| Gallery, Projects and General > How do I?? |
| The size of drill? |
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| ieezitin:
Saw When I am not sure I Use the .9742 ratio. It’s not dead balls on like shown on all the charts, but a few 10ths of a thou don’t bother me that much. It certainly works. Divide .9742 by the thread pitch. Next subtract your answer from the tap diameter this will give you the tap pilot drill size. Example. ¼-20 bolt. Divide .9742 by the pitch 20 and you get .0487 Now subtract .0487 from the diameter of the tap .250 You get .20129 this is your drill size. Remember stainless, cast, aluminum are percentage slightly different, so apply as necessary. This will always get you in the ball park. Hope this helps. Anthony. |
| mklotz:
.9742/0.013 = 75% so that is the rule I showed but adjusted for 75% depth of thread rather than the 77% one gets using "1" in place of "0.9742" |
| andyf:
i Saw, Here's another table, showing the metric tap drill size as 2.65mm for 5-40 UNC: http://mdmetric.com/tech/thddat9.htm#uc That just leaves you with the problem of finding a 2.65mm drill. Andy |
| kvom:
My drill index box has the tap/body drill sizes for most common imperial threads written on the box lid. Very useful. |
| saw:
Thanks folks no I think I kan manage it. :thumbup: |
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