Tap/die drill sizes?

[rsmith]

I'm sure this has been posted before, but I can't seem to find anything Is there a guide chart that will show basic tap sizes (metric preferably) and the correct drill bit to use in conjunction with them. Also, the best tenon size to use with each die size? I have been experimenting with my "el-cheapo" HF 40 pc. set and am having too many cracked/unusable test pieces just "eyeballing" my starting points...I saw a post explaining taking the size and subtracting the pitch, or something like that. Being totally incompetent on taps and such, say for example I'm using a M10x1.25 tap, what numbers are what? Using the subtraction method, in this case what would be the correct drill size? would that be 10mm minus 1.25mm, or approx 8.5-9mm bit, or am I WAY off? And for that same example, what would be the best diameter tenon to use the corresponding die with? Sorry for the seemingly basic question, I have put off dealing with this as long as I can, but now I'm finding some ideas just can't be executed with using premade threads from leftover kits parts without more modification of them than I am willing to do
thanks

 

[skiprat]

'Theoretically' you simply deduct the smaller number from the bigger one to give your drill size. So in your example...M10 x 1.25mm you would choose an M8.75 drill. ( I've never seen metric drill with smaller steps than 0.1 so you need a M8.7. Drills always drill bigger than their size so that should be fine. Yo will often end up with a different sized hole in different material.

Similarly with the die, you would have the item turned to 10mm and just have a slight chamfer to assist the first cuts.

Success with taps and dies has ( in my opinion ) got more to do with how the tool is offered up to the work. If you have a proper tap / die holder and are doing it on the lathe this shouldn't pose any problems.

Tap and die holders are actually pretty cheap concidering.
If you want a pic of how I hold taps and dies, then let me know and I'll post a pic or two

 

[rsmith]

While I know there are hundreds of "right" ways to hold and use, I would love to see your setup Steven. Along with a few others posts on here, half of what I have learned about straying from "kits" has been just from studying some of your photos and figuring out how I can adapt it myself, so yes, photos=good, if you have a chance:good:
Thanks

 

[skiprat]

The first and second pic are tapping, using a spring loaded tap guide.
A very cheap little gadget. The point of it sits in the dimple in the back of the tap. Here I'm using a T bar wrench. If the tap didn't have the dimple then I'd use a collet type tap wrench which does have a dimple in the end. The problem with taps without these little holes in the end means that space is used up real quick. I try to avoid the taps that have the little square pyramid on the ends. Of the hundreds of taps that I have, all the best quality ones have a hole in both ends.
The last pic is the die holder. These often come with the ability to hold three different diameter dies. It has a morse taper to fit in the TS.

 

[rsmith]

Thanks for the pictures, this is a huge help

 

[randyrls]

I'm sure this has been posted before, but I can't seem to find anything Is there a guide chart that will show basic tap sizes (metric preferably) and the correct drill bit to use in conjunction with them. Also, the best tenon size to use with each die size?

Rob; This is a complete set of both metric and Imperial tap and die drill sizes. Check out the rest of the site. It has a lot of good information.

http://www.littlemachineshop.com/Reference/tapdrill.php

 

[rsmith]

Randy, this is perfect, thanks for the link