the spring will yield a new and higher inch-pound value as it will compress a bit more.

Luke wrote:However, IP ratings do not describe all other things; they only describe the spring's built in toughness.

I would add: the IP rating gives a value that is only valid for the spring when it is used with the original handles since PDS's machine gives the reading when the tips of of the handles are just about to touch. Shorten them and the spring will compress more and the reading will be higher.

Cheers

[Guest Luke Reimer]

StrongerthanArne, is right, of course. I was seeking to get strictly at the principles that were being misunderstood, and was intentionally ignoring or parenthetically minimizing other factors.

[Bill Piche]

I was laughing cause I typed that and then realized again your name was LUKE.  HAHAHA!  So, it really fit:

May the Force be With You Young Skywalker.

[MilGrip]

Luke,

I do understand how the spring is the biggest variable in the closure force of the grippers, I just hadn't realized that the handle size was not taken into account. Thanks for the clarification. It seems there may be a few subtle, albeit significant weaknesses in the SOS calibration press (No offense by any means John). I do think however that it is the most reliable way of gauging the strength of the known grippers.  I too am intending on sending my grippers to PDA, but a combination of not wanting to let them go yet, and procrastination has stalled me.  I'll post the results to add to the ever growing pool of gripper ratings when it comes that time.

M Bolstad

...if you're gonna do it, over do it.

[Guest Luke Reimer]

MilGrip,

Actually, I cannot conceive of any weakness within the SOS calibration system itself. If you want a measurement that *directly* describes the minimum difficulty of closing a given gripper, then you cannot talk inch-pounds values anymore.  Inches times pounds makes a special unit that describes only the internal properties of a spring (the so-called spring constant). This limitation does not arise merely because of the way PDA uses these values–there is simply no other way to use them. If you want to talk *directly* about the force of closing the grippers, then you have to go back to using values that are in pounds. The reason we have been getting away from that measurement is because it’s so slippery.  Any given gripper has not merely one value in pounds, not merely ten, not twenty, but an infinite number of them, depending on where this gripper is held. Which pounds value do you choose? You could choose the one you get by measuring at the end of the handle, and ignore the other values. Then indeed you would have only one pounds value for each gripper (this would be the theoretical minimum pounds value). There’s just one little problem. No one ever experiences that particular pounds value, because its impossible for anyone to use the grippers that way (Of course the human hand cannot bring all its force to bear on one small point, but rather must bring its force to bear over a broad range). Now what do you do? You’ve found a way of assigning pounds values uniformly, but now the measured values will always be lower than the practical ones, i.e. the ones applicable to the human hand. So what do you do? You could try  to make sense of your measured pounds values by saying that they were only meant as relative scores, not literal pound values. But then what’s the good of using them? If we aren’t actually describing how many pounds the human hand feels (this would be hard to figure out), then why bother creating the illusion that we are doing this?  The alternative, of course, is to use a more abstract score that applies only to the springs (in inch pounds), and then sit back and hope for the day when gripper dimensions become uniform, so that we can compare spring scores directly and easily, without the necessity of making mathematical adjustments. So far PDA is the only company seeking to make this dream happen.  It’s not PDA’s fault (and I don’t mean that you were saying so) that the grippers we have inherited from yesterday are slightly difficult to compare with each other–much less compare with any gripper PDA might build. If it were up to PDA alone, our grippers would conform to much tighter specifications, and we could compare ratings straight-across without even stopping to think. As things are, we’ll just have to be a little more careful with our comparisons.

Good decision to send your grippers in for testing! I had trouble letting go of mine too. (Now that their gone, I’ve been pounding my hands harder with thick-handled snatches and cleans to make up for it. Soon I should have my Ivanko SuperGripper to tide me over) Yes, do keep us updated!