Originally Posted by
LeeWay
Percent of thread is just like it sounds. Percent of possible thread profile.
I am not even sure you could use 100% threads on both the fastener and the hole. I think that might be called "Welding".
It would certainly make for a lot of friction. Unnecessarily.I get away with 50 to 55% threads most of the time. I like more thread in my aluminum parts though. 75%.
Here is a chart that I like to use.
Supplies
It works great for rigid tapping and coolant and also works well for all my parts.
That is one nice thing about rigid tapping that isn't that obvious. There is not jerking. Smooth in, smooth out. Nice.
Lee,
I'm interested in the 75% you use on aluminum. Are you using 75% with one of these tapping heads?
Here's why I ask. I have one of these tapping heads, and haven't used it yet. The reason why is yesterday I hand tapped about 10 or so holes for a #10x32 fastener. I used a #21 drill, which according to your chart is 75%. Like always, I had to reverse direction every 1/4 - 1/2 turn to free the material or I would have broken the tap. Looking at these videos using tapping heads, it only reverses when it is finished with the hole. How is it that with a tapping head you can get by without reversing direction during the tap, but with hand tapping you cant?
Scott...
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