Closing torque

[Guest StrongerthanArne]

I have thinking a bit about grippers and in particular grippers with different handle lengths but with the same inch pounds numbers. Assume that we have two 400 ip grippers where one is 135 mm long (from the tip of the handle to the base of the spring and the other is 130 mm. If we set the 130 mm as standard what would the 135 mm one feel like closing? 130 divided by 135 times 400 is 385. Is it correct to measure the total length of the gripper in this case or would it be more relevant to take the measurements from the tip of the handle to the centre of the coil? Moreover, the 385 ip "feel" of the longer gripper would only be relevant if all force were to applied to the end of the handle when in fact it is distributed along much of the handle. For the pinky the difference would feel greater perhaps more like 80 divided by 85 times 400 = 376 ip. Does my reasoning make any sence or am I totally confused? Also, I have noticed that people with narrow hands do surprisingly well with grippers and this, if I have understood things correctly, would be due to the fact the the centre of the force applied would be further away from the coil than with a broad hand. Any thoughts?

[Guest Youngguy]

You make alot of sense. The handle lenght is a huge part of the torque. This is what is called leverage. Take the same princible with nails. Longer the nail is usly depicts the strength needed to bend it. That is why people like John Brookfield cut the nail down to size to make it alot more tougher. If you already know all this well im sorry, but I tried to help.

[Guest Youngguy]

You make alot of sense. The handle lenght is a huge part of the torque. This is what is called leverage. Take the same princible with nails. Longer the nail is usly depicts the strength needed to bend it. That is why people like John Brookfield cut the nail down to size to make it alot more tougher. If you already know all this well im sorry, but I tried to help.

[Guest CalvinP]

I am not sure where on the hand the most force is exerted. Because by moving the hand away from the coil doesn't make it close any easier! It seems like you can feel it lighter, but you also have one less finger and palm to finish it into a click. Which is something I am still struggle with my #1 and my hands are small too, wish me luck next week.

[Guest StrongerthanArne]

I think you are misunderstanding me. Try closing the gripper with your pinky 10 mm away (inside) from the edge of the handle. I have noted on several occasions people with narrow hands doing surprisingly well with the grippers (with all their slim fingers cramped close to the edge of the handle for maximum leverage) but do poorly on other grip stuff, such as pinch and Rolling Thunder.

[Guest Luke Reimer]

StrongerthanArne--another good question! I've been pondering how to measure the handles too (I didn't mention this in other threads because I didn't want to complicate matters there).  Where do we interpret the "top" end of the gripper as being? I haven't really been schooled in the physics of torque springs, but my instincts had lead me to think that there would be two tops (one for each side) and that we could find either of them at a (possibly imaginary) point intersected by the line of the handle and a line perpendicular to the handle that runs through the very center of the coil. (Is this wrong, John. S?)  On the other hand, I get the impression that some are measuring simply from the far end of the coil. I'm not sure which is right, but I'm sure of this--there is a correct answer, and someone knows what it is and why it is.  Incidentally, the (bilateral) point I had in mind would be fairly close to the end of the gripper while it is in the open position (which is how we are measuring anyway, right?).  For any two grippers being compared, my way of measuring would result in a marginally larger rating adjustments to the gripper deemed different, than if the tops of the gripper were interpretted to be at the very end of their respective coils.

As for your other question about the perceived difficulty of two different grippers with the same spring rating (400 ip), but different handle lengths (135 mm and 130 mm), I have a comment. For the sake of argument, lets forget the measurement issue and assume that you measured the correct way (whichever way that would be). Based on your method of calculation (I never bothered to re-crunch your numbers), I agree that the adjusted  spring rating for the gripper with the longer handles would be 385 inch-pounds. What surprised me is your suggestion that it would not really feel this much easier.  Why not? You suggested that this proportionate increase in leverage could only be felt if, on the longer handles, you managed to deliver all the force of your hand to the very end of the handle. Why? Naturally it is impossible to apply all your force to the end of the handle, and you instead distribute your force along the handle to a great degree. However, this is just as true for the shorter handle as for the longer handle, and if you use the same technique on both grippers, the difference in where the force is distributed along the handles of the longer gripper and where it is distributed along the handles of the shorter one is proportionate to the difference in their spring ratings (after the adjusting calculation).  Did I understand you correctly?

By the way, I think you are right about people with narrower fingers having an advantage with torque grippers. I can't see any flaw in the reasoning that says the ability to gather your fingers further out on the handles can only help. (This would mean I am in luck, too, since my four fingers taper almost to 2.5 inches across at the tips, from palms 4.5 x 4.5, and rather thick. The downside of having this advantage, of course, is having one less excuse for being so thoroughly outclassed by our forum's champions.)

Cheers,

Luke

[Guest StrongerthanArne]

Luke,

No you misunderstood me (the second part), because I did not explain myself very clearly (used pinky when I ment the index finger). I ment that the longer gripper would have the feel of a 385 ip gripper if all force would be applied at the end of the gripper which , of course, it is not, but that at the level of the index finger the gripper would feel even easier to close since the torque arm from the centre of the coil (or top of the coil, whichever is the correct) is much shorter up to the centre of the index finger than it is all the way to the centre of the pinky (a 5 mm difference would make up a greater part of the 50 mm or so distance from the centre of the coil to the centre of the index finger than of the 100 mm or so distance from the coil to the centre of the little finger).

Cheers

[John Szimanski]

You've got the ball on this one folks. This may help (or not):

1. We measure IP from the centerline of the coil (as the gripper sits on the mandrel) to the point of contact 2-3/8" out on the handle (the midpoint of the floating way and clevis pin).

2. We are using an overall outside go/no-go fixture to set overall assembly length conformity within 1/16".  Our intention is that consistent configuration with 1/16" will essentially eliminate significant differences.

This is a pretty mired little mess. We're just going to minimize it in our grippers. I already have too many committments already to try to resolve a problem created by someone else. If you take it rationally, step-by-step, you will come to an acceptable solution. It need not be 100% precise, just reasonably acceptable? Don't forget, you also have a varying 45 degree bevel in the works, too. Don't chase yourself forever. If you feel you're defining it within 2%, be satisfied.

Or, you could ask Strossen. ?

John

[Guest Luke Reimer]

StrongerthanArne, about comparing gripper difficulties between grippers with different handles, I get your point this time.  Your argument was a good one and its sophistication went right by me initially. Now I'm embarrassed by my ludicrously simple characterization of it.

The calculations I suggested for finding the relative difficulty between grippers with unlike handle lengths requires getting a (precise?) measurement of the total handle length of each gripper. You identified two difficulties of getting even a basic measurement, only one of which difficulties I had ever thought about on my own. The second one went over my head the first time.

The first difficulty was this: where do we find the top end of the gripper?  This is not quite as easy as looking at a prybar under a load, and saying the end is where the load touches the bar.  With the gripper the load is somewhat internal, i.e. enclosed within coils that are visually continuous with the handle. Where does the handle end and the load begin exactly? I ventured a guess but that was all. (I still think there is single correct answere here, but it may involve a deeper understanding of math or physics than I had supposed).

Your other question suggested that not only do we have the difficulty of locating the spring end of the gripper, but that of locating the handle end. Where does the handle really end? We can easily enough see the end of the aliminum handle. But is the phyisical end and the functional one the same thing? Given the way the human hand uses the gripper? Apparently not. The balance of force, if we were to take some sort of weighted average of all the tactile pressures coming into play, would probably be represented at a point along the handle somewhat inward from the physical end. I have no idea how anyone would find this point.

Unfortunately, it would seem that if we cannot find either end of the gripper, then we certainly cannot write a fraction expressing the difference between the lengths of two grippers, and use this fraction to calculate a difficulty adjustment. We could still do this using the measurements we were using before, but our numbers would be off somewhat, and this would deflate our ratings adjustments by some percent.

I still see no harm in using these calculations to get a rough impression of what someone is doing with another gripper, or even to help you figure out what SOS grippers to buy next.  

On the other hand, at this point I have to concede that my earlier indifference to the issue of quality control was unwarrented. I was mistaken. We think we cannot be content to have grippers made in any old dimensions, and then try to make good comparisons on the basis of math and linear measurements.  It would seem our best hope of making any reliable comparisons between grippers lies in keeping the dimentions uniform through better quality control.  

John Szimanski, Wannagrip, you were right all along!

Cheers,

Luke

[Guest StrongerthanArne]

Hold on Luke,

Don't give up so easily. Let's use mine and Arne's recently calibrated IM grippers as an example. His #2 and #3 are of the same length and the inch pounds numbers are thus directly comparable from a "difficulty to close the gripper" point of view. His #2 is 286 ip, whereas his #3 is 410 ip. My #3 is 396 ip but is 2mm longer. The centre of my index finger gives a torque arm of about 50 mm, whereas the centre of my little finger (basically the end of the handle) gives 110 mm. If we use an "averaged" torque arm of 80 mm my gripper would have the feel of a 386 ip gripper (using Arne's two as standard). If the torque arm instead is set at 70 mm we would get 385 ip, so this method is rather robust and gives a reasonably constant result even given the differences in the width of peoples hands.

Cheers

[Guest Luke Reimer]

Michael (anyone else, you may not enjoy this as much) this is really interesting! I had just assumed that in measuring the functional handle length, picking the wrong reference points for the measurements would affect the ratings-adjustment calculation severely. However, a measurement error that causes the ratings adjustment to be off by only one IP unit would not seem to be half bad, especially if the chosen reference points were a whole centimetre away from the correct ones.

I want to go over your measurement examples again. Thus for two given grippers, we have one way of measuring that finds them 80 and 82 mm, respectively, and the another way other gets 70 and 72 mm. These methods differ by a whole 10 mm, and yet when we take quotients from each of these pairs, they yield multipliers that are extremely close--within 1/3 of a percent of each other.  For a 396 inch-pound spring, the adjusted rating would be 386.3 or 384.9 Ips respectively–almost within one point of each other. Nice find!

Apparently it helps that the grippers you selected were so close to the same length (within 2 mm). Clearly the measuring methodology–as long as you used the same method for any two grippers being compared–matters less and less the more similar their handle lengths are. For example, if their handle lengths were the same, then any method of measuring at all would work as long as it reflected this sameness. Whether you measure them as 80 and 80 mm, or 70 and 70mm, the quotients from these separate pairs will be identical, each resulting in an adjustment by a multiplier of “1"–which means no adjustment at all (which is as should be).

Now if the reference points chosen for measuring the handles do not change the ratings-adjustment calculations at all when grippers are the same length, and change them only slightly when the grippers are nearly the same length, then what about when comparing grippers with lengths that are less and less similar?  Instead of two sets of handles that are only 2 mm apart, consider some that are 10 mm apart. (And lets keep assuming your gripper is the longer one). Now after you crunch the numbers, the two example methods are within 1.3 percent of each other (adjusting your spring rating to 352 IP or 346.5 IP). This means the calculations are within 5.5 points of each other; that’s not fantastic, but then again, not terrible either. If we then move to grippers that are 20 mm apart and  measure them one way as 80 mm and 100 mm respectively, and another way as 70 mm and 90 mm respectively, we now have quotients that are about 3.2 percent away from each other (within about 9 points on your gripper, i.e. 317 and 308 adjusted IPs). The best news here is that the chances of finding grippers with handles differing by much over 1 cm (and these calculations out by more than 1.3 percent) are probably relatively low.

So once we are dealing with grippers whose handles vary too much in length, the only way we could calculate a ratings-adjustment to any reasonable percentage of accuracy would be to know exactly the right way to measure the functional handle length. On the other hand, the smaller the difference between the gripper handles, the less necessary that it becomes to choose the correct reference points for measurement, so long as the same reference points are chosen on each gripper.

I was intrigued with your latest proposal in the way of measuring methodology. Measuring the total length of the gripper first from the pinky-finger perspective and then again from the middle-finger perspective, and then taking the average of the two lengths would indeed seem to put us closer to the true functional length than if we just took the total physical length and ignored every other length at which force were being delivered from the hand to the gripper. I would guess that  for most hands (on any given gripper) the overall forces from the hand necessary to close the gripper would correspond roughly to a single force necessary to close the gripper from a point ranging somewhere from the centre of the ring finger to the side of it nearest the middle finger. Actually this reference point would probably be similar to the one resulting from your way of measuring by averaging the lengths at the ring and index fingers.

What does all this mean? I think that at the very least we may have an fine mathematical basis for making informal comparisons between grippers of different lengths, even if we never figure out exactly the right way of measuring. In fact, if the grippers under consideration have handle lengths within a few millimetres of each other, we may be able to calculate ratings adjustments that are accurate to within a single IP point. On the other hand, for the most stringent comparisons we probably have to restrict ourselves to grippers possessing uniform dimensions. Thanks goodness for some new quality control!

[Guest StrongerthanArne]

Luke (and others interested),

I doubt that the vast majority of IM grippers vary more than 5 mm in handle length, so the problem arising from grippers with very different handle lengths is probably only a theoretical one (I am here assuming that there will be very few on the list certified on a gripper other than those of IM and PDA). In the upcomming Löddeköpinge Grip Challenge II, we are going to use the three gripper just mentioned and my 396 IP #3 will be given a 386 IP "difficulty to close" rating (subjected to possible adjustments pending more accurate measurements taken with a caliper) so that it can be readily compared to Arne's shorter 410 and 286. We also hope to add three SOS grippers ordered at 300, 330, 360 IP. Should these differ in handle length from the 286 and 410 IM grippers then I will simply give the IM a new "difficulty to close" IP rating. It will take less than a minute and we will be ready to compete. We are going to add the IP numbers for the right and left hand to yield a combined total IP figure (no hiding for a weak left). Based on my own more or less suspect calculations I estimate that I am currently good for about 375 IP with my right and 325 IP with my left (both figures with Arne's 134.5 mm 410 and 286 as standard). I will soon start to do heavy singels as the competition approaches. Like you I have rather slim fingers which gives me an advantage with grippers but a disadvantage with pinching I would guess.