Gerber Dime design problem

[ioti]

Before buying a dime I did my due research about it and found many instances of its scales bending. When I received it, the quality of it was impressive, I had a good one turns out. I started wondering why it has a tendency to bend and it did not take too much time to notice this:


As can be seen one side is 2.5 to 3 times thicker than the other. Moreover thicker side has a steel liner which further increases the stiffness and strength. Thin side is slightly thicker than a beverage can and cannot be expected to bear any load really. I like the tool generally and am planning to replace the thin scales with probably carbon fiber (I have some sheets laying around)

[Vidar]

I started wondering why it has a tendency to bend...

You bend handle itself? Or just the aluminium covers? Or does it bend in the hinge from handles to the pliers when using the pliers? I am not able to bend anything on my Dimes actual handle, but I can bend both things mentioned before. It doesn't interfere with any functionality though.

Thin side is slightly thicker than a beverage can and cannot be expected to bear any load really.

It doesn't seem to have any structural purpose - it looks to be just a cover. The main structure is in the middle on both sides of the pliers.

(As a sidenote it actually does have a bit of load bearing ability too. It just depends on the load direction. I would expect it to stay very straight and take a fair bit of load in a tensile stretch scenario for instance. But again, looks like just a cover).

[gerleatherberman]

Wouldn't worry too much about it, since they are usually less than $20 and Gerber will replace it for free(well...the cost of shipping one way) if it fails. But, that's just my opinion and mileage varies.

Lots of Dime owners have carried theirs for years without issue, and some have had issues out of the box. Just something inherent to budget tools.

Would love to see your CF mod once you finish it, ioti.

[Vidar]

Lots of Dime owners have carried theirs for years without issue, and some have had issues out of the box. Just something inherent to budget tools.

Yes, there is that of course - some are just a bit off.

Would love to see your CF mod once you finish it, ioti.

+1 to that. 

[ioti]

Vidar, I didn't bend it, just saw cases of the scale bending in the internet. What happens is people use the screw driver heads to pry open something and the scales give away. And it is said to happen at very low loads. So there is definitely room for improvement.

[Vidar]

Ah. Well, that makes sense.

The Dime is a keychain tool though, and not very expensive at that, so I assume weight and price has been key design criteria. It has other flaws as well, but for the weight it is pretty much what I expect - actually pretty good overall, and very likable. A larger diameter/stronger pin would have helped with that issue though and not added much weight.

I guess for me the key questions are if the scrrwdriver performs as one can expect (ie not due to some artificial destructive testing), and whether it takes damage or returns back to normal afterwards. Hm. I might have to give it a try. 

[Vidar]

As what I really should be doing got real tedious I figured I'd open a Gerber Dime instead. This thread got me interested in the pin dimensions and material.

(If twisting the screwdriver causes issues the culprit is likely the pin stretching and then bending. If the pin doesn't stretch then the pin head should keep it clamped in place regardless of the cover thickness. The cover is just fastened one other place and thus will likely just hinge outwards regardless of its thickness. But it can't hinge anywhere if the pin doesn't stretch).

First thing to notice on the Dime was that it is not riveted like say Victorinox SAKs. It is a hollow pin with internal threads for two screws - one from each side. Inside threads in a roughly 2.9 mm pin means the screw will be tiny - and it was. It measures about 1.8mm diameter, which after subracting threads means that the non thread center is just around 1.45mm or thereabouts. That isn't all that much material, just 1.65mm2 area, and I imagine prying with a screwdriver can stretch that.

That good news is that one can replace that assembly with a riveted solution like Victorinox uses, and a roughly 2.9mm pin (I guess some round inch measure?) will give about 6.5mm2 of material area instead. That will be around 4 times as difficult to stretch.

Ok, how do I get this thing back together? There seems to be too many parts already? 

[RF52]

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[ioti]

Interesting Vidar. Regardless I am still planning to replace the scales. Stiffness can be increased by scales and/or pins, so making either more solid would increase the rigidity of the whole thing. What size torx screw are those? The ones I have have tend to slip from Dimes screws.

[Vidar]

Interesting Vidar. Regardless I am still planning to replace the scales. Stiffness can be increased by scales and/or pins, so making either more solid would increase the rigidity of the whole thing. What size torx screw are those? The ones I have have tend to slip from Dimes screws.

The scale can be stiffer as such of course, so the handle would feel stiffer. My point was only that it wont help against the screwdriver twist issue - the screwdriver will still twist. (Just imagine the thing with infinitely stiff scales - it would still move outwards with screwdriver twist).

I'm actually not sure what size those are. I assumed something inch based, so for lack of that I just rammed some poor metric almost fitting one in there and hoped for the best    I'm sure someone here knows though. Anyone?

A carbon scale look should be interesting, so I'm hoping for pictures when you are done? 

 

[ioti]

I disagree with the twisting issue, I don't know if you are considering another mode of failure but the modes I have in mind will definitely benefit from scale stiffness. Nevermind, we are here for fun, I will definitely post the results here, the carbon fiber sheets are in my parents house in another city, will get them in a few weeks.

[Vidar]

I don't know if you are considering another mode of failure.

That might be? Ok, so this is what I'm considering. The first (rough) figure shows a thin bendable scale. When the screwdriver twist too much it is able to stretch the first pin, and the scale itself just bends away.

The second shows how the same will look with a stiff scale. The scale doesn't bend, and thus the second pin will also come into play. But because it is much further away the added leverage from the screwdriver twist will make it many times easier to also stretch the second pin (compared to the first that has already given in). Nor does the the second pin really need to be stretched much to give up space at the other end. Thus for all practical purposes this failure mode is next to independent of the scale stiffness.

Not that it really matters - plenty of other reasons to mod scales, and maybe the failure mode you think of was something entirely different. Will be interesting to see what you come up with.