11/ the shape of the cutter. American Unified Thread standard has 60° profile (IIRC), and that is easily derived though simple geometric
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Replying to @MorlockP
12/ construction with a straightedge and a compass. I've got a vague memory that the first high precision thread was hand made near perfect
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Replying to @MorlockP
13/ along a 1" or 2" length and then this was used as a lead screw in a lathe, thus allowing it to self replicate along length of workpiece
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Replying to @MorlockP
14/ but I can imagine the existence of other techniques. For example, the surveyor's transit is simple, but amazingly cool.
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Replying to @MorlockP
15/ Picture a tripod with a flat platen on top, engraved with degree markings. Then a telescope pivots atop that. Scope has indicator arrow
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Replying to @MorlockP
16/ Naively, I aim scope at church steeple #1, note degrees, then aim at steeple #2, note degrees, subtract, find angle.
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Replying to @MorlockP
17/ Problem is that precision is gated by the crispness of the incised angle marks on the platen. Not even talking accuracy in layout!
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Replying to @MorlockP
18/ Just noting that on a 1' dia circle, the width of the chisel incised layout ticks is very noticeable. 1/2 ° or more!
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Replying to @MorlockP
19/ I ran into exactly this when tramming in Bridgeport's head: head has angle markings. Setting it at 0° is just the start of the process
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Replying to @MorlockP
20/ So how does a surveyor's transit do its magic? The platen can rotate and there is a second indicator. Hand wavingly, you lock scope
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21/ to platen, rotate both, lock platen to base, unlock scope, pivot scope back to target, repeat. You're basically measuring same angle >
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Replying to @MorlockP
22/ 10 times, and thus your 21° angle is measured as 210° degrees. You divide by 10...and your ERROR is divided by 10 as well.
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Replying to @MorlockP
23/ So that's the magic: a process that lets the signal stay at full strength by adding it in 10 times, but gaussian error self cancels.
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