coined countersinks

I've designed coined countersink holes with coin relief on the backside. I found that "conservation of volume" is a sound approach. Volume displaced by the countersink has to go somewhere (steel is effectively incompressible at that scale). An equal volume is moved into the coin relief volume Coin relief geometry: cylinder of known height, OD, and ID concentric with hole and ID same as hole.

You could use the same approach, oversize your holes based on the volume of steel which will be displaced by your countersink cone.

Outside of making a test piece, volume is the only guesstimate I know of. However, it never fills the hole as much as it should. Metal doesn't compress, but it finds a place to go. Most of the time that place is up, the top of matl around the outer dia of the csink will bulge. We usually make the csink punch with a ledge to spank the top.

I have a listing of standard flanged 45deg lightening holes we use in the aerospace industry in for different thicknesses in aluminum. This calls out the blank hole size, would this be of use?

Thanks for the suggestions. Mate Precision Tooling sent an excel sheet that suggests a punch size for a given countersink and material. I can forward it to anyone interested, or you can request it from them.

diego

It would be usefull - I have to put an M5 c'snk into a 1mm sheet for a particular project.

Could you email the xls to snipped-for-privacy@SPAMuko2.co.uk - remove the SPAM

Thanks

TTFN

Jonathan

Hi Diego

I could use a copy of this, it's bound to come in handy in the new year.

John Layne

I'm having trouble decifering the email's - maybe it's the holiday punch from the company party. Please send an email to snipped-for-privacy@genmet.com and I'll forward the xls.

Another rule of thumb from Wilson Tool

Approximate pre-punch size = ((countersink size - thru hole size) x .75)

--subtract this amount from the original countersink dimension

Example: 82 degree x .507 x .266 thru hole:

.507-.266 = .241 .241 x .75 =.181 .507 - .181 = .326 approximate pre-punch.

Use the next size-up punch diameter available for the first try.

(thanks to Wilson Tool for this rule of thumb)