We use thread forming taps, no chips. One tap lasts for thousands of holes in 6061. Most of the time it's 10-24.
So far, my experience with spiral flute taps hasn't been great; they just seem to be too fragile, even in aluminum. Obviously, very desirable for getting the chips up and out the top of a blind hole. Have a job coming up (CNC with rigid tapping) that is 10-32 with 1-inch deep thread in a blind hole (Lots of them, in Aluminum). Most of my bad experiences breaking these are power tapping in a Bridgeport, but... Have never had any problems 30+ years with 2-flute spiral point, but tired of digging chips out of the hole. Worried about using spiral flute on this job.
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We use thread forming taps, no chips. One tap lasts for thousands of holes in 6061. Most of the time it's 10-24.
Jim Dawson
Sandy, Oregon, USA
1” deep is pretty deep for #10, does the entire depth need to be threaded?
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OSG Hypro NRT list 14001. I just did a job thread forming 10-24 X 1" deep in aluminum, did 3000 holes with 1 tap.
You can do a couple things.
Spiral flute taps are by nature weaker than straight flute. More material has to be ground off the tap to achieve the spiral fluting.
What I have done with acceptable result is to open up the minor. For example a 4-40 I'll have the minor at 0.093". It passes inspection and puts the least amount of stress on the tap.
Thanks for the input, guys. Yeah - I don't know why somebody would spec a #10 hole with threads 1 inch deep. I'm just doing what the customer's print says.
So, I decided I needed to try forming/rolling for the first time, and just got home from doing the first test piece a few minutes ago. Wow - that's awesome. I started with the larger of two recommended drill sizes. I can see that the top (minor diameter) of the threads isn't quite closing as far as it could/should. When I get back to it in the morning, I'll go one size smaller and everything should be fine.
Forming taps are excellent for deep threads in modestly hard materials.
Coming from an engineering background, there are a few designs that justified unusually deep threads. All the machinists would whine and complain that the engineers are idiots of course. In the end, I would actually machine the prototypes myself to prove it was not only possible, but easy. Easier than complaining about it anyway, lol.
For harder materials, peck tapping and thread milling got me through a few challenges. Step drilling has also helped which yields a hole with starting threads at about 55% and bottom threads at about 75%.
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