Over the past 4-5 months I've been making a wide variety of different parts for a 6-axis robotic arm I'm working on. With at least 20 unique milled parts in a variety of shapes and sizes, this project has forced me to learn how to make my workflow from 3D model to first part off the machine a lot more efficient, as most of the parts I make are quantities of one or two. So I thought I would share some of the things I've learned along the way I wished I knew about sooner.

A couple weeks ago I spent some time making a small tooling plate to help make some parts used for the wrist joint of the robot. I wish I had made one of these sooner as it is looking like it will be useful for all different kinds of parts. It was made from a roughly 6"x6"x3/4" piece of 6061. I decided to make it as a vise fixture because it would only be needed for relatively light machining, and this would allow me to use either the vise or tooling plate without having to pull the vise or re-zero things. I started by cutting two pockets on the back side of the plate, so that I could drop it into the vise and have it locate to the same spot every time without any other tools.

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The plate was then flipped and placed into the vise as it would be used and the top machining was done. The top was milled flat to a depth of .200", leaving a lip on the top and left sides so that stock can be brought square to that corner. If you preferred, any other corner could be used as well. The top and left corners were milled to be exactly 5.5" and .2" from the bottom left corner. I then drilled and tapped a grid pattern of 10-32 holes over the plate (the T/C tapping head earned its keep on this one!). The rows of holes are spaced .5" apart in X, and staggered in groups of two alternating rows in Y. One row was .5" apart starting .5" from the top lip, and the other was .5" apart starting at .75". The spacing was chosen to work with the Mitee-Bite fixture clamps I've accumulated a collection of from previous projects. The clamps work with an offset of .250" from the stock edge, so with the hole pattern I can place clamps on any piece of stock that is a multiple of .5" in X, and a multiple of .5" or .25" in Y.

With this fixture plate I was able to quickly set up and machine some pieces which required machining virtually all of the interior space of the part, as well as profiling all the way around. Here is a (mostly) finished part.

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The way this worked was to do it in two setups. One with slightly oversize stock gripped around the edge would perform all of the interior machining, including a pocket and placing holes. Because the fixture plate uses a .5" grid, it is easy to add holes to a part or use existing holes to locate it. These would be used to both locate and hold the part in the second setup, which machined a profile all the way around the part. I set this up in my CAM program by making two copies of the part, located at the two positions on the fixture plate, so that I could have both setups on the fixture at the same time. This reduced tool changes per part and would also allow me to make copies quickly (though I only needed two in this case) as each machine run would produce one finished part. Here is a preview of what the toolpaths looked like:

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And here is what it looked like after running them:

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These are not particularly complex parts by any means and there are many other ways one could approach this, each with their own advantages and disadvantages. I appreciate seeing walk-throughs of how other people have solved problems as it helps to build my mental library of ways to approach a new part. This approach saved me the trouble of having to locate the part origin multiple times (once you have located the fixture, everything else comes from that), and I could do all different kinds of profiles without having to use soft jaws.