Hello,

I added a mill recently to our facility to make prototype injection mold dies and I am attempting a task to modify an existing mold, of hardened tool steel (A2) to 60HRC. In order to make necessary modification I need to make a pocket approx 1.75" x 2.0" and 0.5" deep, this pocket will accept inserts of with varying features and tight side tolerances. In order to do a test before machining the valuable mold die I picked up a piece of hardened steel to test the same pocket. As expected, using standard end mills resulted in cutter deflection as I went deeper into the pocket. I was able to hold very tight tolerances at the top surface of the pocket but as I went deeper there is a resulting taper from cutter deflection of about 0.002" on all of the side walls. I took effort to relieve the corners with a smaller diameter end mill in order to prevent cutter deflection, but it looks like even the smaller end mill deflected as well.

My question is, are expensive relieved end mills absolutely necessary to achieve straight side walls, or are there other methods to achieve a straight wall, using standard end mills?

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