Flat washers for SHCS's

[shermanb]

I have recently ran into an issue finding proper through-hardened flat washers for use with socket head cap screws.

It seems that every flat washer specification I find gives a possible interference between the ID of the washer and the underhead fillet of the SHCS.

The socket head cap screws have material hardness specified by ASTM A574. Their dimensions are defined by ASME B18.3.

Is there a good solution out there??

 

[shermanb]

....I should mention that even the dimensions given by the ASTM F436 specification interfere with the underhead fillet of the SHCS

 

[TVP]

ASTM F436 washers should be compatible with SHCS according to ASME B18.3. For example, a 1" SHCS has a maximum diameter at the fillet of 1.10" and the associated 1" washer has a nominal ID of 1.125 + 0.031" tolerance.

 

[shermanb]

This is true. But, what about nominal sizes of 3/8" -7/8"? Those sizes show possible interference with a F436 washer.

 

[TVP]

It is difficult for me to understand how ASME and ASTM allow this sort of thing to happen. There is probably some lame excuse, but I do not know anything about it.

What I can tell you is that using ISO standards eliminates this problem. Specifying a socket head cap screw (M6) according to ISO 4762 shows that the maximum diameter associated with the fillet (called d_a) is 6.8 mm. The inner diameter of the corresponding washer (ISO 887) is 6.4 mm with a tolerance of - 0/+ 0.18 according to ISO 4759-3.

 

[MintJulep]

While theoretically there can be interference, hopefully there usually won't be.

Not very satisfying is it?

Apparently the washer committee and the bolt and screw committee don't talk to each other.

 

[KENAT]

Do the washers call for a slight edge break on the hole? Or is it assumed they'll deform a little if need be?

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