Forming tap

I was rummaging through my tap collection and came across a couple of forming taps. I have no idea how they got there, but there they were.
Now, the question is: where are they better used than cutting taps? Since they are more particular about the hole size, I won't use them unless they have some advantage.
Thanks, Bob
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Stronger threads in aluminum...
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On Sun, 19 Mar 2017 18:38:43 -0400, Bob Engelhardt

Greetings Bob, Form taps make a stronger thread in materials that are fairly ductile. So for example, wrought aluminum aloys, mild and stainless steels, and some copper alloys. It's a little scary but I have form tapped thousands of 10-32 holes in 304 SS. You need to pay attention to how many holes have been tapped so that the tap can be changed before the torque gets too high and the tap breaks. Free machining brass is not a good material to form tap because it is kind of brittle, but silicon bronze form taps well. When tapping blind holes form taps are nice because there are no chips to worry about. They are especially good when the max length thread is needed in a blind hole. I use form taps as much as possible in my shop. Eric
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On Sunday, March 19, 2017 at 8:05:49 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

I use form taps

I have no experience with form taps, but I have the impression that they last longer than cutting taps in some metals. Is that right or am I wrong?
Dan
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Dunno, but I've retired several #10-32 spiral point taps after 1000 holes tapped freehand with a Milwaukee reversible drill in 12 Ga CRS. They were the panel mounting holes in custom welded relay-style racks, ~ 60 panel mounting holes per rail so 8 bays per tap.
-jsw
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wrote:

I got a 6061 aluminum part back that the shop had form tapped in holes that were apparently too large, so the tap left a second false thread groove between the real ones that a screw could engage. They were small screws, #3 or #4 IIRC, and the torque difference wasn't all that noticeable at first. -jsw
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    Blind holes is one example, as they don't form chips which need to be cleared out. Just make sure that the tapping head stops before they bottom out. :-)
    Your workpiece should be a fairly ductile metal, of course. Forget about tapping hardened tool steel -- but then cutting taps don't do to well there, either. :-)
    I've even used them in Teflon, where the material expands to grip the screw once it is in place.

    Be sure that you use the right hole size. You can look it up in a table in _Machinery's Handbook_, or in certain machinist's calculators.
    Enjoy,         DoN.
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I wonder how forming taps would work in punched holes to maximize the amount of thread created.
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On Monday, March 20, 2017 at 3:44:35 PM UTC-4, Bob La Londe wrote:

In interviews with many tap manufacturers, I've always heard them emphasize the importance of hole accuracy for thread-forming taps. It sounds unlikely that punching holes would be a reliable way to do it.
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snipped-for-privacy@gmail.com wrote:

We have progressive dies at work that use them. The main advantage there are no chips to deal with. The punches are sized per tap requirements. This means we get less engagement at the bottom (in the punch blowout). The bolts are not under high stress so we are not worried about striping out.
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On Friday, March 24, 2017 at 7:11:56 PM UTC-4, Stephen B. wrote:

I'm sure that if you have properly-sized punches, you can do it. It sounds like a production thing, though, that would take a few trials to get it right.
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On 25/03/2017 10:26 AM, snipped-for-privacy@gmail.com wrote:

Shouldn't be a big deal. Holes come out pretty much to the punch size, so likely just need a custom decimal size punch, I'd think. Pretty sure I watched a YouTube video of a punch press that could produce a bit of an extrusion, offering more material for threading.
Jon
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Phil, Eric, & DoN -- thanks. I'm curious enough to get the drill I need (#16 for 10-32) & try it.
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    My lookup shows 4.4mm (usually metric sizes for roll taps for imperial screws. That works out to 0.1732", while the #16 is 0.1770" so the thread will be a bit poorly formed.
    Good Luck,         DoN.
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On 3/21/2017 12:11 AM, DoN. Nichols wrote:

Ummm ... these are Balax taps and this Balax page shows that a .177 drill will give a 70% thread. http://balax.com/products/thredfloers/12288-000
I'm not used to thinking about threads in percentage terms, but 70% sounds pretty good to me.
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On Tue, 21 Mar 2017 00:58:18 -0400, Bob Engelhardt

70% will be plenty strong enough. If tapping punched holes in fairly thin material you can get away with a slightly undersized hole because the metal will just extrude away from the material surfaces. Remember that a high pressure cutting fluid is good to use because the thread is being formed. Eric
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On 3/19/2017 6:38 PM, Bob Engelhardt wrote:

I used them for threaded arbors on mini-grinder cup brushes. They take two to three times the horse power but no chips. They always tell you when they are too dull....SNAP!
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