hole size for taps

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On Sunday, January 19, 2014 7:32:01 AM UTC-8, DerbyDad03 wrote:


Being too lazy to go in the house to look it up on the 'net I take a short cut.
I open my drill index and look at the chart imprinted on the dill holder.
Harry K
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wrote:

Works if you have a half decent drill index. The cheapassed drill sets half the guys on here have are doing good to have the DRILL size stamped in a readable form.
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On Sun, 19 Jan 2014 07:11:42 -0800 (PST), jamesgang

But I always misplace my jeweller's loupe, so half the time I can't read them - - - -
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wrote:

From sci.eletronics.repair group, useful to know tidbit:
Mark Storkamp        Oct 9, 8:47 am
- Show quoted text -
For any size thread you plan to tap, to find the hole size just subtract the pitch of the thread from the diameter of the thread. For an M3x.5 that would be 2.5, for a 1/4-20 it would be .25-1/20, .25-.05, or .2 (#7 drill is .201), etc.
also I have four pages of tables metric-fine <http://www.coasteltools.com/tech_tap_drill_mf.htm
metric-coarse <http://www.coasteltools.com/tech_tap_drill_mc.htm
National-coarse <http://www.coasteltools.com/tech_tap_drill_nc.htm
National-fine <http://www.coasteltools.com/tech_tap_drill_nf.htm
don't know if they still exist, though
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On 01/19/2014 06:08 AM, herb white wrote:

I like this one:
http://www.physics.ncsu.edu/pearl/Tap_Drill_Chart.html
Jon
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That's a nice link. It includes the chart I linked to as well as a few other useful charts.
Here's another chart that I have hanging next to my drill press. It comes in handy every now and then...
http://images.meredith.com/wood/pdf/drill-press-speed-chart.pdf
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On Sunday, January 19, 2014 8:08:32 AM UTC-6, herb white wrote:

Just for the sake of saying it, There is a good APP for I-phone called Drill Chart. Covers Metric and American. I use it almost every day at work.
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On Sun, 19 Jan 2014 06:08:32 -0800 (PST), herb white
Lots of them online - or do the simple calculation - nominal diameter less .75Xpitch is a good rule of thumb. so a 1/4X20 gets ..2125 - the tables say.2188 for 50% thread 1/2X20 would be .4625 - tables say .4688 for 50% thread (iron and steel). For plastic or brass the book says .4531 (75% thread).
BUT - you obviously have a computer with internst connection so just google "tap drill size" and print off the chart.
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