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Holes close to bends

Question asked by Bernie Daraz on Oct 13, 2016

Back in the mid-90's I worked for a high precision, high quality job shop, They didn't hesitate to take jobs but they wanted to make money on all of  them. We quoted this 16 gauge CRS with .312 return flanges on the top, all fully seam welded. They had tapped holes on the top that were too close to the bend and they brought in a sample of what their last vendor did. They actually punched clearance slots through on the center of the bend line.


We used a 1.5 times the material thickness to the edge of a hole as a guide for how close we could put a hole near a bend.


Of course we wanted another customer so I reground a standard .062 x .250 rectangle punch with a chisel shape, I programmed the part upside down and punched these chisels onto the bend centerline at the hole locations. I had thought the pulling on the outside of the bend was part of the problem but it was really the compressing of the metal on the inside of the bend.


Needless to say it worked, we were able to tap the parts in the flat, timesave and bend them without issue. There was no distortion to the holes.


I added a part file showing the .25 long chisel as a sample, soon we had them in .50 and 1.00 long in both form down and form up. We had three turrets so be bought additional ones as they were required. I don't think the angles are that important but the purchased tools were 90 degree. This also requires a flat bottom die for form down use.


This works really well on sharp and coined bends and also with the standard Amada tooling .008 radius. Aluminum would sometimes show the dimples from the chisels on the outside when the timesave direction matched the chisel direction after bending. I wouldn't suggest this it if you're air bending or with a punch radius of more than .008 though.


I'm sure from the part attached you can figure it out.


Hoping some of you can make use of this.