On flat surfaces you can fit in the milling machine it’s quite easy to do. Use a rubberized abrasive stick and step off a grid pattern.

For curved surfaces it’d take more skill and layout.

I’ve done larger somewhat crude versions very quickly with 2” scotchbrite pads (like used in a die grinder/sander) in the drillpress. Layout guide lines with a magic marker first.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-