To expound on William’s explanation when he says you can calculate how much material to remove under a screw head.
The calculation is very simple. Divide one (as in one inch) by the pitch of the thread, that’s it. Knowing the pitch of a thread will tell you how far any given fastener will advance when it’s rotated exactly one full revolution.
For example, a pitch of 20 threads per inch (tpi) is calculated as follows: 1 ÷ 20 = .05. In other words, one full revolution of a 20 tpi screw will advance fifty-thousandths of an inch (.05).
A screw thread with a pitch of 48 tpi will advance .0208 per full revolution. (1 ÷ 48 = .0208)
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To expound even further on the subject of threads, for those who are interested; a fine thread is generally stronger then a coarse thread (mechanically). The trouble with a fine thread in some cases is how many turns the hardware requires to drive the fastener home. This is resolved by machining multi-lead threads. For example, a 20 tpi double lead thread will advance twice the distance as a single lead thread or, one hundred thousandths per revolution. (.1). That’s achieved by chasing two separate threads with a pitch of 10 tpi that begin (and end) exactly 180 degrees from one another on the workpiece. A triple lead thread - same thing only now the workpiece has three individual threads that begin, and end, exactly 120 degrees from one another. From an engineering and manufacturing perspective, the number of leads is basically unlimited, especially since the advent of CNC that greatly benefits set-up time in comparison to setting up an engine or tool room lathe to achieve the same thing. On a CNC lathe, or mill using thread mills, it’s literally a few additional lines of code and you’re all set.
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