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Machine Shop and Tool Talk

Taps and Dies Purpose?


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Old 09-09-2017, 02:30:33 AM
maxdub maxdub is offline
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Question Taps and Dies Purpose?

So you know how there is thread chasers, regular tap and dies, round dies for cutting new threads. some people say don't use hex die to make a new thread they are only for restoring old or damaged ones, i thought that that was thread chasers job and round cutting dies is for a new thread. so what is the regular tap and die for. the hex kind.

I know that some hex dies are also for cutting new threads just like the round ones they have a split through them.
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Old 09-09-2017, 08:00:15 AM
Rob Charles Rob Charles is offline
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Default Re: Taps and Dies PURPOSE!?!?

I have found that some of the "Hex" repair dies cut the threads smaller than std sometimes a lot . That is probably ok for large threads but not so much on smaller. You can cut a new thread with the Hexes but they likely tear as they cut the full thread or you need to turn you stock smaller then usual.I think the Hex type of dies are marketed more to the mechanics trade for repair work rather than new work. When I use a die I would grab a split round dies first. If I don't have that type then I would go with a solid rd. die. My last choice is a hex repair die. Rob
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Old 09-09-2017, 01:24:28 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Taps and Dies Purpose?

I have used both, hex and Round, on metals up to 1/2". I also have used many dies up to 8" for pipe. Some round, a few hex (up to 2"), and a few sectional (for 6 & 8 inch) For the small stuff, I have had equal results with both the round and hex, although the hex seemed to work a little better on brass and bronze. As long as the taps and dies were new or in good condition, no issues. The trick is to keep them cool and 'lubricated' with a good cutting oil. NOTE - cutting oil is NOT a lubricant!. Using a tap or die that is worn or has chipped teeth is a no-no, and of course will give poor results. For certain metals like Stainless steel or the copper type alloys, a good sharp cutting tool is needed for best results as well. Different metals use different coolants as well. Using vegtable cutting oil on stainless steel will give you fits, as an example.

As for pipe dies and taps - my grandfather gave me a hex set made by an outfit named Robins. It ranged from 1/8" up to 2" and had 2 stocks. One for the small pipe, with a 1 foot handle, and one for larger (1" and up) that had a 30" handle. The heads of both stocks were the same, which made for a hard job, working on the 1/8 and 1/4 inch pipe, due to the stock weight. They did an excellent job though - leaving exact and clean threads, no matter what the size pipe. I also have a set of Rigid pipe dies. When new they work OK, but after about 20 cuts, the replaceable dies wear and then start to tear up the pipe. They especially don't like the Chinese crap they call pipe now days - chipping and dulling in as few as 5 or 6 threads. if you cut crap material, you get crappy results. The sectional dies I used were driven with a 'pony' It was a large machine that had a reduction drive. If you let the dies get too hot, or if the dies jammed, the entire machine would flip both the machine and the pipe vice in an instant. They were dangerous to use. On one Job I was on, the 8" head had hit an imbedded 1/4" ball bearing that was included within the steel in the pipe (made in Korea). The sectional die jammed and the machine flipped a 10 foot long section of pipe nearly straight up before it hit the cement ceiling. The cast iron motors' gear housing then exploded into fragments. Then the pipe fell to the ground, breaking a mans arm. like I said - dangerous. The die was also broken in two, and the pipe crushed where it dug in against the ball bearing.

After all that, when we were done installing the pipe, we found that it would not hold a test - there was a hidden seam in the pipe that leaked. The leak was found by accident - while testing the fitting joints for leaks (test failed overnight), One of the guys dropped a bottle of testing soap, and it landed on another section of pipe. We were surprised to see a mound of bubbles in the middle of a section of pipe! We eventually found that over 30 sections of pipe failed - 2 months work NFG!

Tips for using taps and dies - take your time. 'The hurrier you go, the behinder you get' certainly applies when cutting threads. Flush with cutting oil and or coolant, and keep dies and or tap cool at all times. Clear out chips and spurles before they jam into the work. DO NOT use bare fingers for cleaning - you can do serious damage. Nothing like getting cutting oil into a fresh cut . If cutting threads onto rod, make sure the OD of the rod is appropiate. You can't cut a 3/8 thread on a 1/2' rod, after all! Make sure you use the tap or die that is proper for the job. There are running, tapered and bottoming taps, and tapered and running dies as well.

Thread chasers are another story. They are meant to 'repair' threads that are already present, but are damaged. They cannot make their own new threads, and if are used to do so, usually will tear up the work or will break. They are meant to straighten or slightly cut damaged threads. If you run a regular die over damaged threads, you take a chance that the die will actually cut new threads over the old, instead of following those already there. Use the proper tool for the job at hand. thread chasers will not work if the work is bent (like a bolt), or the work is hardened.
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Old 09-19-2017, 09:49:35 AM
Sbcasenut Sbcasenut is offline
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Default Re: Taps and Dies Purpose?

Being young and a bit short on money to get a Rigid hand threader and all the dies, I took a different route when it came to pipe threads. I have taps up to 1/2 NPT and dies up to 1/4 NPT. Past that, I figured it was a waste of time to cut threads with a die and no proper threading handle.

But I still needed male pipe threads on many occasions, so this summer I finally got the taper attachment on my South Bend 13 lathe working. I had to make a clamp to hold it, since the original was gone, and I still have lots to learn about cutting pipe threads, but 1/2 NPT threaded real nice. Another plus is I use HSS hand ground threading tools on my lathes, and I can sharpen my threading tool whenever it gets dull.

No sense having a lathe if it can't be as versatile as you are!
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Old 09-19-2017, 10:25:28 AM
Pete Spaco Pete Spaco is offline
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Default Re: Taps and Dies Purpose?

Is it absolutely correct then, that ALL hex dies are for rethreading/repair only?

I haven't bought any threading dies lately, but I don't remember the little cards upon which the dies are sold, telling me when a die is for rethreading vs cutting new threads.

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Old 09-19-2017, 02:01:19 PM
Glenn Gieszler Glenn Gieszler is offline
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Default Re: Taps and Dies Purpose?

Not to my knowledge, they could be ordered in different types of threads as shown here, that is probably where the rub lies as a v thread and whitworth are likely to have a different root diameter

I do have several square dies stamped with an R. Which I assume could mean repair they likely came from great northern railroad but don't know as I haven't had the chance to use them
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Old 09-19-2017, 03:15:46 PM
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Motormowers Motormowers is offline
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Default Re: Taps and Dies Purpose?

I've worked with so called " mechanics " that you would swear think a tap was meant to be broken off whatever they screw it in. lol
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Old 09-19-2017, 03:53:59 PM
Rob Charles Rob Charles is offline
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Default Re: Taps and Dies Purpose?

The "R" on your die is likely for Briggs std "R" which is a RH pipe thread . I believe there's also and "L" for left hand. Rob
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Old 09-19-2017, 09:12:11 PM
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Elden DuRand Elden DuRand is offline
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Default Re: Taps and Dies Purpose?

I've got a Vermont-American (1965 or so American) tap and die set. The dies are all hex and non-adjustable and cut threads that fit well with commercial nuts.
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Old 09-19-2017, 10:55:15 PM
akuna akuna is offline
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Default Re: Taps and Dies Purpose?

Well there is no easy answer. They make split round dies, hex standard size, hex nut size, and solid round dies for threading. Seems like they make standard nut size hex re-threading dies as well as odd size hex re-threading dies. Possible they make round ones, have no idea for sure.
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Old 09-20-2017, 06:06:32 PM
tdmidget tdmidget is offline
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Default Re: Taps and Dies Purpose?

Any tap or die should cut the thread to spec. There is a lot of junk out there. Run from "sets" as fast as you can unless just using them to clean rust and goo out of threads. You can get what you pay for but no more. A decent 1/4-20 spiral point tap will set you back close to $15. You can see that buying a set of stuff you may never need and may never work right anyway is false economy. Buy quality tools as you need them. You will save in the long run. After using junk straight flute taps from the cheapo sets you will think you have died and gone to heaven .
As for "chasers" , pure hokum. A tap acts as it's own lead screw. Anything it removes was in the wrong place and should have been removed. Using damaged or malformed threads is a quick path to galling and further damage. Always clean threads before reuse. In the power generation industry we have fasteners quite commonly to 6 inches holding steam at 3500 psi. At every disassembly they are cleaned and inspected, replaced as needed. When in doubt we run a tap or die as the case may be to insure proper thread form.
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Old 09-26-2017, 04:00:41 PM
BillWojo BillWojo is offline
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Default Re: Taps and Dies Purpose?

^^^^ What tdmidget said. Did you used to hang out at Practical Machinist? I am MrBridgeport over there. Haven't stopped by there in ages.
Anyway, only buy quality taps, the stuff a real machine shop uses. Yes, they are expensive but cheap in the long run. Look at flea markets for stuff and stay away from the old stuff. The newer generation of cutting tools is a vast improvement over what came before. Look for spiral point and spiral plug taps.
By the way, on the side of a tap you will see a GH number. Number 3 will cut a standard size thread, Number 4 or larger is used if the part is going to be plated and each increase in number size cuts the thread oversized by 0.0005. That's why if you tap a part with a GH7 tap, the fastener will seem loose.

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