Talk:Thousandth of an inch

message: 0.0254 mm, or 25.4 μm (1 millimetre is equal to about 39.37 thou)  INCORRECT
0.254 mm, or 25.4 μm (1 millimetre is equal to about 39.37 thou)   correct
—Preceding unsigned comment added by 85.132.201.32 (talk • contribs) 01:12, September 12, 2006
: Actually 0.0254 mm does equal 25.4 μm —MJBurrage • TALK • 19:07, 8 June 2007 (UTC)
thread_title: Conversion

message: The taxation info should not be on this page. Superm401 - Talk 21:08, 23 March 2008 (UTC)
thread_title: Taxation

message: http://www.gsparkplug.com/shop/spark-plug-gap-settings was recently added to explain spark gap gaps, then deleted because it was a commercial site, the restored because it was claimed as useful. I'm not worried that it is a commercial site because it explains spark plug gaps well enough and doesn't push its products. It would probably be a good reference for the spark plug article. However, it doesn't explain anything about 'thou', the closest it gets is an example usage: 'The rule of thumb for the spark plug gap on older engines is coil ignition 0.025 thou and magneto ignition 0.018 - 0.020 thou.' Since this is not an article about spark plugs, I would like to remove this reference without continuing an edit war. Thoughts?  Stepho  talk  02:05, 14 June 2011 (UTC)
replies: text: I would agree with its removal - especially as that means there are now two reasons for it to go. --Biker Biker (talk) 08:18, 14 June 2011 (UTC)
replies: text: Yeah, not the best ref for this article, although it would be good in spark plug, if required. Wizard191 (talk) 15:17, 14 June 2011 (UTC)
replies: text: It has been removed from that article several times after being spammed by the site owner. --Biker Biker (talk) 16:39, 14 June 2011 (UTC)
thread_title:  spark plug gap 

message: I would like to clean up this section; I'll probably combine it with 'Unit Conversions'.
In particular, the entry '1 μm is approximately half a tenth, or 50 millionths.' is roughly 20% inaccurate, and I'll remove it.
Any objections?Benthatsme (talk) 01:48, 24 September 2014 (UTC)
replies: text: The reason for the section's existence (and separation from the precise unit conversions) is explained in its opening paragraph, and in my opinion, people who aspire to be good CNC operators (as opposed to pushing buttons blindly and spinning the roulette wheel to see whether scrap results) can learn valuable "feel" from it. It's about gut-level, intuitive, horse-sense comparisons—quick mental arithmetic while under pressure to be thinking about other things at the same time. To "feel" from moment to moment whether the numbers in front of you are wrong or right. Imagine the digital mic says your last wear offset change yielded a .003 mm difference in the part size. Quick!—tell me *now* (not 8 seconds from now)—how does that compare to .002"? Without thinking hard—without a calculator—without "doing a math problem". Can you do it? Did you know *instantly* it was way smaller, something like 1/15th to 1/20th the size—as opposed to 1/4, 1/2, or 1.5× the size? If so, you did it with arithmetic horse sense—not with a multiplication or division of a 3- or 4-digit number by a 3- or 4-digit conversion factor. Precise unit conversions, which are not instant mental math, are covered in the other section. The sections have different goals. The reason the least accurate mnemonic ("1 μm is approximately half a tenth, or 50 millionths") isn't more accurate is that half a tenth (often expressed as 50 millionths) is the closest landmark that means something to the machinist's gut instantly. "3.937008e-5 inches" may be more accurate, but it means nothing to your gut instantly. You "translate" the latter to "feel" it mentally; the former is "palpable" as-is. Meanwhile, as for "a tolerance of ±0.25 mm is about the same as a tolerance of ±10 thou"—that's both useful to the gut and also so accurate that the last 2 tenths are nearly meaningless. If they gave you a tolerance of ±10 thou, then you shouldn't be on the edge at 9.8 thou arguing about whether the last 2 tenths matter; if you are, then "you're doing it wrong", with "it" referring to your setup, tooling, or operating in general. Not that those 2 tenths are legally negligible—legally, at receiving inspection, you either are less than 10 thou or over it. But the point is, can you teach a student to feel that ±0.25 mm is about the same as ±10 thou, as opposed to ±2 thou, and to know in the gut upon first glance at the drawing, hey, this is a different animal regarding operating and inspecting? With the first one, the resolution of my caliper (half a thou) doesn't matter (I'll check periodically to confirm I'm staying well inside—whether it reads .0035" or .0045", either way I breeze right past it). Whereas with the second one, the resolution alone may trample both sides of the borderline between good and scrap, and I better carefully measure every third piece with a tenth-reading mic, instead of breezily measuring every 10th piece with a caliper. I better check the mic against a gauge block repeatedly throughout the day (whereas for the caliper, meh, I just confirmed that .250 drill this morning, it read .249—I have no doubt the drill and the caliper are both still good enough, we're not going to inspect closer to find out where the other thou went). — ¾-10 03:36, 24 September 2014 (UTC)
thread_title:  Edit of Mnemonics