Custom Finger Brake Bending Die

Project Purpose

I needed a quick and relatively cheap way of bending 1/2” x 2” 6061-T6 aluminum bar stock to manufacture a custom strut tower brace for a BMW Z3. Outsourcing the bending to another shop would eat away all the profit I could make from manufacturing the brace so that wasn’t an option. The resources I had available to me was a SWAG Off Road 20 ton finger brake kit and a hydraulic press capable of providing enough force to take the 1/2” x 2” bar stock beyond its tensile yield strength. I also had all of the bending dies that the brake press came with but whose bend radii where all much too small to properly bend the 1/2” material with out causing serious deformation.

It was time to put my design skills to the work. A quick rule of thumb to choose an appropriately sized radii for bending says that at minimum the bend die radius needs to be equal to the thickness of the material. With that in mind, I went ahead and designed an upper and lower die out of 1/2” A36 steel that I could have SendCutSend manufacture for me. I probably should have chosen Steel with a higher yield strength given that 6061-T6 has a yield strength of about 40,000 psi and that of A36 is only about 36,000 psi, but it was the cheapest option and given the geometry of the upper and lower portions of my dies I assumed the pressure on the dies would be distributed fairly evenly amongst the components and not yield.

The Lower die was designed to have a 2” bend radius on the curved areas where the aluminum bar stock rolls over during the bending process. The trough of the die was designed with plenty of relief so the bar stock could be bent further than designed Just in case.