Neanderpundit

Equipment exists to get very accurate and very careful measurements of just about anything you can imagine. Small shops tend to use hand tools, such as micrometers and calipers; time was, a master machinist might not have his car keys or his wallet in his pocket, but he’d damned sure have a Micrometer. When I bought Dad his own 6″ dial caliper in 73, he felt as if he’d Arrived; he made a leather shoulder holster for it and it never (Literally) left his side.

medium sized shops or shops doing extremely high precision machining will often use a device called a CMM or Coordinate Measuring Machine. For almost everything, the CMM is the last word in measurement, because it uses scales and math to calculate diameter, depth, concentricity, all of the things you need to know about a manufactured part.

CMM’s are not cheap. A good one will set you back a hundred K, and the unfortunate reality is, a cheap CMM is not a good cmm. You could end up with a measuring machine whose resolution is less than your machining center, and the information you get from it is worse than useless.

For large shops, there is usually a combination of small handheld tools and CMM’s. Large production shops also use what are called “Hard gauges” to bridge the gap between calipers and micrometers (Which take some skill to read) and CMM’s which are costly and usually not used directly on the shop floor (Though this is changing).

A Hard gauge is a way for a relatively unskilled person to test if a parts dimensions are in tolerance without having to know too much about the process, or think too much about the gauging. A hard gauge can be as simple as a “Go/Nogo” gauge, used to check the size of a hole. This type of gauge has one pin at the stated size of the hole, and another pin at just slightly beyond the maximum limit of the hole size. They look like this.

It’s pretty simple to use. If the ‘Go” doesn’t go in, it’s too small. If the “No go” goes in, it’s too big. Cletiii everywhere can use them like masters.

Another type of hard gauge that is very common is the Flush Pin gauge. This is an interesting type of gauge that is based on the ability of people to feel things they cannot see.

Take a hair. A blonde one, if you can get it. Lay it flat on a piece of glass. Now rub your finger over it. If you don’t have serious nerve damage in your hands, you can easily feel it. The hair is about four thousandths of an inch thick. Most people can feel about a half a thou. That’s .0005.

A Flush Pin gauge is often used to check the chamfer of a hole. it involves a hollow cylinder with a ground pin captive inside it. On the bottom is a flat ground surface on the cylinder and a cone on the pin. The gauge is used by putting the cylinder on the surface and pushing the pin down into the chamfer. The top of the gauge has a “Step” surface in the cylinder while the pin is ground flat.

This is what one looks like. You can see the “step” on the top (left, in this photo)

The magic to this little gauge is that the step all0ows you to tell, just by using your finger, if the chamfer has been cut to the correct depth, and do so within .0005. You check to make sure that the pin sticks up above the first step, which you can easily do just by sliding your finger across it, and below the second step, likewise. And those two steps can be as small as .0005 apart, and most people can still feel it easily. If you have very sensitive fingers, you can feel .0001.

This type of gauge can be used to check the depth of a hole, the length of a shoulder, and many other critical dimensions, with remarkable accuracy, very quickly, by a moron.

IN large production operations, rather than tie up an expensive machine like a CMM checking every part, most parts are checked with hard gauges, (Or, in automated systems, the electronic equivalent of hard gauges) and only representative samples are tested in the CMM.

The CMM is used for another reason as well: as the tools in a machine wear, they get microscopically smaller. This changes the part by very small amounts, too small to be caught by the hard gauges, but they will be significant in time. When the parts are checked in the CMM, offset data is passed on to the machines that cut the parts, so the machines stay well within tolerance until the tools life has expired, and in time, the process will be monitored so closely that the tools can be changed predictively, knowing exactly how many cuts each one has before it will wear excessively or fail.

In automated systems and in some manual systems, electronic hard gauges are used so that the data can be passed directly to the machines, and in very critically dimensioned parts, this is an important part of the modern manufacturing process.

I remember setting up a cell on the northside in the winter of 1998 that had to meet 2.00 CPK requirements at a nearly impossible bore tolerance. We were doing OK, and halfway through the runoff some idiot opened the garage door ten feet away from the cell, and it stuck open.

We figured we were fucked. As the machines cooled from room temp (around 69) to a nice 38 degrees, the coefficient of thermal expansion of the iron made the lathes make smaller and smaller parts, but the hard gauges sent offset data back to the machne, and we made 2.00 CPK like falling off a log. THe gauges corrected for the machine’s thermal shrinkage as it happened, each part was machined a bit smaller but the offset made a bit bigger, and despite miserable conditions we got the job done.

The company who made that part is long gone, but the process is still around, and the parts still being made, having been sold to another company as a unit in the company’s closing auction.

Another type of gauge that is common across the industry is the air gauge. In operation, it’s extremely simple. A bore- say a bearing bore- is to be tested to a specific diameter.
Now, you can use mechanical bore gauges or calipers, but two cletii will have two different “Feels”. One will tighten an ID mike until it barely touches, then read it, and another will tighten it as if it wewre a clamp, and read it. These two cletii will produce dramatically different readings for the same part, quite literally.

Anyway, back to the bore. An air gauge consists usually of a plug that is almost the size of the bore, with several holes of a specific size bored into the edge. Air is plumbed to these holes, and when the plug is put into the bore, the holes are partially occluded. The air pressure goes up. An air column gauge shows the rise in pressure as LED’s on a column. Those gauges look like this:

There are many types of air gauge but the ones in common usage are green when the part is in spec, yellow when they approach upper or lower tolerance, and red when they’re out of tolerance. The air can only leave the holes at the velocity allowed by the gap between the plug and the bore; a tight bore lets less air through, and the pressure rises, a loose bore lets more air through, and the pressure drops. No “Feel” is necesary. No talent is required. Cletiii over the world use these to measure the most stringent tolerances, because most of them can more or less drive, and they understand the whole distinction between “Green, yellow, and red”

The other thing Air gauging does is to let you measure things that can be measured in almost no other way. Springfield Armory, years back, made ‘Star Gauged” barrels, which were and are very highly sought after. The manufacturing of that gauge was difficult and it was easily damaged. Air gauges do the job so much more efficiently and are incredibly easy (By comparison) to manufacture.

Modern rifle barrels are made by any number of methods, and each method has it’s hardcore adherents. Compared to the manufacturing methods of even 100 years ago, the way mfrs put those twists into the barrels today is- if not better, at least more reliable. No matter what firearm you choose to shoot, no matter how the rifling is made, the liklihood that the barrel will shoot far more effectively than your ability to point it at anything is great- because of the way they’re measured and how that measurement is used.

has come a long way. When Parsons and Sikorsky decided to numerically control machines that made punches for helicopter rotor parts, they quickly realized that they didn’t know a lot about computers. MIT took the project in hand and made the first NC machines out of old Cincinnati mills. At the time, it literally was Numerical control; the circuitry took numeric instructions and made the servomotors move. Not until several years later did they actually integrate memory into the machines making them true Computer Numerical controls.

Without the CNC machine, a powerful lot of stuff the military needed could not be made, and so in concert with MIT, the Military purchased and retrofitted some machines and provided them to some of the shops they used, so they could get the stuff they needed.

The AR grew up in this time. NC and later CNC machining made the AR platform not only possible but fairly easy to build- it did for firearms what Henry Ford did to cars. It was no longer necesary to be a competent gunsmith or even machinist to make a good functioning firearm, pretty much any cletus could put a forging into a machine and a serviceable part would come out.

This was also sort of true of other firearms, like the AK, which, while it was not the child of CNC certainly benefitted by it and still does. The difference is the AK is designed to have wide open tolerances which allowed it to operate under many conditions, and withstand almost unbelievable abuse; the tradeoff is marginal accuracy, and pretty much always will be.

Unlike the AK, the AR was designed to be a precision firearm with precision fitted components, but with the ability for tolerance stack and human error removed.

Remember the post about Tolerance Stack? The brilliant thing about a CNC machine is that once a part has been verified, and tested exclusively, it can be duplicated with precise and repeatable accuracy almost infinitely. A properly cared for machine tool with appropriate tooling and careful operation has an indeterminate life; there really isn’t any way of telling how long one will last. Many of my customers are still using equipment made by Pratt Whitney and Giddings and Lewis that are now fifty or more years old. The leadscrews have automatic lubrication, they ways and gibs adjust readily and easily, and as long as they are not abused they continue to make good parts.

Stoner knew this, and he designed the components of his firearms to be easy to make with high precision. Let’s look at one of the most critical parts- though a lot of AR owners don’t even know it’s there.

You can click on the image to embiggenate.

This is the barrel adapter. Most people never see it as a separate part of their barrel, but if you look up into your receiver you should be able to see the threads that join it to the barrel inside the adapter.

This little bastard is brilliant. I mean, bloody brilliant.

In a bolt action rifle, or in other types of autos, the receiver is a solid machined piece that has the barrel screwed or pinned or sweated into the receiver face. This in itself requires a good deal of hand fitting, but the additional issue of fitting the bolt in place, making sure the bolt hits the recever lugs in the right place, and doesn’t allow excess headspace, is a good damned deal of work for even a talented gunsmith.

This little chunk of steel makes all that go away. You see, in a CNC machine, when you cut a thread, the thread always begins and ends in the same place, every single time, always. Which means that when you CNC machine a barrel, it’s threads will always start at, say, nine o’clock, and end at eleven o’clock. The threads in the barrel adapter are similarly oriented.

When the barrel adapter is made, it is machined in two operations, on a CNC machine. First, the face is squared, giving you surface A. Then the material is bored out of the center, the bottom of the hole faced, (Surface C)and the threads are cut. Then the outside of the part is machined, giving you diameter D and surface B. The part is then cut off and the secondary operations are performed. This means several things.
1: The surfaces A, B, and C are always parallel to one another, to the limit of the machine’s accuracy.
2: The surfaces A, B, and C are perpendicular to the diameter D.
3: Diameter D is concentric with the root diameter of the thread T
4: The thickness between surface A and B and the distance between surface A and surface C is predictable, repeatable, and consistent from one part to another.

Far better than can ever be done by hand in multiple operations, and far better than the average gunsmith wants to do. When JMB, God rest his soul, designed the M2 Garand (thanks Tam), he made it so the hand fitting was easy and simple. When Stoner made the M16, he made it so no hand fitting was required, period.

The upshot of this is subtle but vital. Barrels are made in a bunch of different ways, but at the end, the last thing that happens is that they get threaded and chambered. Because of CNC manufacture, threading the barrel into the barrel adapter means that the headspace is part of the barrel and adapter, and the headspace does not depend on the receiver but moves entire as a unit from receiver to receiver. Thus, a barrel/bolt that is a good accurate combination at a specific headspace can be moved from one firearm to another and the accuracy of the barrel moves with the barrel, assuming it is placed in a properly manufactured firearm. Here’s the subtle bit: No hand fitting is required to get the relationship between the barrel and the barrel adapter just right, because it’s done in CNC machines, and if done to spec it will always be just right. Sure, it’s possible to get a match grade barrel that’s headspaced as tight as a drum, but even then, you’ll see that they are sold as sets. You get the barrel, the adapter, and the bolt. Therein lies the accuracy of the firearm, and nothing else can effect it like those components can.

Professor Hale links to a story where a lesbian woman makes a fuss over being refused communion.

You have to read the whole story to understand what is going on. Jewelled Cranberry has an excellent post on it here. I suggest you read the whole thing.

Money quote, from the “offended” party:

“You brought your politics, not your God into that Church yesterday, and you will pay dearly on the day of judgment for judging me,” she wrote in a letter to Guarnizo. “I will pray for your soul, but first I will do everything in my power to see that you are removed from parish life so that you will not be permitted to harm any more families.”

Harming families? By following the laws of the Church? How can this be?

It is “harming Families” because it isn’t “Tolerant”.

Sorry. The only person who brought their politics into the church was the lesbian woman, and this is the kind of axe you will see them swinging over and over again as the government forces the Church to act according to it’s PC wishes, and not the rules set down by the Creator.

Still think that Gays ought to be free to marry? Really, they’re the kindest, gentlest people you know, right?

So long as you’re not a devout priest trying to stay firm to the Calling. Then watch out.

Look, I think people should just be as happy as they can get themselves. If they can only be happy at the expense of other’s faith, that’s a sort of a dealbreaker. You can think that Gays seeking the recognition of marriage is solely and only about their love for one another.

But you’re wrong.

This is but one example. There are others, and this situation will recur and recur until the Church, beaten and bruised, will slink off to a corner and all but die, it’s only adherents being those too stubborn to be pushed around by an intrusive PC government.

God forbid, on the other hand, that you raise a question about the new State Sponsored religion of Ecological awareness and Planet Saving Nonsense, then you’re a criminal. That is a church to which I will never belong, preferring my soul to my freedom, thankyouverymuch. Don’t expect me to give up either without a hard won fight.

To the church leaders who rolled belly up and submitted to this woman: Shame on you. I would be embarrassed to call myself a Catholic, but for the fact that you now cannot. Oh, you can pretend, but you’re in the soup now. I hope you like it.