Here I show my method using a touch probe and custom routines to identify reference holes to align top and bottom machining processes on a CNC router. No jigs or fixtures necessary!

Affiliate Links
Standard 1/4" plunge router bit: https://amzn.to/3LB8zi3
Long 1/4" plunge router bit: https://amzn.to/3y8p4yZ
CNC Dust Foot: https://amzn.to/3WxwaWZ

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