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Thread: Tapping Drill Chart
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25th Sep 2018, 07:07 PM #1Most Valued Member
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Tapping Drill Chart
I have a copy of the Engineer's Black Book. It has tables with tapping drill sizes for most of the thread standards. There are two problems with it. Firstly, the text is too small for my ageing eyes. Secondly, all the tapping drills sizes given are for 77% thread engagement. If you want the size for a different % engagement you need to use the formula given. I decided to make a table for the metric sizes a hobbyist might use for various % engagements.
It's much easier to read. And as I don't have every drill size made, it allows me to work out how much thread engagement I will get for the drill size I do have on hand.
I hope someone finds it useful. If you would like any extra info added to the table, let me know and I'll see if I can oblige. I'm working on a UNC and UNF version too.Chris
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25th Sep 2018, 07:16 PM #2Pink 10EE owner
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For metric threads I always use hole diameter minus thread pitch equals tap drill.
Gold, the colour of choice for the discerning person.
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25th Sep 2018, 07:25 PM #3Member: Blue and white apron brigade
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Get yourself an ecopy of the 100 page, Workshop practice Series #12 by Tubal Cain. "Drills, Taps and Dies" . The Appendix has about 10 pages of easy to read, drill sizes and thread engagement charts in the back for all types of threads.
[QUOTE]For metric threads I always use hole diameter minus thread pitch equals tap drill.[/QUOTE]
According to the ISO Metric formula this approach will give >85% thread engagement.
This can be hard on taps and hands especially in harder materials, even when using a good lube.
Eg M10 1.5, would work out to be a drill size o 8.5, whereas I typically use 8.8mm for a 75% engagement which will work for most things I do. When I made my DP table with the 25 x 5/16" holes I used a 0.1mm larger drill than recommended which produced 70% engagement. Those thread/holes are 20 mm deep and that's plenty of thread @70% to clamp down objects.
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25th Sep 2018, 07:36 PM #4Most Valued Member
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25th Sep 2018, 07:47 PM #5Most Valued Member
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25th Sep 2018, 07:55 PM #6Member: Blue and white apron brigade
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That is closer to Bolt Thread engagement, which is slightly different to Nut thread engagement. The Tubal Cain books gives both and specifies an approx average biased slightly in favour of the Nut thread engagement.
In the Tubal Cain book 8.8 mm will produce a 77% nut thread engagement and 66% bolt thread engagement for an overall effective engagement of 75%.
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25th Sep 2018, 08:31 PM #7Most Valued Member
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25th Sep 2018, 09:25 PM #8Most Valued Member
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This web based calculator gives exactly the same numbers as my table. OSG | Taps | End Mills | Drills | Indexable | Composite Tooling | Diamond Coating | Die Products
Chris
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25th Sep 2018, 10:11 PM #9Novice
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Chris, thanks for going to the trouble of posting your guide. I have others, but the extra info in yours will be very useful!
Much appreciated
Michael
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25th Sep 2018, 10:59 PM #10Senior Member
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I've made up THIS table for work, I printed it on 4 A3 pages and I carry a copy around on my phone for quick reference. It doesnt have your % engagement request, but some people might find it handy. It covers metric, fractional inch, decimal inch, gauge / letter drills, metric coarse and fine, UNC, UNF, UNEF, BSW BSF from 0 through to 1 inch.
If anyone has a suggestion for more detail that would suit my table though, feel free to point it out.
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26th Sep 2018, 04:40 AM #11Senior Member
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Chris thanks for sharing your chart.
In this day and age I tend to use one of the online calculators or an app for the phone to look that kind of info up. I don't have the smarts to calculate my own. Easier to print the chart from the magic box. One example. Theoretical Machinist
Pete
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26th Sep 2018, 09:20 AM #12Most Valued Member
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Thanks Pete. The online calcs/apps are great, but I tend wear gloves in the workshop (I know, I know!) and I have to remove them to use the phone. Plus I don't like greasing up my new iPhone. My dream is to have a dedicated iPad mounted to the workshop wall for just this purpose, but that's an expensive option. My old surplus iPad wont run the latest OS sadly.
Chris
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26th Sep 2018, 09:52 AM #13Member: Blue and white apron brigade
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26th Sep 2018, 10:26 AM #14Most Valued Member
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26th Sep 2018, 07:44 PM #15
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