For the manner in which men live is so different from the way in which they ought to live, that he who leaves the common course for that which he ought to follow will find that it leads him to ruin rather than safety.
-Machiavelli

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Thursday, April 9, 2015

A Common Misconception About Taps

Let's take care of this once and for all: the difference between "gun" taps and standard taps.

On the left a standard fluted tap. On the right is a "gun" fluted tap. You will notice that the gun tap has an additional section ground away near the tip. That grind has a very specific purpose: it turns the chip around and forces it down. Standard taps move the chips up.




A gun tap as it exits a through hole. Notice the way that those chips are going.
Here it is, short and simple: gun taps are intended for through holes. When tapping a through hole with a gun tap, the chip is turned and sent down through the hole and out the bottom. This makes the entire operation easier because you are not working against the chip. However, when you use one in a blind hole, the chips will be forced into the bottom of the drilled hole and basically fill the hole you are trying to thread.

Tapping with a gun tap is typically easier since you are not trying to work the chip up through the flutes. I think that is why people like them. As long as you have a deeply drilled hole, and don't mind a bunch of shavings being compressed into the bottom, I suppose that's alright. But we all know it's WRONG!

If I could only fill my tool box with one type of tap, it would be standard. Why? Because a standard tap doesn't care if the hole is blind or through. The gun tap is meant to work with only one type of hole.

I doubt I will EVER get done explaining this to people.

2 comments:

  1. Something I didn't know. For blind holes I have always used a bottoming tap.

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    1. You are correct, Ralph. You always want to run a bottoming tap if you want the threads to get close to the bottom of the hole. It's just that I know and work with many people that are confused about the actual purpose of different taps. The gun tap is probably the most misused of them all. If I start a hole with a gun tap and attempt to finish it with a bottoming tap...I will just crush the chips further into the bottom of the hole. At my job, for instance, our cutting tools are restocked by a service. The ONLY taps that they stock in our tool room are gun taps. Wrong answer in my book. Just goes to show ya!

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