Thread mic, or wires?

As soon as Styrofoam became common for packaging (remember the days of cardboard packaging?) I've kept a piece or two in my box to hold thread wires. Yeah, I've dug several out of the chip pan, but that was before Styrofoam.
 
Thread wires are a pain but they're cheap and get the job done. For home use I'd recommend this.

Thread mic saves a lot of time but comes with added expense. Probably best for job shop work where you have lots of threads to measure, but time is money.

Finally for production, thread ring gauges are best. They only give a Go No-Go for one size, but they're fast and very reliable.
 
Been using triangles for many years. I have the type mentioned above but also the type that actually attach to the mic anvils. They're pretty expensive compared to what I paid!
 
Thread mikes win hands down, the ones that I have, I bought on e bay relatively cheaply, they have fixed anvils, and are in the more common pitch ranges; I also bought Polish made interchangeable anvil sets up to 4" but sold them along with my business; thread mikes are fast, accurate, and read directly in pitch diameter, no calculations necessary, just look up the thread specs in Machinery's Handbook --- and go at it. Having said that, I agree with most of the other comments, you most always just fit a thread to a nut; one thing, 'tho, best to run a sharp tap through the nut first to eliminate possible burrs. About the only time I bother to use a thread mike is when I'm making a thread (plug) gage to use for gaging a internal thread to be cut in some pitch or diameter that I do not have a sample to use as a gage.
I also have triangles and wires, but hardly ever use either. One old machinist that I knew once brought a job to me to do, with wires to gage the thread, they were all that he had to do the job, made of baling wire! They worked well enough ---
 
For me- full profile lay down threading inserts with a thread mic make it a lot easier to hit class 3a threads when single point threading.
 
No doubt thread mics win but for 30-50$ you can do all threads no matter type or pitch. Kind of a staple for a machinist I think.
 
The main advantage for me to use wires with my current projects are the ability to measure the PD and other aspects to greater accuracy. Thread mic typically have three decimal place readings. Although generally good for hardware, I needed four decimal place readings to produce ISO:1948-1987 camera lens threads.

The Pratt and Whitney Supermicrometer G-2100 makes it very easy to read the correct dimensions for PD due to the pressure sensor on the tail stock. Hand micrometers are more accessible if the part is checked during the machining process (on a lathe). The G-2100 micrometer is great for measuring multiple components from various suppliers.
 
This is an update to a post I made a while back using a single wire as opposed to three wires to measure external screw threads. Some may ask why use one wire? It is a hell of a lot easier to manipulate one wire as opposed to three wires and not as expensive as a thread mike.

Please disregard this if you are building interplanetary spaceships, artificial hearts, bionic eyeballs or fusion reactors. It has been hypothesized that 90% of all fasteners are in the 2A fit category and the above mentioned project builders will not be happy with anything other than a 3A fit. One other thing if you make an external thread to 3A tolerance and mate it to a 2B internal thread it is not a class 3 fit.

Ok, we got that out of the way. In the previous post I was asked about the issues using a single wire method and I stated that you needed a sample to start with or a predetermined PD with tolerances and I wasn’t confident of the accuracy but it works well enough to make tractor and steam shovel parts.

So it got me to thinking is there a way to determine the PD of any diameter external thread and measure it fairly accurate with only one wire? This resulted in writing a program for my calculator to determine the measurement of the PD over one wire.



Here’s where the rubber meets the road. In some attempts to thread I was disappointed to find I had to undersize the measurement to have the mating internal thread fit nicely. So I went back and looked at the formula and determined that the formula to calculate the PD from Machinery’s Handbook calculated close to the max PD allowed. If you throw in a few more variables that are not perfect your fit might come out snug.

So back to the formula and I tweaked it so that the PD was about in the middle of a 2A tolerance and the results now were much more predictable.



This brings up the final point, if you want to hit the PD accurately your thread tool needs to be as accurate as possible, the tool needs to be perpendicular to the work and last but not least the wire needs to be very accurate in being round and sized, both within the required diameter for the pitch and diameter measurement. A small error in diameter of the wire results in a larger error in the PD.

Most of what I thread I have a corresponding internal thread to check against so I don’t worry too much about the accuracy as I’m not building any of the aforementioned items. I also don’t have the luxury of having thread wires so I have used small drills, copper wire, and paper clips anything close to working to measure the PD. Plus I don’t have a T&C grinder to make my threading tools and use inserts, my HSS tools are hand ground on iffy pedestal grinders.



If I pay close attention to my cutting tools and my setup and use the proper wire I feel confident I can hit the PD of any external thread and it will fit even if I don’t have the mating internal thread, without juggling three wires and losing one in the chip pan.
 
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