I NEARLY GIVE UP! ■

1 - As I understand it this is a punch and die issue. I remember looking at this years ago. There is nothing in Machinery's Handbook, but there are books which deal with this subject in commercial production engineering (it's a bit left field for some of our bulk solids friends. Try Eng-Tips Forum on the net).

If you want a precise 25 mm square you have to make the die about 1% larger each side - like 25.5 mm square. But it depends on the material you are punching. When in doubt tool makers make a model and check it out on a press.

2 - Free area is a loose term. You are looking at punching a screen cloth. You are looking at the hole pattern. If you hold it up to the light free area is where you see daylight - anything that is not obscured by solid. However, if you are marketing the whole screen cloth panel you must deduct the solid area around the edges. The screen manufacturer will also have to deduct the edge strips and support bars running across the middle. Talk to a screen manufacturer. They will be happy to set you right. ■

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Keep Smiling, George Baker - Moderator ■