1. Home
  2. ⏣ General Metalworking
  3. Countersink Angle Questions

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

Reply to
MP Toolman
Loading thread data ...

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

Reply to
Randy Replogle

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

Reply to
Trevor Jones

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)

Reply to
James P Crombie

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

Reply to
Eric R Snow

Reply to
machineman

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
Reply to
Eric R Snow

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

Reply to
Ted Edwards

Reply to
machineman

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.