Vic 111mm Backside Phillips is PANTS!! (that's bad...)

[Dunc]

I too have never seen one of these break  I've never been a fan of this phillips and would always favour the one on my plier based multitool . I do however prefer my 111mm to have a corkscrew 

Dunc

[Mr. Whippy]

What would constitute a failure though?  How much torque should it cope with?

Well, in general, T-handled drivers are for high torque situations when the user wishes to apply more force to torque and less force to gripping the driver handle (increasing the frictional force to the driver handle).

I don't know the actual failure torque value for a standard T-handle driver.  I can tell you, from my experience using torque wrenches, the failure in this case was well under the 30 Nm of a M10 frame bolt.


Using a thought experiment, if the outer liner was aluminum foil, and the pin was HighTorqium, the liner would immediately fail on torquing.  (ie the liner wouldn't be able to retain the driver)

If the liner were made of thin aluminum and the pin were made of unbreakable String cheese, the pin would stretch, but only after the liner started to deform. If you change out the pin to HighTorquim again, the driver would start to rotate, but only as much as the liner would deform. At high enough torque, the liner would rip out at the hole just as the aluminum foil does.  Make the liner twice as thick, and the deformation requires higher and higher torque values.  Make the liner out of inch thick HighTorquim and the driver failure only occurs when the Phillips head twists off.

If the liner were again made of High Torquim and the pin were made of uncooked spaghetti, the driver would rotate and snap the spaghetti, but only if there is enough space that the driver can start to rotate.  If clearance is 0 and the liners immovable, the pin receives none of the torque, with all of the torque applied between the corners of the tool and the adjacent liners.

Anyone who has worked with the liners knows they deform very easily.  This leads me to believe that the outer liner deformed enough to allow torque to be delivered in significant amounts to the brass pin. Remember, this tool was modded a year ago and has been used since then.  The repeated application of torque to the soft brass pin led to deformation and eventual failure.  I believe any backside driver would suffer the same fate since the liner in any case will suffer deformation with high torque and will lead to shearing forces on the brass.

But that's just my theory.

[Benner]

But are we to treat that driver the same as a T-driver?  Are we really to expect the same performance out of a 111mm SAK as the "real deal"?  (I'm just stirring it now  )

[Mr. Whippy]

But are we to treat that driver the same as a T-driver?  Are we really to expect the same performance out of a 111mm SAK as the "real deal"?  (I'm just stirring it now  )

That's wot it looks like...

Are you proposing a poser Victorinox tool!

[Neil]

I've never come across any SAK however abused that has a snapped pin.  So this is really weird.  I've seen deformed liners before but on corkscrew SAKs.  These normally have bent corkscrews as well.  I've seen older SAKs where every liner has split in two!  but even then the pins were all OK.  Its proper bizarre 

[Benner]

But are we to treat that driver the same as a T-driver?  Are we really to expect the same performance out of a 111mm SAK as the "real deal"?  (I'm just stirring it now  )

That's wot it looks like...

Are you proposing a poser Victorinox tool!

Not at all (and you know it    ) but are we really to expect that level of performance out of a SAK?  Surely we need some level of sacrifice for the sheer amount of function we have in such a small package, perhaps ultimate strength is that sacrifice?

[nuphoria]

Cor blimey  

I've never come close to messing up a Vic like that - I think Mr W must have very big butch hands!



Whether the tools should be expected to deal with such high torque is a goods question - should we asking someone from Victorinox this?

[tim]

What would constitute a failure though?  How much torque should it cope with?

My point is that the first effect of over-stressing the philips is to stretch the brass pin holding the knife together.  Using the bottle-opener as a lever would have a similar effect.  And once the pin-head fails, the liner and pin-shaft will inevitably cede.

Now this is a modified knife: the part which is critical to the integrity of the knife against transverse forces -- the pin heads -- is exactly the part which has been  re-worked.  Mr. Whippy's breakage may be due to the fact that it's difficult to re-make the brass pin-heads to the same strength as the original.

With brass being as soft as it is, I'm surprised not to see more of this kind of thing. 

[Neil]

It appears to be a shear of the brass though, not the head?

[tim]

As long as the pin is tight, the screwdriver is twisting against the liners and not the pin itself.  As soon as the pin lets go of the bushes holding the knife together, the liners move apart (as in the photo) and the screwdriver is twisting against the pin.  At this point the knife is doomed: the screwdriver is now twisting directly against the thin, soft brass pin, which is likely to fail immediately.

The pin head must have failed first, before the body of the pin was sheared through.  If the pin head had not failed, I guess the knife would have held together.

I can't claim the modified knife was weaker in this respect than an ordinary model, but it's a possibility.

[Mr. Whippy]

Science!

It's the only way.  I didn't have another 111 mm to use as an experiment so I picked out this 2 layer 91 mm SAK.

Here are the testing gear:  NE size socket, SAK, Torque wrench:


I placed the SAK in the Vise so that the edge of the tool is free, that way the vise isn't acting as outer liners:


Long story short, I don't have an inch-pounds torque wrench.  The tool failed at less than 10 Nm! 


The failure appears to be EXACTLY the same mode as my 111 mm SAK. The Brass was cut through when the liners gave way.


Conclusion:

The backside Victorinox Phillips is in NO WAY to be confused with a T handle driver. Best used for pre-loosened screws.

[Benner]

See, I don't see it as a T-driver.  I just see it as a driver hanging off the back of a backspring.

I doubt any of it is as strong as the "real deal" but that's the price you pay for compactness and the range of tools it offers.

Question is, is 10 NM the same as that of the 111mm SAK?

[Mr. Whippy]

Less than 10 Nm.

10 Nm is about what an oil drain plug is torqued.  Really not much. This Phillips can't really be trusted to remove anything of a mechanical nature. Trim pieces, electronics screws and maybe some wood screws.  That's about it.


Again, not a real Farm EDC tool. 

[jzmtl]

Well to be honest how strong did you expected it to be? Brass is as soft as it gets, not even mild steel can be peened the way brass pin is, let along compare with heat treated tool steel used in real drivers.

MT just aren't made for high stress uses, I remember a guy used his wave bit driver in 90° position to get more torque and shattered the bit holder.

[Sea Monster]

Following your lecture on Engineering (and home cooking) two of my favourite subjects, as it turns out, but that's another matter.

It could be that after the mod the distances between tool shank and liner were ever so slightly increased allowing some rotation of the Driver, contributing to (if not the sole cause of) the failure of the pin.


I'm not saying it wouldn't have broken anyway, as the nutter with the torque wrench indicates, just that it might have helped.

[Turnstone]

Thanks for these interesting insights!!! I just love my Trailmaster, and I love having a phillips driver on it. Now I know that I have to be careful with it. I used it once with quite loose screws on a geocache, and I wanted the phillips driver for exactly such applications. But you newer know when you need one and have nothing but your SAK with you... now I know that I don't want to use it for reall heavy use 

[ICanFixThat]

..... now I know that I don't want to use it for reall heavy use 

Or you could say you know to clamp the vice grips in the center of the knife and use them as a lever for those heavy use jobs.   

I hope every one realizes that Torque and Phillips never did get along regardless of the driver.

[J-sews]

How much more torque would it be able to stand if the pivot area of the phillips (where the hole goes through) were made square, instead of round?

[Mr. Whippy]

Dunno...

I don't know really what it would take in torque.  I don't have an in-lbs torque wrench.

[cannonball]

I've always lived by the rule only to use SAK tools (except for the knife blades) when a dedicated tool is not available. I've always felt the back side driver pin is too small in diameter.

[John]

I'm wondering now if the hook can really carry 250lb with a jolt? that's a lot of force on such a thin pin

[Sea Monster]

I don't have an in-lbs torque wrench

For those of us in....well, everywhere else in the world, what's the benefit of in-lbs over N.m?

[Mr. Whippy]

I don't have an in-lbs torque wrench

For those of us in....well, everywhere else in the world, what's the benefit of in-lbs over N.m?

ft lbs about 25% more than Nm.  An in lbs torque wrench is for tiny torque measurements (because an inch is 1/12th of a foot). 

1 N m = approximately 0.75 ft lbs

1 Nm  = approximately 9 in lbs.

My torque wrenches are for mechanics (cars, tractors and motorcycles) I have no need for in lb torque wrenches

[DaveK]

I don't have an in-lbs torque wrench

For those of us in....well, everywhere else in the world, what's the benefit of in-lbs over N.m?

ft lbs about 25% more than Nm.  An in lbs torque wrench is for tiny torque measurements (because an inch is 1/12th of a foot). 

1 N m = approximately 0.75 ft lbs

1 Nm  = approximately 9 in lbs.

My torque wrenches are for mechanics (cars, tractors and motorcycles) I have no need for in lb torque wrenches

You previously had no use for in lb torque wrenches. Now you need to get one. And smash up more stuff

[evil510]

I am hoping oversized stainless steel might help a bit. Especially if they go through the thickness of both scales as well....    (high grade aluminum alloy, haven't made them yet) At this stage of modding, fashioning new stainless steel liners would be easy enough to do as well.....

[Mr. Whippy]

We need to hear more about this one...

(I think a stainless steel liner on the Phillips side would help.)

[Sea Monster]

with some very dodgy, theroetical calculations, the hook on a backspring should take 250 lbs, (non shock load) before the pin fails.

Anyone got a sacriSAK and 250lbs to hang off it?

[jzmtl]

I just remembered something. I was using the awl on 91mm SAK to drill through eyes of a coconut, as it starts to penetrate the shell, I can feel the awl start to bind, and parts are flexing, I didn't apply a lot of torque to it, but I guess that's about all the stress aluminum/brass can take. Then again coconut shell is way harder than any wood I know.

[tim]

Hats off to Mr. W for carrying out that test. 
Now just a hundred or so more tests like that, on knives of various ages, and we should have some quite decent statistics. 

I've got to say in defence of Victorinox that 10Nm is quite a lot for a small screwdriver.  It's more than I can comfortably exert on a medium-sized screwdriver handle without using both hands.  It's also enough to properly tighten an M8 bolt, and enough to completely destroy an M5 bolt.