Washer undercut

[Harry WilkesParticipant @harrywilkes58467]

[Harry WilkesParticipant @harrywilkes58467]

Morning All

I have justed watched a YouTube video the guy was making some dome headed hex screws and he made what he referred to as a 'washer undercut' under the head the purpose was to stop the head from damaging the paint work when tightened. I couldn't see very clearly what he had done and as I am making some hex head fasteners wondered if anyone could explain the technic

Thanks

H

[Brian GParticipant @briang]

I assume he means turning the underside of the head down to the across flats dimension for a few thou so that it doesn't mark the paintwork as it is tightened.  As far as the paint is concerned it is then a cheese-head screw.  I keep putting off doing this to the screws on a 16mm loco but it is much tidier than washers.

Brian

Edited By Brian G on 31/10/2017 09:46:17

[EmgeeParticipant @emgee]

I understand undercut to mean traversing a cutting tool with a clearance angle deeper into the work so avoiding the fillet left by the tool interfering with the screw seating when tightened.
The depth of the undercut needs to be at least as much as the tool tip radius.

Agree with Brian the method to help avoid damaging paintwork.

Emgee

 

typo

Edited By Emgee on 31/10/2017 09:54:28

[Paul LousickParticipant @paullousick59116]

Is this the bolt head feature which you are refering to ?

It is used on high tensile bolts.

Paul.

[Philip RoweParticipant @philiprowe13116]

I've always known this feature to be a 'washer face. Is this a term that is common/uncommon as I have used it on occasions and other people have looked at me as if I'm from another planet?

Phil

[SandgrounderParticipant @sandgrounder]

Posted by Philip Rowe on 31/10/2017 12:04:53:

I've always known this feature to be a 'washer face. Is this a term that is common/uncommon as I have used it on occasions and other people have looked at me as if I'm from another planet?

Phil

'Washer face' is the term I've always used and it's called that in the fasteners section of my 'British Standard Handbook No 18'.

John

[VicParticipant @vic]

This is quite interesting and does make sense but I can’t say I’ve ever seen a bolt like that before.

[Mick B1Participant @mickb1]

I don't know why you wouldn't use the same 30 deg. chamfer down to AF diameter that's on both sides of a standard nut. The paint would be affected in almost the same way – if anything with less damage, due to the absence of a right-angled edge.

[SandgrounderParticipant @sandgrounder]

Posted by Mick B1 on 31/10/2017 13:46:18:

I don't know why you wouldn't use the same 30 deg. chamfer down to AF diameter that's on both sides of a standard nut. The paint would be affected in almost the same way – if anything with less damage, due to the absence of a right-angled edge.

They do make 'washer faced' nuts as well. chamfer one side and washer face the other.

[JasonBModerator @jasonb]

I have seen it done on quite a few American models, seems they like their washer face nuts over there. Nuts for one such engine by Dave Otto

[KWILParticipant @kwil]

Makes it look like you have used a washer when you have not.

[Mick B1Participant @mickb1]

Purely a cosmetic feature then, with no engineering significance?

[MWParticipant @mw27036]

There are also ones where the washer face stands proud of the nut. Quite common in mill clamping kits actually.

Michael W

[Mick B1Participant @mickb1]

Posted by Michael-w on 31/10/2017 18:26:35:

There are also ones where the washer face stands proud of the nut. Quite common in mill clamping kits actually.

Michael W

Do you mean flanged nuts, where there's a larger diameter disc, with a shallow cone and the hexagon cut on top?

That makes sense where the nut is employed over a slot rather than a hole, as in clamps, as a plain or 'washer' nut could be bruised and distorted by being tightened into the slot. I've also made some big ones of these (1" BSW and up) for use on steam locos. Mostly these are castellated.

[Harry WilkesParticipant @harrywilkes58467]

Thanks for all the comments I did have in mind it would be as Paul's drawing but like Vic I have never seen one

[MWParticipant @mw27036]

Posted by Mick B1 on 31/10/2017 19:02:56:

Posted by Michael-w on 31/10/2017 18:26:35:

There are also ones where the washer face stands proud of the nut. Quite common in mill clamping kits actually.

Michael W

Do you mean flanged nuts, where there's a larger diameter disc, with a shallow cone and the hexagon cut on top?

Yep, Bingo, I wasn't really sure what to call it!

[Howard LewisParticipant @howardlewis46836]

Washer faced hardware has been available, and used for about 25 years, certainly on Perkins engines, (and probably many other companies)since they started making engines to metric standards, (rather than the Imperial earlier ones).

To prevent fasteners from slackening, the washer face can be serrated, sometimes at an angle to give "ratchet" effect, of easy tightening, but more difficult slackening.

Howard

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