tap 1/2" in steel



It's not the thread that's stronger, it's ultimately the bolt that is stronger. The deeper NC thread cut makes the bolt snap easier...
I assume it would apply differently to an inside thread, but the inserted / threaded rod / tool / bolt would have to be considered as well.
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More cross-sectional area left in the bolt (larger root diameter).
Except in extreme cases of material strength mis-match (like steel bolt in plastic hole/nut) the limiting factor with proper thread engagement (~1 diameter, IIRC, but I may not RC) is the core of the bolt, not the threads.
It's a factoid I recall from one of my practical machine shop courses, but a quick look into the bolt reference guide someone mentioned here a while ago confirms it (10-24 and 10-32 are both listed with failure torques in theaded holes of various thickness, and the 10-32 numbers are consistently higher).
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CLIP
Well said.
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says...

The really instructive case is for 6-32 vs 6-40
Jim
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As usual the answer depends.... NF has a larger minor diameter so the bolt is stronger..............provided that the thread engagement is long enough that the threads don't strip out. At least that is what I think. I ought to go back and do some more reading on Bolts.
Dan
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I think it depends on the material. Fine threads in soft metal are not as strong as coarse threads.
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You seem to have confused "chasing" a thread on a lathe with cutting a thread on a lathe. Two different processes. The former is indeed a high-skill and largely out of date (e.g., for old Germans, Swiss, Norwegians, and Americans). The latter is a basic, not very difficult skill to master in Lathework 101. In cutting a lathe thread on a lathe you must have a screw-cutting capability -- that means, a lead screw and appropriate gearing -- whether a built-in "quick change" gear box or separate gears that you have to change for each pitch. Alternatively, a lathe with some kind of CNC control for cutting threads. The key is that the tool is a single-point cutting tool. "Chasing" a thread is an altogether different (and largely obsolete) skill. In chasing, you use a multi-point tool. Sort of looks like a lathe tool with saw teeth on the end. The spacing of the teeth determines the pitch of the screw. You place the chasing tool against the work while the work is turning, at the same time moving the tool toward the headstock. If you do it just right, you'll find yourself cutting a screw thread. That's a shallow, starting thread. Then you have to push the tool in successively farther until you get the thread depth you want. Since it takes several passes, you have to "chase" the thread with the tool to line it up for the next cut. With luck, you should be able to get a decent thread after a few hundred tries. Now for an inside thread (eg., a nut) you do the same, only this time you can't really see the thread you're trying to cut ..a few years and a few thousand attempts should bring it home. Any one who is serious about machining should try (and succeed in) chasing an external thread at least once in his life -- makes you appreciate tools like taps and dies. As much as possible I do all my threading and tapping on lathe -- using taps and dies. For tapping you use a spring-mounted point tool to hold the tap against the work with the right pressure. Assures a perfect allignment almost always. For threading, I made up similar, sprint-loaded, die holders. Over the years, I've accumulated a very big assortment of weird taps and dies but every once in a while, especially when helping a friend restore an antique instrument, you come across threads that follow no recognizable standard. Then you have to do it on the lathe. For threading, it isn't much of a hassle. But if you have to tap a weird thread in a small hole and can't just fake it by using a heli-coil, then it is worth making your own tap. Not that big a deal. Although I have a bunch of very big taps and dies (up to 1.5 x 8) I usually start by cutting big threads on the lathe, and then finish them off and clean up using the tap or die as appropriate. It's a lot easier doing it that way than getting a die lined up correctly .. Also a lot less brute force needed. I doubt if there's more than a dozen denizens of this news group who can consistently chase decent threads -- I'm not one of them. As for threading on a lathe without using taps and dies, I'd guess that its a basic skill mastered by more than 95% of this NG.
Boris
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"Boris Beizer" snipped-for-privacy@sprintmail.com
wrt chasing a thread

It may have been easier in wrought iron. I can't see even trying it on modern steel. The method does survive for turning wood threads. I have a few of the old hand tools, but have not had the urge to press them against substance yet. Frank Morrison
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the
few
them
You have a point there. I urged people to try this technique just for the experience, but... My first attempt was on a 3/8 aluminum rod. After butchering a foot or two of this material, I switched to 1/4" brass. Never did try steel. Obviously, you do this at the slowest speed, using the back gear. I once saw a 90 year old something watchmaker who could zip out watch screws about as fast as it would take using a die .. note, mostly left-handed threads. This makes we wonder if the prevalence of left-hand threads in Germany and Switzerland hs to do with the fact that it much easier to chase a left-hand thread on a screw than a right-hand thread.
Boris
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a
two
about
left-hand
Chasing survived in the US late into the last century, by hobbyists involved in optics. The special, large-diameter, fine-pitch threads used in making telescopes are all but impossible to make any other way on a home-shop lathe. And you probably will wind up taking your outside-threading chaser and bending the end over to make your internal threading tool. It can be hard to get the pitch exactly right on two different tools, although the real experts seem to do it Ok.
Several old guys who were members of an astromony club nearby were experts at it. My uncle, who taught shop in the school in that town and who knew all those old guys, picked it up and became quite good at it himself. He taught me, and I was able to chase good threads after relatively few tries. A key to it is to have a very smooth top surface on your follow rest (which looks like the follow rest on a woodworking lathe, except that it clamps onto your compound). I polished mine and stoned the burrs off with an Arkansas stone.
Since I never picked up much interest in making telescopes, I lost the skill over the years. But it's really not as difficult as it sounds. While you're learning, you do tend to make double-start threads at twice the pitch you intended <g>, but you get past that.
BTW, most of those optical-equipment threads were cut in brass, but I've done it in steel with no problem.
Ed Huntress
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Tap is preferable if you have a suitable tap on hand. Lathe works when you don't, and perhaps one isn't even available.
Smallest hole that can be single-point threaded on a lathe depends on the machinist, the material and the threaded depth. I know I've threaded holes about 1/4" dia, and I think I've done smaller. Made the cutting tools by grinding them from broken drillbits. I have one boring bar with a 1/16" shank.
On Sat, 6 Nov 2004 14:27:15 -0800, "Walter Harley"

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Another great sourc for tapping small holes is broken taps. The cutting point is all done for you and the angles are perfect. Just grind away all the interfearing other points.
Karl
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"Walter Harley" snipped-for-privacy@cafewalterNOSPAM.com

As another suggests, you can combine the two and use a tap pushed by the tailstock of a lathe. This will give a concentric thread, which will be harder to produce hand tapping in the vise. If your tap has a small 60 deg hole centered on the back end, you can fit a dead center into that (with the tap held in a tap wrench as well) to aid hand turning, and alternate torquing the ts handwheel and tap wrench ( always renewing and keeping pressure from the dead center on the tap) as you go. This can also be done under power, jogging the motor so you tap just a bit at a time. Sometimes you may want to single point some or most of the thread first (cut it with a boring bar in the lathe), then finish with a hand tap. Even if done in the vise, the tap will then follow the started single-point cut, so remain concentric to the bore.
The smallest internal thread you can do on the lathe is the same as the smallest internal thread you can do with a tap--multi point vs single point is the only difference. For me it's about 3/4 10. Frank Morrison
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LOL. Me thinks the man doth protesteth too much!
:^)
Jim
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On Sat, 6 Nov 2004 14:27:15 -0800, "Walter Harley"

Certainly!
Hmmm... Yes, no, and maybe! I have a 1/2-20 tap.... that is what I'd use in the lathe.
If I had a bunch of these to do, I'd BUY a tap....
But if I only had one to do and had no tap, I would consider chasing the thread in the lathe.

There really isn't one too small, though grinding the tool might become prohibitive for very small (common) threads (just buy a tap and get it over with)..... as Larry the Cable Guy would say, "Get 'er done."
IMHO, the decision on how to accomplish this task would be built around these questions:
-how many holes do I need to thread? -do I have the tooling, now? -how much will tooling cost? -how long will it take to get the tooling? -how quickly do I have to get this done?
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