Maximum shop head thickness

[borislav]

Hi,

The milspec for solid rivets (MIL-R-47196A) gives minimum shop head diameter, as well as minimum and maximum shop head thickness (table III). Why is there a maximum thickness? I'm not an engineer, but I find it hard to imagine how additional material would lead to reduced strength, assuming the same head diameter.

Is it important to diligently smash my rivets until they are below the maximum thickness? If the rivet starts out on the long side, the minimum diameter is met way before that.

Thanks,
Boris

[Danny7]

just try to stick with proper lengths sticking out (99% of the time the plans are right) and squish them to average the right diameter and you won't have to worry about them meeting minimum diameter and maximum thickness at the same time

if you are getting the right diameter and you are over thick, your rivets are to long and you will end up folding to many of them over and the good ones won't be a bit stronger than a normal one, so what is the point?

[terrykohler]

Boris:
The unsupported length of the rivet shank can't be too long, or the column will buckle rather than upset into a shop head - cold forming first principles. Too short a shank, and you won't have enough material to form a proper head. Rule of thumb is to use 1.5 "diameters" for unsupported length. That is, if the rivet is 1/8 in diameter, the unsupported length should be 3/16 in. Vans makes it easy by calling out lengths to be used which come close to 1.5 diameters. This way, if the shop diameter is correct, the height will be correct, and vice versa. Without the length call-outs, we'd need to know the thickness of the sheets to be joined (in diameters) and then add the 1.5.
Terry, CFI
RV-9A N323TP

[az_gila]

Originally Posted by borislav

Hi,

The milspec for solid rivets (MIL-R-47196A) gives minimum shop head diameter, as well as minimum and maximum shop head thickness (table III). Why is there a maximum thickness? I'm not an engineer, but I find it hard to imagine how additional material would lead to reduced strength, assuming the same head diameter.

Is it important to diligently smash my rivets until they are below the maximum thickness? If the rivet starts out on the long side, the minimum diameter is met way before that.

Thanks,
Boris

...defined for clearance issues with adjacent assemblies rather than strength issues.

It is a "universal" specification to cover all conditions, and would give a mechanical designer a specific maximum height number to work with.

[plehrke]

Originally Posted by terrykohler

Boris:
The unsupported length of the rivet shank can't be too long, or the column will buckle rather than upset into a shop head - cold forming first principles.

It is a strength issue because too much cold forming (squeezing a "too long" rivet and thus making a "too big" tail) of the tail will make it brittle and may crack and eventually break off in fatigue.

[az_gila]

Originally Posted by plehrke

It is a strength issue because too much cold forming (squeezing a "too long" rivet and thus making a "too big" tail) of the tail will make it brittle and may crack and eventually break off in fatigue.

...since if you overdrive a too long rivet you will get very large diameter shop head.

The "over driving" would then be covered by the maximum shop head diameter - and guess what, there isn't a specification for that number...

Any failure in a too large diameter shop head would be created by cracking, which is covered in the specification.

The "too big" tail in a thickness direction would actually be less driving and therefore cold forming would not be a problem.

It would take a steady true hand with the bucking bar to drive a too long rivet, so using the correct length rivets is still the best idea...