The usual method to retain the center piece is to make connecting tabs at the bottom face, thin enough to easily cut away then treat the edge to remove any trace of them, or remove the center piece by working it around until the tabs break then making a final cleanup pass around the hole.
Another way is to mount the piece to a plate or fixture larger than the piece and drill and tap a couple of holes into the waste to secure it to the plate. Mill around the waste to finished hole size. Yet another method which has proven to be highly resistant to coming loose is masking tape and super glue. Lay masking tape onto the bottom of the workpiece and top side of the fixture. Do not overlap the tape. Burnish it down for good adhesion. Apply super glue to the tape then press and wiggle the workpiece onto it. Allow the glue to fully harden. There's video on YouTube showing how well it holds, and how it can be pried apart and cleaned up. For an example of a huge job that was mostly waste, there's the Isogrid panels made for Skylab. Panels like that made today would be mostly abrasive water jet cut rather than NC milling out the huge numbers of triangles. If you ever want to exactly duplicate the grid dimensions used in Skylab, they're on the 42nd page of a poor quality PDF of Isogrid Design Handbook - NASA CR-124075 Rev. A 1973. I'd love to get a clean scan of an original copy of that. Heck, I bet NASA would love to get such a scan. On Tuesday, February 28, 2023 at 02:27:52 PM MST, Todd Zuercher <to...@pgrahamdunn.com> wrote: I need to mill about a 3.75" hole through a piece of aluminum about 1.75" thick. What is the best strategy to accomplish this on a cnc mill. Is it best to us a pocketing strategy and mill out the entire hole from the center out, or would it be better to use some kind of cutting strategy and mill some size slug out of the middle? I can see the first option being simpler, but the 2nd option saves a potentially useful piece of material, but with the added complication of how to hold and prevent the chunk of scrap from wreaking havoc when cut free. _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
