CNC Challenges

I am making a new Mechanical Marvel (stay tuned for another Amazing Adventure in the Land of Prof. Henry), and used the CNC to make a part out of a 3/32” thick brass sheet. I was happy with the result and thought it was going to be a splendid part of the mechanism … until I weighed it.

The part weighed 3.125 ounces, and since it will attach to another much heavier piece that needs to be counter-balanced, I needed to shave some weight. So I set up a new file that would remove weight by cutting out the interior of the part. All I had to do was put it back on the CNC and cut out the section to be removed.

But how? CNCs are easy to set up for making your cuts, but it’s challenging to realign things once you’ve removed the piece from the machine when you didn’t plan ahead. Now I had an awkwardly shaped, roughly 4.5" x 4" piece that I needed to get square on the table, and somehow identify the center where the original cut was zeroed.

[Cue quiz game music while The Professor ponders.]

My solution was to go back to the CAD program and create a new file using the existing part’s vectors and center them on a larger piece of MDF. By cutting a shallow pocket the shape of the part, I could place the piece of brass in the pocket and know that everything was square and centered for making the new cut.

Once the pocket was cut on the CNC, I placed the brass part in the pocket and held it in place with double-sided tape. The result was a new cutout on the existing part with no problems and no missteps, and I was able to lighten the part by a third. Now I need to get busy on the rest of the parts.