Saturday, April 11, 2015

Metric Over - Under Drill set for Fractional sizes

As we all know the nonsensical Number and Letter drill system is woefully inadequate for the proper Over - Under drilling. It doesn't matter how, why, who, or where this systems came from it needs to be replaced.

Previously I posted my "Reverse Look Up Chart" and have now added some changes to what has become the only chart I go to when sizing for any of the custom work I do. Again, what I like about this chart is the ease and speed with which one can make a decision for hole sizing. After measuring any shaft, pin, or dowel, you get to look at the exact number that you measured and see what is above and below AND by how much without getting out the calculator.

I would like to challenge any drill manufacturer to package the minimum set of Over - Under drills for the fractional sizes. There are more variations too; like tap sizes that are logical and reamer under size too.
The idea is to use existing Metric sizes at the 0.1 and 0.05 size series to create the perfect (minimum) Over - Under drill set that I can reliably go to and instantly/easily grab the a drill that is always the same amount Over or Under

The chart highlights in blue the 0.002" or 0.003" over and under METRIC drills.
What the chart I made also illustrates are great holes or gaps around the fractional sizes that results from using only Number & Letter sizes. Some of the Number series happen to be spot on the Metrics and that is fine but what about the large gaps?



Most drill charts show only the decimal next to the the drill, This makes for a lengthy research project every time you go to make a new decision when choosing a drill. Also it does not show or emphasize the random gaps between them.

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