Both thread milling and tapping are widely accepted methods of machining threads through a hole in a panel or machine part. Most shops prefer tapping, though thread milling a hole may yield valuable results for your project.
Advantages of Thread Milling
A thread milled hole is processed at a high RPM, allowing the machinist to better control the thread size and fit, especially because a thread mill tool works in a previous milled hole.
In using the thread milling technique, machinists are able to create a wide variety of hole sizes and reduce the logistics costs that come with additional tool changes.
Thread milling also allows for custom threads, interior and exterior-facing threads, and even right-hand/left-hand threads. Pipe threads and other large threaded holes are possible with thread milling.
Advantages of Tapping
Tapping machine or panel holes allows for extremely fast processing speeds. High-speed tapping machines can process holes in a small fraction of the time required by thread milling. Tapping is also able to penetrate much deeper holes within rigid materials like steel or tungsten carbide.
While tapping doesn't allow for much flexibility as far as different sized holes (that requires multiple tool changes), it's able to quickly and easily plunge through materials completely. It's not the ideal process for holes that end within the material itself, but when you need quick processing through very hard material, tapping is the way to go.
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