Why are washers such a poor fit?

[VicParticipant @vic]

I’m sure someone knows the answer. I’ve long wondered. As an example I bought some M6 screws the other day and the major diameter is 5.84. A quick measure of some M6 washers bought at the same reveals an ID of 6.5. I’m guessing it must be something to do with preventing vibration from loosening the fastener or something. Poor show really though as it looks crap!?

When I made some thick washers for my milling vice bolts though I made them the proper size and the nuts have never come loose.

[VicParticipant @vic]

[speelwerkParticipant @speelwerk]

Well they are dual use and a perfect fit for a 1/4 inch. Niko.

[VicParticipant @vic]

Posted by speelwerk on 24/09/2019 18:57:59:

Well they are dual use and a perfect fit for a 1/4 inch. Niko.

Hhm, still a bit big even for a quarter inch! I like your thinking though.

[Martin ConnellyParticipant @martinconnelly55370]

It is to allow the head to sit properly on the washer when there is a radius between the shank and the head. Eg a 2.5mm radius on a 6mm shank will require a 6.5mm clearance hole in the washer. A bolt/screw without a radius is weaker due to the stress raising effect of a sharp corner.

Martin C

Edited By Martin Connelly on 24/09/2019 19:07:54

[HOWARDTParticipant @howardt]

+1 for Martin.

if you intend to use the washer as a seating for a nut then by all means make the hole smaller and possible make the washer thicker. As an alternative locate the washer in a shallow counterbore to retain its position.

[Mike PooleParticipant @mikepoole82104]

A standard flat washer for 6mm should be 6.4mm I am sure there are other standards, I always think a fully machined washer with a chamfer looks nice but washers are used from the crudest of fixings to fine engineering so it’s probably worth finding or making them to suit the job.

Mike

[JasonBModerator @jasonb]

Metric clearance sizes are quite generous so it follows that washers are too. Normal clearance hole for M6 is 6.6mm with close and loose being 0.2mm either way. Just look at the pilot size on counerbores to see.

[Mick B1Participant @mickb1]

Posted by HOWARDT on 24/09/2019 19:20:57:

+1 for Martin.

if you intend to use the washer as a seating for a nut then by all means make the hole smaller and possible make the washer thicker. As an alternative locate the washer in a shallow counterbore to retain its position.

+another.

+also Mike Poole's comment – if you want a neater fit, it's not demanding to make your own for most ME-type quantities.

[Martin ConnellyParticipant @martinconnelly55370]

Should have said .25mm radius, not 2.5mm. I am surprised no-one picked this up!

Martin C

[Mike PooleParticipant @mikepoole82104]

Soft washers tend to spread and can go tight on the bolt, also happens with solid copper head gaskets, although steel washers tend to be more resistant they do spread with repeated use in extreme situations.

Mike

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