CNC Machining, QA/QC, And the World of Good Enough

[williejc]

Colt's TDP is intellectual property allowing them to mass produce AR platform rifles and carbines to meet agreed upon specs. Colt claims that their product can not be reverse engineered. The TDP also addresses parts manufacturing, of course. The TDP is all about mass production.

I'm not qualified to say much except that I have been studying AR technical topics and agree with Eurodriver, who pointed out that attention to detail in assembly is essential.

[MegademiC]

Fair enough, parts that are in spec should always work. I'm just not comfortable that all assemblers ensure that.


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That is exactly what sets companies apart. Both parts and methods of assembly have a specification. If you adhere to those, you will never have a problem.

[sinister]

There will be no problem with bin parts if those parts are made to spec. The AR really is a marvel of modern engineering and was far ahead of its time when it was developed. It's the first design to control headspacing to the point all bolts are a drop in fit with all barrel assemblies, a leap forward in rifle manufacturing. It's the first issue rifle to fully embrace modern production methods and it was readily adaptable to manufacturing control methods yet to be developed. That's it's real edge over the M14, AK, FAL and other designs

Yes and no.

There have been millions of AKs made in dozens of countries -- lots of potential for variation. The FN FAL was adopted and manufactured world-wide in non-Com-bloc states. Barring Metric-Standard conflict major components are supposed to swap.

In a perfect world components will be interchangeable. In practice, not so much.

Parts built to spec are inter-changeable. An M16 made in Canada, Singapore, the Philippines, or Korea works with parts made in Connecticut or South Carolina.

[noonesshowmonkey]

Parts built to spec are inter-changeable. An M16 made in Canada, Singapore, the Philippines, or Korea works with parts made in Connecticut or South Carolina.

This is, overwhelmingly, my experience.

So, to my original question: what are we buying but a few lumps of aluminium that have been CNC machined to nearly identical specifications, and produced at levels of precision far beyond the operating tolerances of the rifle itself?

I'll agree that when buying a complete rifle, or even sub-assemblies like (especially, due to it carrying the barrel) an upper receiver or a lower, buying from a company that has rigorous QA/QC combined with well paid, knowledgeable technicians is worth the money.

I buy materials and features, not brands. Sabatier turns out a beautiful knife. I don't buy them due to their brand name, I buy them because they are the combination of materials, features, process, form and function.

In the case of the AR-15, especially as we stick close to 'mil-spec', the vanilla M4/M16/AR-15, most of (if not all) of the above variables are held as constants. We have a clear pattern, a clear specification, that determines what the product is. If parts are being produced within specification, which with the state of CNC machining these days is essentially a given, they (should) be functionally identical but for branding. The assembly of those parts may vary significantly from one shop to another.

Outside of other features, such as a fully ambidextrous lower, or lighteneing, or 'enhanced' BCGs, or any of the many other tinkereings with the AR pattern, the specifications are known to function when used in total.

This concept seems to bear fruit in conventional wisdom: do we not know to invest in the barrel, the trigger, and the optic? Those places with the largest functional variability?

[williejc]

There seems to be a wide choice of barrels. What are the criteria? About chrome plating, does it make a lesser quality barrel a better barrel? How much more cost does the plating process add?

[sinister]

It's like everything else talked about -- what was the quality of the barrel before plating? How was plating applied? How thick was it applied? Was it treated afterward to avoid hydrogen embrittlement?

Send a shit barrel to an aerospace plater and you get a shit barrel with a space-age coating. Send a hand-cut barrel to a bumper plater and you get a gnat's ass-tube that peels and cracks.

As we've pointed out before, the drawings and materials lists state what the customer wants. The mil-spec states what minimum inspection and function-test criteria an item must pass.

If a commercial source doesn't do batch or sample tests they should have a good return policy.

[MegademiC]

This is, overwhelmingly, my experience.

So, to my original question: what are we buying but a few lumps of aluminium that have been CNC machined to nearly identical specifications, and produced at levels of precision far beyond the operating tolerances of the rifle itself?

I'll agree that when buying a complete rifle, or even sub-assemblies like (especially, due to it carrying the barrel) an upper receiver or a lower, buying from a company that has rigorous QA/QC combined with well paid, knowledgeable technicians is worth the money.

I buy materials and features, not brands. Sabatier turns out a beautiful knife. I don't buy them due to their brand name, I buy them because they are the combination of materials, features, process, form and function.

In the case of the AR-15, especially as we stick close to 'mil-spec', the vanilla M4/M16/AR-15, most of (if not all) of the above variables are held as constants. We have a clear pattern, a clear specification, that determines what the product is. If parts are being produced within specification, which with the state of CNC machining these days is essentially a given, they (should) be functionally identical but for branding. The assembly of those parts may vary significantly from one shop to another.

Outside of other features, such as a fully ambidextrous lower, or lighteneing, or 'enhanced' BCGs, or any of the many other tinkereings with the AR pattern, the specifications are known to function when used in total.

This concept seems to bear fruit in conventional wisdom: do we not know to invest in the barrel, the trigger, and the optic? Those places with the largest functional variability?

You are assuming what is going into the cnc is perfect, and that the cnc is perfect, and that nothing happens to it between manufacturing the part and reaching the customer. None of those are true, and all offer an opportunity to deviate from the spec.

[Zirk208]

If it was all as simple as inputting the data into a CNC machine, and trusting the technology, there wouldn't be a need for offset buffer retainers.

As seen here: https://www.m4carbine.net/showthread...al-buffer-wear

[PrevailFI]

All other things being equal, assembly is the most important part of manufacturing. Period.

You can take a bunch of engine parts, kit them up so that they are identical in quality and config, and I'll guarantee you that a guy who builds engines professionally will get better results than a shade tree mech with a chiltons manual.

Most people who argue the "better than" or "just as good" angle have very little manufacturing knowledge, or they would understand this.

That's not to say that "vendor a" can't make a rifle the equal of "vendor b". But skilled, experienced labor costs more, and if you introduce non value-added steps like NDT and QA into the process, it drives the cost up. That's just a fact.


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Correct assembly of an AR from decent quality parts is ludicrously easy. Armorers are no longer arcane figures, spoken of with awe and reverence. Mechanically inclined 16 year olds build solid ARs by watching Brownell's videos.


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[JC5188]

Correct assembly of an AR from decent quality parts is ludicrously easy. Armorers are no longer arcane figures, spoken of with awe and reverence. Mechanically inclined 16 year olds build solid ARs by watching Brownell's videos.


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So then how do guns get out in the wild with sub-standard staking, etc?


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