Turning down tap shank success

I have had to relieve the diameter of tap shanks many times in order to tap deep holes or to cross a bore and the like. This morning I
needed to reduce the shank of a 5/16-18 tap. The job required that all but about 3/8" of the shank diameter needed to be turned down. This meant that in order to do the turning in one chucking the end of the tap needed to be supported. The tap in question was a spiral point tap. So I used a live center for support. I put a .25 thick piece of aluminum between the point of the center and the tap. Then, with the spindle turning, I cranked the tailstock quill forward until the center and the tap points had both made pretty deep depressions in the aluminum piece. I used a coated threading insert to turn down the tap. 255 RPM and .004" feed. The material was removed in one pass. I plunged the tool into the work where the cut would not be an interrupted cut. Then fed away from the chuck by hand to remove the incomplete threads. This part of the cutting was an interrupted cut so I wanted to feel the cutting. After removing the incomplete threads the cut was reversed so that the tool was feeding towards the chuck. The operation worked quite well and the threading insert still looks good. HSS taps are hard but coated carbide is much harder. Eric
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On Saturday, August 25, 2018 at 2:09:52 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

Nice turning, Eric. My world is somewhat made of custom modified tools. But were you holding your breath while doing this?
I'm currently in the Sun Valley Idaho area for work, and the smoke from var ious forest fires is pretty horrible. I've been here a couple of times befo re and I know there have been days in the pst week when the visibility is w ay below five miles. Today was pretty good, though, and I got in some good views of mountains and wildlife.
I understand though that up in your neck of the woods, it's really bad. are people doing anything different to cope with it? I was surprised here that there aren't people wearing at least particle masks - my mouth has taste l ike smoke for a week.
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On Mon, 27 Aug 2018 21:01:21 -0700 (PDT), rangerssuck

Yeah, the smoke here has been really bad. Lotsa folks suffering because they already had lung issues, like asthma and the like. Today is the fisrt on a long time that the air smells OK. Nevertheless when I look toward the horizon the air is still hazy. Eric
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On Tue, 28 Aug 2018 08:29:22 -0700, snipped-for-privacy@whidbey.com wrote:

My buddy is living in the Twin Falls area and said the air is clean right now, but the fires are farther off than here. (15-30mi here)
I wear a half-mask respirator with organic vapor canisters and N95 dust filters on it. It takes out 99% of smell and taste of the smoke. I'm not working around nasty stuff much now, so my OV cans last for years. I'll get new ones before they see solvents much.
It was bad again today in Grass Pants, too, with PM2.5 in the air at 153. The two fires west of us are Taylor Creek (Acres 52,839, 95% contained) and Klondike (Acres 98,358, 40% contained.) They expect to let them burn until the October rains put them out. Thanks, Tree Huggers, for letting the fuel build up for 50 years...
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On 8/25/2018 11:10 AM, snipped-for-privacy@whidbey.com wrote: > I have had to relieve the diameter of tap shanks many times in order > to tap deep holes or to cross a bore and the like. This morning I > needed to reduce the shank of a 5/16-18 tap. The job required that all > but about 3/8" of the shank diameter needed to be turned down. This > meant that in order to do the turning in one chucking the end of the > tap needed to be supported. The tap in question was a spiral point > tap. So I used a live center for support. I put a .25 thick piece of > aluminum between the point of the center and the tap. Then, with the > spindle turning, I cranked the tailstock quill forward until the > center and the tap points had both made pretty deep depressions in the > aluminum piece. I used a coated threading insert to turn down the tap. > 255 RPM and .004" feed. The material was removed in one pass. I > plunged the tool into the work where the cut would not be an > interrupted cut. Then fed away from the chuck by hand to remove the > incomplete threads. This part of the cutting was an interrupted cut so > I wanted to feel the cutting. After removing the incomplete threads > the cut was reversed so that the tool was feeding towards the chuck. > The operation worked quite well and the threading insert still looks > good. HSS taps are hard but coated carbide is much harder. > Eric >
I had to turn down the shank on a reamer not to long ago, and wrote about it here I think. Used a bright shiny solid carbide TNMG insert. The cut screamed, but the finished looked really good. I thought about using a similar coated insert, but I didn't have one at the time. A coated one might not have been "quite" as sharp though so who knows how it would work out. Now, thanks to your post... I might try a coated one next time around.
Nice to have some metal working content. Thank you.
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One of my second-hand adjustable reamers lacks an adjusting nut so when I finally needed that size I had to make one. The thread is 9/16-18 but a standard nut was way too loose. I was able to thread the new nut to a close fit from a 1/2" Grade 8 nut with a hand-ground HSS internal threading bit that stayed sharp at least long enough to make the part, twice, the first time 9/16-20.
Grade 8 hardware has worked well for me when I need to make a high strength or long wearing part using custom HSS forming tools such as radius cutters. -jsw
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On Tuesday, August 28, 2018 at 9:50:30 PM UTC-4, Jim Wilkins wrote:

Grade 8 bolts are medium-carbon, with a tensile strength around 150 kips and core hardness in the mid-30s Rc. That's within the range for good HSS cutters, although cutting-edge life won't be great.
--
Ed Huntress

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