Making a DB9 connector punch

chucklippmeier

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Jan 11, 2016
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I have struggled mightily to figure out how to make a punch to make holes in 1/16" aluminum chassis. There have been quite a few trials and errors along the way and I'm still not happy with what I'm doing. The punch is the problem and the die doesn't seem to be a problem. The punch is trapezoidal shaped with rounded off corners and the problem is to figure out how to make the cut to round off the corners.
I'm working with a Series 1 J-head Bridgeport mill and a 12" Phase II rotary table.
To start I drilled and counter bored three (one side) holes in a 1" aluminum plate. The two outside holes are separated by the distance between the DB9 mounting screws and the same diameter. The third hole is 1/4" and centered between the other two holes. The work piece is a squared up block of 01 Steel with three holes to match the three holes in the aluminum plate. The two outside holes are tapped for an 8X32 screw and the centered hole is tapped for 1/4X28. The work piece is mounted to the aluminum plate. The whole assembly is clamped down to the mill table and four 1/16" holes are drilled at the radius centers of the 4 corner OD curves. I then put a pin in one of the corner holes and loosely mount the assembly to the rotary table. I set the rotary table so the mill's X and Y axis are lined up and cut the trapezoid with sharp corners. I mount a drill chuck in the mill's spindle and use it to grab the pin in the work piece so I know the mill spindle is centered on the first radius I want to cut. I remove the drill chuck and mount an end mill in a spindle collet. Using the mill's Y-axis adjustment I move the work piece toward the outside edge of the trapezoid a distance equal to the radius I want to cut plus the radius of the end mill. I lower the end mill to the depth of my first cut, turn on the mill and rotate the rotary table so the work piece gets turned into the cut. The sides of the trapezoid are 10 degrees so depending on which corner I either rotate the rotary table 80 degrees or 110 degrees. Then I repeat the process for the other three corners.
At this point I've made a mess. The rounded corners are not uniform. Some dig into the trapezoid and some don't make it to the edge of the trapezoid. I'm thinking that I'm suffering from back lash. Since each corner will start and end with different loads on the various axis how do I take up the back lash before the cut so the various axis are tight all the way through the cut and without loosing my center registration and my x and y axis parallels? Or, am I just doing it wrong altogether?
 
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