Tap And Die Questions

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bosephus

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hi guys and gals

i have a project coming up that i need to buy a tap and die for , i normally would just single point the threads
but in this case due to extremely high material costs ( many hundreds of dollars ) i feel that it would be better safe then sorry and invest in a high quality hss tap and die to take as much risk out of the equation as possible .

so what i need to do is tap a hole .850X20 tp 2.450 inches deep to a shoulder and the corresponding threads on the mating piece .

so my questions are ,.... tapping to the shoulder ,.. do i need to start with a taper tap and then switch to a bottom tap , or can i just use a bottom tap from start to finish .

and what brands to look at and who to buy them from , this is most definitely a case of wanting quality versus a price point
 
Best to start with a tapered tap, then go to a bottoming especially for that depth. Can't say I have a preference for what brand, as long as it is HSS.
 
Always use a taper or at least a plug tap first, then go to a bottoming tap. Get Emuge or OSG, something like those premium, specific to your material.
 
A tap and die for ".850X20 tp 2.450 inches deep" will need to be custom made. It will not be cheap, and it might take a while to get it in your hands. It will also not make a full thread all the way to the shoulder.
 
If you are tapping a blind hole, the best tap would be a spiral flute tap, they only come in taper (or is it bottom) configuration, and are best used in a tapping head, not by hand. .850 by 20 is nowhere near a standard tap, so you could specify the length of the tap as well as the diameter and pitch when you ordered it.
 
The spiral flute taps come in bottoming and modified bottoming styles.
The modified bottoming style I believe has a 1 or 2 thread lead whereas the bottoming has no lead to speak of.
 
Size is an odd one, unless the male thread is an undersize slightly worn 7/8-20? Single pointing wouldn't be the easiest that small that deep, but doable.
 
bosephus said:
so what i need to do is tap a hole .850X20 tp 2.450 inches deep to a shoulder and the corresponding threads on the mating piece .
Click to expand...
Where exactly do expect to buy such taps and dies? This is exactly where single point threading shines, one may make whatever thread their machine will allow.
 
If that is truly the size, you could certainly make the tap starting as a plug tap and then grind off the end of the tap as you reach the end of the thread, allowing your to form threads right up to the shoulder.

Jim
 
+
.850-20 --- I can't find that thread tap anywhere. Custom will cost you big time.

"Billy G"
 
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