Those Drill Index Numbers

[rgsparber]

My old eyes were having trouble seeing the raised black numbers on a black background inside my drill index boxes. My solution is so embarrassingly simple; I hesitate to publish it.

If you are interested, please see

https://rick.sparber.org/DrillIndexNumbers.pdf


Your comments are welcome. All of us are smarter than any one of us.


Thanks,

Rick

[mklotz]

An additional tip for future readers...

For the numbered drills, put a spot of white paint every five drills, then red paint every ten drills. Makes it easy to count to the correct drill without squinting at the numbers. Sharpie paint markers are handy for this sort of color coding of tools.

Can you believe that we Usonians are still struggling with three idiotic drill nomenclatures...

Letters - no indication of size, nomenclature closed at both ends
Numbered - no indication of size, counterintuitive numbering (drills get smaller as numbers increase), closed at one end
Fraction - how many people can mentally calculate the drill one size smaller than 19/64 ?

The drill nomenclature alone should be a decisive argument for adopting, at minimum, metric nomenclature for everything.

[Crusty]

I always put my calipers to a drill before drilling because often they aren't the size marked, except for my Latrobe drills.

[DIYer]

Thanks rgsparber! We've added your Drill Number Visibility Modification to our Miscellaneous category,
as well as to your builder page: rgsparber's Homemade Tools. Your receipt:

Drill Number Visibility Modification by rgsparber

tags: marking, drill bit

[old kodger]

I always put my calipers to a drill before drilling because often they aren't the size marked, except for my Latrobe drills.

Me too, I have a metric son, so no matter what the actual size he always presumes it to be some metric size or other.
I actually had a young (I suspect straight out of school) shop assistant in a nut and bolt store ask what was the metric equivalent of 7/16 bsf, on the basis that he had no idea what bsf was.

[Crusty]

I use both systems and my builds tend to have a mixture of screw sizes depending on what fasteners I had in stock that would work. I bought a calculator to do conversions for me but it's faster and more convenient to use my cheap calipers that do the conversion with a push of a button. When I go to work on one of my builds I always grab red and yellow sets of allen wrenches as well as a Crescent wrench and most of the time that's enough. I also keep a cheap plastic screw thread identifier in the top of my toolbox so I can quickly know what thread I'm working with.

The English system of thread pitch identification is better than metric for me because I can quickly count how many threads there are in 1" versus trying to get an accurate measurement between adjacent threads in the metric system.

[rgsparber]

Although I keep all drills in their original index boxes, I have one table, listed in decimal inches, of all families of drills. It also tells me the correct tap and clearance holes. I tap at 55% engagement:

https://rick.sparber.org/drillTableW...learance10.pdf

Rick

[mklotz]

Like you, I keep the drills in indices but also have a chart showing them in order of size. I interspersed the metric drill series as well since sometimes one can get closer to a desired hole size by using a metric drill.

My DRILL program uses a data file which lists all the drill series in non-interlaced form; when the program runs it performs the interlace. Since the data file is in ASCII form, the user can easily modify it to contain only those drills he has so, when searching for a drill for a desired hole size, the seven values returned (three nearest smaller, nearest, three nearest larger) are all in his tool chest.

[Crusty]

I use the 50% range too except for aluminum and then I thread in the 75% range, but I prefer to install helicoils because aluminum threads aren't long for this world. There's a handy chart available for download at Little Machine Shop for Imperial and Metric threads with all the pertinent dimensions.

[mklotz]

And when the chart to hand doesn't cover the job to hand, use the formula

TD = MD - (DOT/75) / P

where:

TD = tap drill needed for DOT percent threads
MD = major diameter
DOT = percentage thread desired
P = thread pitch expressed in tpi

Example:

1/4-20 55% thread

TD = 0.25 - (55/75) /20
TD = 0.2133... = #3 drill

It should be obvious that for 75% engagement, the typical value, the formula reduces to the simplified form taught in many shop classes...

TD = MD - 1/P

Since metric threads have 60 degree form same as inferial, the same formula can be used for metric threading with only minor adjustments

TD(mm) = MD(mm) - (DOT/75) * P (mm)