Oh ACME, how must we love thee? Let us count the ways.....

Most lathes have two, :rimshot: some worn by mere turning.
Others endure endless trips of carriage pushing chips whilst cutting internal threads.
Pssh-shaw! Maybe OK in a captive shop, job shops have to compete.

Our own Dr.Al [discipline of practice unknown] posted an outstanding means he built for tap & die management with storage and instant retrievibility, retrievebility, retrieveability Bite me, spell check That bought out my compliments for all of the design, completion, and presentation.
:popcorn:
Which then cascaded into a lengthy but accurate hack of his thread, naturally. As a confessed thread-hacker (often about threading oddly enough) seemed expedient to r-u-n-n o-f-t and post that content independently.

Therefore, herewith and with out further delay.........[*]

There are ACME taps with a double cut arrangement, presents roughing portion ahead including a long tapered lead section, due proportional mass of material removal creating a full thread, so concept not completely foreign. That length and waist make smaller ones feel fragile, multiplied by higher cost.

BTW, when facing any quantity of internal ACME threads, here is a lathe trick. Single point the pitch and thread profile anywhere from 10%-80% less than full, then run the tap. If evaluating fit, a sample 3 diameters long will be reliable substitute for an actual ($$!!) gauge. The actual trick now, having run the single point before hand, is sync'ed to shave least possible remaining material for actual finish.

Works on V-threads too, especially when expecting to finish with a big ol' coarse tap and 3' wrench...

Our practice modified this a bit farther, making bronze nuts for lead screws. New taps went by way of toolroom first, mounted between centers on cutter grinder to remove a bit of the OD, depending on size, ~ +/-less than 15%. Now a roughing tool, saved untold hours repeatedly poking a bar in there for chips following the lathe's lead screw. The logic reduced ensuing wear of machine overall, concentrated on half nut and screw.

Of all things personal computing had promised, (yes microsoft, apple, print cartridge designers, I-phone, android....Bite me again, you too spell check many of those failed to materialize; such as reducing consumption of trees for paper, streamlining administration, or being that great equalizer of sought information and random knowledge.
[*] One was never promoted that reigns supreme......all hail copy/ paste :bow:

On a roll now, itching to drop something at https://www.homemadetools.net/forum/...ght-lies-42152 as well!

One of the things I have always tried to do whether making internal threads on ACME, Butrus, Jacobs, API tapered, NC, NF, UNC, UNF UNEF, UNS, ETC, you get the picture is if I don't have a tap for the size and pitch, I will make the male thread first, hopefully out of a grade of material I can harden after processing. once I have the go no go thread made I grove it just like a tap and grind a cutting relief on the first couple of threads, in effect making a tap. If I already own the tap of the size in question then I do as you described, single pointing the thread to between 60 and 80% sometimes as much as 95% depending on the material being threaded IE stainless 4140 , stress proof, 4330,ETC, For bronze or cast iron maybe only 60% even when finishing off with the go no go tap gage
When making metric threads without a tap on either of my lathes since I do not have metric change over gears I try to get as near to 0% error pitch as possible then run a hardened bolt in and out a few times to finish off the thread almost any metric thread length less than 2xdia seems to work just fine long external metric threads are another thing entirely. but 1 of my lates has enough thread combinations to go from 4 TPI 228 TPI starting at 4 TPI advancing by 1/4 threads per inch through 5 TPI then by 1/2through 12 TPI from then on to 27 TPI in increments of 1 thread per inch eventually advancing by 2 threads and on to much larger increments. like 40 56 64 72 80 120 there are a few numbers in there I have probably left out so most of the more common metric threads from 1 to 2.5 mm I can come close

Agreed Frank S; threads present challenges that can be overcome. I don't mind spinning up a fresh plug gauge, marking and storing it logically. Then, a bit of anti-rust and they won't stale....ever.
I can't imagine working environment where those practices aren't utilized; catalogs get whipped out, awaiting arrival of lab grade gauge. Granted there are specifications/ tolerances that is necessary. In normal conditions, guys wonder why they can't manipulate thread wires anymore, interpolate unmatched pitches, shave minor diameter corrections....

The other day my neighbor brought me a bolt and asked, do you have this size metric bolt on hand.
I put my calipers on it then a pitch gage and said no and no one else will have one either, because it is not metric a metric bolt would have something like 8.8 or 10.3 bossed on the head not 6 bars. That is a grade 8 5/8 12 TPI bolt it measures out to be just under .620" dia at the threads given that the threads are worn a little that would be consistent with a 5/8" bolt a metric would be 16 mm or .629-.003" looks feels and measures real close to the same dia but as far as I know there is on 16mm bolt with a 2.117 mm pitch.
As it turned out it was in fact a 5/8-12 UN bolt. I figure it was proprietary spec. by the manufacture in an attempt to make you buy replacements only from them

Quote:

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Originally Posted by Frank S

The other day my neighbor brought me a bolt and asked, do you have this size metric bolt......... As it turned out it was in fact a 5/8-12 UN bolt. I figure it was proprietary spec. by the manufacture in an attempt to make you buy replacements only from them

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The new math, where 12 can be odd!

Regarding proprietary threads; a few come about through practice of 'design for manufacturing'. A lot of measuring tools have this, they sought a certain degree of thread engagement [or movement per revolution] not offered in standards like NC or NF. Included here, the continued use of old drawings and equipment. The replacement part was seen as a side benefit; being that historically the era's products outlast anything offered later.

Quote:

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Originally Posted by Toolmaker51

The new math, where 12 can be odd!

Regarding proprietary threads; a few come about through practice of 'design for manufacturing'. A lot of measuring tools have this, they sought a certain degree of thread engagement [or movement per revolution] not offered in standards like NC or NF. Included here, the continued use of old drawings and equipment. The replacement part was seen as a side benefit; being that historically the era's products outlast anything offered later.

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I have spent the better part of 3 years now on a project that I have redesigned tested found areas which could be improved by making a few changes while said changes often created other issues which had to be addressed. As much as I prefer to use off the shelf items in an assembly whenever possible there are times when nothing of a standard stock item exists in the size or shape, I require. Or if it does the level of quality is so sadly lacking or the cost is prohibitive, unless I import it. I don't have a problem with using imported stuff from most countries around the world as long as their products meet my standards.
I would actually prefer to use all metric materials if that were even possible. But just try and purchase sheet and formed structural materials in steel or aluminum in this country at any kind of reasonable price let alone considering availability. Si if I cannot use metric everywhere I chose to use metric nowhere the exception being bearings as those have been metric standard for decades around the world, bearings in imperial inch dimensions are the difficult to find things.
I have 4 requirements I insist on in my design criteria #1 strength and durability #2 Ease of manufacture from a production standpoint #3 aesthetically pleasing for marketability #4 cost of manufacture. However, this particular project does carry a 5th requirement the least amount of weight reasonably possible. My partner the bean counter would re arrange these priorities if I would let him