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Speaking of drill bits, here's something I'm wondering about: I used Marv's formula to figure the DOT at 65% for a 4-40 tap. If my figures were right, it came out to about .0910. So a #43 @ .0890 was about .020 to small and a #42 @ .0935 was about .015 to big. However, a 2.3 mm @ .0906 was "just right". So that begs the question of whether mm bits are sometimes used to bridge the gap between numbered bits or am I tuned into my own "fairytale" here?Jim
Quote from: Flyboy Jim on March 14, 2016, 01:53:11 AMSpeaking of drill bits, here's something I'm wondering about: I used Marv's formula to figure the DOT at 65% for a 4-40 tap. If my figures were right, it came out to about .0910. So a #43 @ .0890 was about .020 to small and a #42 @ .0935 was about .015 to big. However, a 2.3 mm @ .0906 was "just right". So that begs the question of whether mm bits are sometimes used to bridge the gap between numbered bits or am I tuned into my own "fairytale" here?JimYour math is a bit off, by a factor of 10. A #43 and #42 differ by only 0.0045" and the hole size actually made by drills can vary from -0.001" to +0.003". Larger number and letter size drills have greater difference in size, but they also have a wider tolerance for hole size, and the diameter for tapping is not as critical.If you drill slowly or allow a drill bit to spin in a hole, it will tend to open it up by a couple thousandths, due in part to expansion from heating, and perhaps more because of runout, flex, and vibration and the side cutting action of the margins on the flutes.
Jim,By now you've learned that any time you report a calculation in a thread it's a good idea to check it on a calculator. I'm reasonably good at mental arithmetic and I still do that, just as I check myself on a calculator in the shop where an error can have more serious effects.Nevertheless, your original question is a good one. When you use my DRILL program to find the drill closest to an input hole size, it reports the closest as well as the two smaller and larger than the closest along with their difference from the desired size. For example(2.20 mm) with size 0.0866 (-0.0044)(2.25 mm) with size 0.0886 (-0.0024)(43) with size 0.0890 (-0.0020)***** (2.30 mm) with size 0.0906 (-0.0004) *****(2.35 mm) with size 0.0925 (+0.0015)(42) with size 0.0935 (+0.0025)(3/32) with size 0.0938 (+0.0028)As you can see, it includes metric size drills. A well-equipped shop should have a set of metric drills not just for this application but for dealing with metric machinery and metric threads.
and let Carl have his thread back!
Back from a business trip to Canada.Had to drive via Rochester, New York.I could have sworn I caught a whiff of mint chocolate cookie.I must have been real close to cookie-land...and its crumbs. Good to be home. Now I have a whole lot of catching up to do.
Should have let me know you were going by, would have handed you a bag of cookies on your way by!If you came up to Rochester and caught the Thruway over to Buffalo/Canada, you were only a couple miles away. Oh well, have to eat your portion for you...
Quote from: crueby on March 17, 2016, 08:54:10 PMShould have let me know you were going by, would have handed you a bag of cookies on your way by!If you came up to Rochester and caught the Thruway over to Buffalo/Canada, you were only a couple miles away. Oh well, have to eat your portion for you... Best be careful with the offers there my friend.I suspect I'll be making that trip again (assuming I last long enough at my job).In the meantime...enjoy my cookies. It wasn't until I was going through that area that I realized you might be close by.If the opportunity comes up again I'll PM you.(I try not to let people know on the forum when I'm on a trip. I don't so much worry about bad people. It's the pranksters on this forum that are the danger. I won't name them. I'm sure I needn't have to.)Oops. Did I end that sentence correctly?Initials are A, B, C, ... you get the picture.
Your cookies passed the QA test. Forgot to log the results, so had to retest with more. Yum.
I've just jinxed myself, haven't I?Where's my lucky 'knock on wood' piece of wood?Drat. Lost it. So unlucky.
Quote from: zeeprogrammer on March 18, 2016, 09:56:40 PMI've just jinxed myself, haven't I?Where's my lucky 'knock on wood' piece of wood?Drat. Lost it. So unlucky.You ain't lost it friend! It's parked right thar 'tween yer ear bones!!