Countersink Angle Questions
 

Hi All,
Most of my tooling has been collected from auction sales and odd lot purchases.
While searching thru my motley collection of countersinks, I started wondering
about all of the different angles.

60 degree included angle matches lathe centers -- but I do not ever recall
using anything other than a combination center drill/countersink for this
application yet I have some single flute and multi-flute 60 degree
countersinks. Any other applications?

82 degrees included angle seems to match most flat head machine screws --
though I do not understand why the industry would have standardized on 82
degrees rather than some nice round number.

90 degrees included angle seems to match a few machine screws and is the
intuitive choice for deburring and chamfering. Would have seemed like a
logical choice for all machine screws.

100 degrees included angle -- I do not know why I have any of these

120 degrees included angle -- unclear on what these are used for as well.

Can anyone offer any insight? Seems like there must be some logic, but my
meeger collection of reference books is silent on the topic.

Thanks,
Mill

"MP Toolman" wrote in message
...

120 degrees included angle -- unclear on what these are used for as well.
Thanks,
Mill

Don't know for sure but it should match the angle of a 60 deg. thread. Use
it to c'sink holes before tapping.
Randy

MP Toolman wrote:

Hi All,
Most of my tooling has been collected from auction sales and odd lot purchases.
While searching thru my motley collection of countersinks, I started wondering
about all of the different angles.

60 degree included angle matches lathe centers -- but I do not ever recall
using anything other than a combination center drill/countersink for this
application yet I have some single flute and multi-flute 60 degree
countersinks. Any other applications?

82 degrees included angle seems to match most flat head machine screws --
though I do not understand why the industry would have standardized on 82
degrees rather than some nice round number.

90 degrees included angle seems to match a few machine screws and is the
intuitive choice for deburring and chamfering. Would have seemed like a
logical choice for all machine screws.

100 degrees included angle -- I do not know why I have any of these

120 degrees included angle -- unclear on what these are used for as well.

Can anyone offer any insight? Seems like there must be some logic, but my
meeger collection of reference books is silent on the topic.

Thanks,
Mill

100 degrees is pretty much the standard (OK, one of the MANY standards,
but a common one) for aircraft screws and countersunk rivet heads.

IIRC I have seen references to aircraft rivets and screws that use 120
degrees as well, mainly for thinner sheet stock.

Cheers
Trevor Jones

MP Toolman wrote:
Hi All,
Most of my tooling has been collected from auction sales and odd lot purchases.
While searching thru my motley collection of countersinks, I started wondering
about all of the different angles.

60 degree included angle matches lathe centers -- but I do not ever recall
using anything other than a combination center drill/countersink for this
application yet I have some single flute and multi-flute 60 degree
countersinks. Any other applications?

82 degrees included angle seems to match most flat head machine screws --
though I do not understand why the industry would have standardized on 82
degrees rather than some nice round number.

90 degrees included angle seems to match a few machine screws and is the
intuitive choice for deburring and chamfering. Would have seemed like a
logical choice for all machine screws.

100 degrees included angle -- I do not know why I have any of these

120 degrees included angle -- unclear on what these are used for as well.

Can anyone offer any insight? Seems like there must be some logic, but my
meeger collection of reference books is silent on the topic.

Thanks,
Mill
the 100 and 120 are mainly seen on rivet heads. Metric flat head screws
use 90 instead of the english 82 (not sure where that one started either)

On Sun, 28 Nov 2004 10:36:58 -0400, James P Crombie
wrote:

MP Toolman wrote:
Hi All,
Most of my tooling has been collected from auction sales and odd lot purchases.
While searching thru my motley collection of countersinks, I started wondering
about all of the different angles.

60 degree included angle matches lathe centers -- but I do not ever recall
using anything other than a combination center drill/countersink for this
application yet I have some single flute and multi-flute 60 degree
countersinks. Any other applications?

82 degrees included angle seems to match most flat head machine screws --
though I do not understand why the industry would have standardized on 82
degrees rather than some nice round number.

90 degrees included angle seems to match a few machine screws and is the
intuitive choice for deburring and chamfering. Would have seemed like a
logical choice for all machine screws.

100 degrees included angle -- I do not know why I have any of these

120 degrees included angle -- unclear on what these are used for as well.

Can anyone offer any insight? Seems like there must be some logic, but my
meeger collection of reference books is silent on the topic.

Thanks,
Mill
the 100 and 120 are mainly seen on rivet heads. Metric flat head screws
use 90 instead of the english 82 (not sure where that one started either)
The 120 degree is also used for countersinking the holes for
Heli-Coils.
ERS

Or could be used for chamfering any 60 degree threadform hole.

Eric R Snow wrote:


The 120 degree is also used for countersinking the holes for
Heli-Coils.
ERS

On Sun, 28 Nov 2004 17:37:35 GMT, machineman
wrote:

Or could be used for chamfering any 60 degree threadform hole.

Eric R Snow wrote:


The 120 degree is also used for countersinking the holes for
Heli-Coils.
ERS
That's true, but usually the callout for chamfering a threaded hole is
45 degrees. In fact, I've never seen a 120 degree callout except for
the STI thread. Heli-coil says this is for ease of inserting the
heli-coil STI. But, since I've not seen every drawing I can't say it
isn't done. Or even that it's not common.
ERS

MP Toolman wrote:

100 degrees included angle -- I do not know why I have any of these

Very common in flat head rivets intended for relatively thin sheet
metal. e.g. Aluminum skins on aircraft.

The "flatter" countersink and rivet head gives more contact area - less
likely for the rivet head to pull through the sheat metal.

Ted

True, I used to do a lot of helicoil repairs, (aircraft engine repairs)
but we usually used a 45 degree chamfer. With the proper installer(the
type that constrain the helicoil) the chamfer is not a problem. I can
see it helping if your using the standard screw type installer. We also
used to do a lot of twinsert repairs, a helicoil in a helicoil, for when
the previous repair had failed or the magnesium had corroded away.

Eric R Snow wrote:
On Sun, 28 Nov 2004 17:37:35 GMT, machineman
wrote:


Or could be used for chamfering any 60 degree threadform hole.

Eric R Snow wrote:



The 120 degree is also used for countersinking the holes for
Heli-Coils.
ERS

That's true, but usually the callout for chamfering a threaded hole is
45 degrees. In fact, I've never seen a 120 degree callout except for
the STI thread. Heli-coil says this is for ease of inserting the
heli-coil STI. But, since I've not seen every drawing I can't say it
isn't done. Or even that it's not common.
ERS