Pilot Hole for Threading

Spiral point otherwise known as gun point taps are my favorite for all thru holes. Even for a blind hole I will drill extra deep to allow extra room for the chips. If I really need thread to the bottom of a hole then I will use a spiral bottoming tap after tapping as far as possible with a gun tap.
After using a gun tap in a blind hole you can pick out the chips to clean out the hole.

ChazzC said:
Also why I mark stock when I “obtain “ it. Which reminds me, I need to find a chart of the colors they use to mark rod stock.
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I found out the hard way that not all suppliers use the same color code for material.
 
I found a Whitney I have had maybe 30 years. My brother in law worked in a factory that sent 55 gallon barrrels of bits and taps to scrap. He brought these home.
 
benmychree said:
5/!6 is the proper size for 3/8-16, it is likely that your tap was simply dull, hence the tight fit. Likely it was a carbon steel tap, not HSS and it would not tolerate harder materials.
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Well, it started out as a Craftsman.
 
Flyinfool said:
And since it is just a ball detent that will never have a significant load on it you could even go a bit bigger than the "Q" IF it is still tight, you could try a "R" / .339 or even an 11/32" / .343.

If you have a good tap the "Q" should be fine.

It is rare that you will find a good tap at a hardware or big box store. Craftsman never had good taps.
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I have their big set I bought in 1987 IIRC, back when I didnt know any better for working on cars. For chasing threads their fine, for tapping mystery metal, not so much.
 
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Flyinfool said:
Spiral point otherwise known as gun point taps are my favorite for all thru holes. Even for a blind hole I will drill extra deep to allow extra room for the chips. If I really need thread to the bottom of a hole then I will use a spiral bottoming tap after tapping as far as possible with a gun tap.
After using a gun tap in a blind hole you can pick out the chips to clean out the hole.


I found out the hard way that not all suppliers use the same color code for material.
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Yes, so far that is what my search for charts is showing – glad I either label or mark the ends.
 
For unobtanium, and Dave having it, you have to remember he is a secret squirrel, or from skunk works....
 
Try the Guhring tap drill charts they are my go-to for all general tapping since they show the common drill sizes for whatever percentage of engagement you want. I like these better than the online calculators:


I also like to use form taps in aluminum. They have a very well set up chart for that too which is also insanely handy for choosing drills for form taps:

 
Had the lathe since January, but now have my 1st usable part. Drill arbor for a hay sampling tube. And the Q drill bit worked fine. Thanks.
 

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You know I have a bunch of bags of high quality used taps (Emuge, Yamawa, OSG) for not much money...
 
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