I don't have any screws with such a ledge, and I do want flush engagement.Keep in mind that almost all screws have a slight ledge underneath. Typically you don't want the hex to sit flush with whatever is underneath. That does not completely clear most of the chamfers, but it does make its impact on how well the socket grips the screw head even smaller:
Also, if the screw has a standard washer underneath (not oversized), then I think all sockets fully come in contact with the head cause they can slide a bit further. That's why hex screws and hex nuts most commonly are used washers.
Why bother to make chamfer on sockets?
- Thread starter qqzj
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Are you sure? Maybe you never took a close look. The ledge is usually missing only on home-made screws that were turned on a lathe.
Why do you want flush engagement?
They are part of the imperial SAE standard:
As well as the European metric DIN standard:
And while the Japanese JIS standard hex bolts are a bit different and prefer to use flanged bolts, the flange design tapers down so the socket also sits further down, while the base footprint is circular:
The reason for the flange is not only to give more engagement with the socket, but to apply even pressure on whatever you're tightening. If the edges of the hex came in contact, that would throw off the torque, and they'd bite into material and tear it away, while also damaging the base of the hex screw head.
Every part of the screw has its reason to be there. If the ledge is part of practically all standards for screws, it is an extremely important detail.
Take a look, more specifically, at diagrams for sheet metal screws.
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Those ledges are not on sheet metal screws.
Those sheet metal screws hold about 5-10Nm, maybe 15Nm for really large diameters. Very low torque compared to a machine screw with the same hex head size. They go up to grade ~5.8, while nowadays it is hard to find a machine screw of a grade lower than 8.8 (much stronger material).
I doubt the socket can ever round off its head before it actually snaps off the stem of the screw if it is that incredibly stuck, no matter what kind of a chamfer the socket has.
Edit: for example, on google I found a table with the insertion and removal toque for 6mm, 8mm and 10mm (really huge) din7976 screws:
For a high tension M6, it's rated limit is already 20Nm. For an M10 it's over 90Nm... Totally different ballpark of torque. Even the regular 8.8 grade M6 is rated for twice as much torque as the ST6.
I doubt the socket can ever round off its head before it actually snaps off the stem of the screw if it is that incredibly stuck, no matter what kind of a chamfer the socket has.
Edit: for example, on google I found a table with the insertion and removal toque for 6mm, 8mm and 10mm (really huge) din7976 screws:
For a high tension M6, it's rated limit is already 20Nm. For an M10 it's over 90Nm... Totally different ballpark of torque. Even the regular 8.8 grade M6 is rated for twice as much torque as the ST6.
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I think when you twist a socket, the stress spirals from the square drive to the fastener head. The fastener head reacts that twist and by the time the spiral gets to the end of the socket, there's not much load left. The fastener has reacted that applied twisting load.
We know there is load and sockets are complicated. The tin walls don't react load as well as the meatier section between the square drive and the hex. Sockets go "out of round" so its not as easy as just a spiral. But I don't see a ton of load at the very end.
In bending members, the upper and lower chords see the highest stresses. In torsion, the outer diameter is where stress concentrates, not the inner. The outer radius may be more structurally important. Also, big size indicating numbers stamped into the side of the barrel would be undesirable stress risers. Note that Snap On has never done that to my knowledge.
We know there is load and sockets are complicated. The tin walls don't react load as well as the meatier section between the square drive and the hex. Sockets go "out of round" so its not as easy as just a spiral. But I don't see a ton of load at the very end.
In bending members, the upper and lower chords see the highest stresses. In torsion, the outer diameter is where stress concentrates, not the inner. The outer radius may be more structurally important. Also, big size indicating numbers stamped into the side of the barrel would be undesirable stress risers. Note that Snap On has never done that to my knowledge.
When you put force on a socket the screw is resisting the turning force (torque). Part of that force of the screw that resists turning wants to spread the socket apart. This is how sockets fail:
The force does not "come from the ratchet and into the bolt". That would mean the bolt spins completely freely. As long as there is any resistance, there is an equal reactive force coming from the screw - the force that resists the turning of the screw. So when you tighten a socket, every bit of it is under stress.
If the end of the socket had next to no stress, manufacturers would put a strong taper on them them, and that would allow you to reach tighter places with it. But that's not the case.
A force does not travel in that way. I tried to draw it, but I'm not the best at that. Look at what "enters" the socket. The moment/torque of the ratchet I marked Mr enters at the ratchet end. The reaction force of the bolt that does not move forms the Mb torque/moment.
The force does not "come from the ratchet and into the bolt". That would mean the bolt spins completely freely. As long as there is any resistance, there is an equal reactive force coming from the screw - the force that resists the turning of the screw. So when you tighten a socket, every bit of it is under stress.
If the end of the socket had next to no stress, manufacturers would put a strong taper on them them, and that would allow you to reach tighter places with it. But that's not the case.
rockettauto
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This is is why you won't normally find a chamferless socket meant for anything but low torque applications. Small screws and fork caps are typical intended use.
Chamfers are on every "normal" socket because they improve usability. The only time they don't improve usability, is when the chamfer takes away enough engagement surface to be noticeable.
Why this "could be noticeable", is simply a lesson better taught by experience.
But in general it shows up when there is a reduction from normal in engagement surface (ie a low profile fastener). When combined with high torque levesl, the reduction in surface area will concentrate forces of the tool in a smaller area, leading to a greater force/unit area.
Any time lack of engagement surface is causing problems, removing chamfers will always be an option to improve performance, because it adds-back engement surface.
Its never a zero-cost solution, because it causes its own tradeoffs.
A large enough force/unit area will -- at some stage--damage the fastener (lead to rounding).
The threshold for damage is also affected by outside factors. Eg corrrosion can weaken the fastener.
A chamferless tool with greater engagement area might outperform in real world applications when looking at certain cases, such as low profile fasteners with high levels of corrosion
rockettauto
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High and low being relative of course. If it's a low pro fastener it's pretty much automatically in the low torque category.
Fork caps are a good example. 30ftlb on a 35mm nut is very low.
Moving up up a level we get into spanner nuts which make a good option when torque requirements are basically too high to get practical engagement on a hexagonal nut in the allotted profile.
rockettauto
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Red arrow shows where a chamfer can help spread stress.
Yellow arrow shows why the radius ( or fillet) is important on the outside for the same reason.
These are not locations where you want sharp angles to concentrate force.
Also part of why many don't use a sharp hex but rather rounded corners.
PretendMechanic
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I didn't read all that but I'm here to say I also hate chamfer on sockets and wrenches.
PretendMechanic
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Not as pissed as you'll be once you round off that bolt head...
I’ve been in this boat. To tell the truth, when you are working on low height nuts, seized or otherwise, you know it. It’s avoidable. In my case it was jam nuts on a landing gear door. This is a place where the FD+ open end shines. Even a box wrench had too much chamfer.
I would NOT buy special sockets for this application.
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