Tapping 1/2-13 and 3/8-16 deep holes in 6061

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RJS100
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Tapping 1/2-13 and 3/8-16 deep holes in 6061

Post by RJS100 »

When I first started tapping holes I bought a few taps that I learned later were not great for aluminum. This is the series of taps I am referring to:

https://www.amazon.com/gp/product/B00F8 ... UTF8&psc=1
https://www.amazon.com/gp/product/B00F8 ... UTF8&psc=1

The taps are similar, but the 1/2-13 has an h3 tolerance and the 3/8-16 has an h5.

Since I almost always use metric taps, I did not replace them. Today I tapped two 1-inch-deep holes. I used a 1/2-13 and 3/18-16. Here are the details:

1/2-13, 700 rpm, .33-inch peck cycle
3/8 - 16, 800 rpm, .33-inch peck cycle

In addition to mist lubrication, I also put some A-9 on the tap and the holes. When I tapped the 1/2-13, the mill stalled after the second peck cycle. The 3/8-16 tapped ok, but it looked like the mill was struggling. It even looked like it was struggling to pull the tap out of the hole. It just didn't look smooth. The mill has the ability to produce significantly more torque than required to tap either of these holes. Strangely, I have tapped half inch deep 1/2-13 holes before with this tap and speed/feeds.

Do you think I need to tap at a higher speed. Are these taps crap! Is there something else going on here?

Thanks... Richard


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