What press force is needed ?

Go to a site such as

look up the shear strength of your material of choice noting the units psi..N/m^2 etc and converting if required.

The force you need will be the area you're cutting through multiplied by the shear strength, plus a bit for luck.

HTH

Mark Rand RTFM

You can reduce the amount of force by grinding an angle on the punch.

Area, or is it perimeter?

Joe Gwinn

Area I think. Which would be permimeter x material depth x shear

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Area of the sheared material, but not of the piece being punched out. That's the distinction I was making.

Joe Gwinn

Force = sheared area x shear strength of the material x punch geometry fudge factor

Yes, I guess I skipped that part of the explanation. My bad.

Mark Rand RTFM

The formulas are in _Machinery's Handbook_, including coefficients for steel and (I think) aluminum.

But basically, it is based on the total length of the cut (circumference of a circle, or 4 x the length of the side for a square.) Thickness comes into the equation as well, of course.

What is the symbol after "1 cm" in your quoted text above. It appears to be an extended ASCII character which displays differently on different systems, and with different character sets loaded. On my system, it shows as "\262", which is a value which won't display on my system. Is it perhaps a superscript '2' to indicate a square cm? Is so, the cut length will be 4 cm.

You do have a _Machinery's Handbook_ don't you? if not, you should.

Good Luck, DoN.

Y^u multiply the length of the shear line by the thickness of the metal being punched. That will give you an area .. length x height.

You then look up the shear modulus of the metal you are punching which is usually given in units of force per area.

multiply you area by the shear modulus and that number is the ideal force you will need.

other factors are how sharp is your punch. Temper of the metal. How well your punch clearances are. How your punch is tapered so it does not hit the whole shear line at once.

That will give you a starting point. You probably should allow about 20 percent more force than the formulas come up with until you run some jobs and see how the press handles them. If you are using an older back geared press in good shape the tonnage is almost always underrated. An older 90 ton Bliss looks beefier than a newer 150 ton.

Have fun and watch your fingers.

John