Stress risers in countersink holes?

[NWade]

Just a note on the "Knife Edge" terminology. This can mean different things to different people!

Commonly, I've seen this referred to when talking about running a countersink too deep; or trying to countersink a material that's too thin. See this picture for an exaggerated example of a "good" countersink and a "knife edged" countersink:
https://goo.gl/photos/sPmGuKMNNKW39R5k8

The problem with the "knife edged" hole in this example is that it might have opened up the diameter to be too big, *and* the thin material near the hole doesn't have enough structural strength to prevent the rivet from tearing through (or at least deforming the material) when its put under any kind of load or strain (especially over time).

Enjoy,

--Noel

[kevinh]

hmm - the depth should stay good even if doing it by hand but you might need to tape the little lockring on the countersink to make sure it stays locked. Typically I test on some scrap, find the depth then tighten the locknut hand tight and wrap it with a piece of tape then go at it...