coined countersinks

We frequently coin countersinks in sheet metal. The process is done on a turret by punching a thru hole and then restriking the hole with a countersink punch and die set. The material is offset into the thru hole and that has to be figured into the thru hole punch diameter because the material moves and closes up the hole size.

Does anyone have a rule of thumb for figuring the initial punch size? Trial and adjustment is our current method. Various material types and thicknesses have an effect.

Any help is appreciated. Diego

Reply to
Diego
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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.

Reply to
That70sTick

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.

Reply to
Diemaker

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?

Reply to
Phil Evans

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

Reply to
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

Reply to
jjs

Hi Diego

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

John Layne

formatting link

Reply to
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.

Reply to
Diego

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)

Reply to
Diego

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