Countersinks

[lynnl]

Are most countersinks, ie. normally encountered, eg. flathead screws in consumer items, 82 degrees? I bought a nice countersink some time ago thinking I needed a 60 deg CS, and it never seems to match what I need. I'm now trying to fit a big Porter Cable plunge router to one of those phenolic drop-in tops for a router table and those screws seem to be about 82 degs.

[Dr. Rob]

Nope. Lots of 'em are 90*. It varies a little among SAE, Metric, wood and so on. I have a chart somewhere, don't know exactly where though. If nobody else pulls a link outta their sleeve, I'll have to go find it for you.

[lynnl]

Thanks Dr Rob, but don't bother doing any research tho. T'was more just a matter of casual curiosity. I just bought an 82 deg one anyway.

[Thrud]

Lynn

Almost all screws are 82*. For some reason door butt hinges have 90* countersinks and the screws never fit properly. All the metric countersunk hex screws I use are 82*.

I use Severance 6 flute non-chattering countersinks, but the uniflute work well (and in wood), as do the Weldon type (a hole through the cutter)

60* is normally a center lap. 100*, 90* countersinks are also sold, these are more for beveling holes than anything.

[uute]

Ahh, the things you learn here. On a #10 screw, it is a real bear trying to measure the head angle close enough to tell 82 from 90*. (only 4* diff on one side.) ; )

[Randy]

By my experience (and a quick look at Machinery's Handbook) metric flat head machine screws and cap screws are 90*. Of course the vast majority of American screws are 82*. 100* heads are often used with sheet metal where you need a low profile. You can get 110* and 120* c-sinks also. What I wonder is, who came up with 82* rather than a nice "round" 90*, and why. There's probably a sensible reason, or rather a reason that was sensible 100 years ago

Oh, yeah, I can usually judge a screw head's angle pretty readily by holding it at a 45* angle and sighting one flank against the top edge of, say, a door, line it up and see how the other flank lines up with the side of the door. Works for me, even with #4 screws.

[This message has been edited by Randy (edited 03-15-2003).]

[lynnl]

Yeah, that was the burning question I forgot to ask, Why 82 degrees? Tho that may be one we'll never know.

[Kevin45]

Our flat head machine screws where I work are 100deg c'sink, all flat head allen screws are 82deg c'sink. Very rarely do we ever use a 90 or a 60.

Kevin

[Thrud]

Lynn
I think it was a pissing contest and someone lost...