Introducing the first of many design series posts by those at Porter Machine Works aimed at showcasing the expertise behind the development, industrial design and engineering of every piece of equipment purchased.
The theme of this post is tolerances, and why they rule the industry.
Perfect Parts Don’t Exist
Due to the variation caused by material characteristics and manufacturing processes, parts are never made to perfect specifications. They will always be made slightly larger or slightly smaller than their nominal design. The variation is captured in design as tolerances; the range of variation acceptable in the design.
Tolerances and Cost
The cost and performance of PMW rings is directly related to the tolerance analysis completed during the design stages. The tighter, smaller the tolerance the more difficult a part is to produce. And the firearms industry values the small numbers.
It is quite acceptable to find the standard use of 0.025mm (0.001”) on machined parts in the industry. What you’re looking at there is about a quarter of the thickness of a human hair.
A number of considerations are made when designing parts for manufacture. Many come down to the products requiring a tight and reliable fit to surfaces from varying manufacturers, of different materials and different coatings.
Let’s look at the cross section dimensions of the picatinny rail.
The NATO standard has three contact surfaces. These can range from 18.95mm to 19.05mm in width and 4.17mm to 3.92mm in height with any value falling within these ranges deemed acceptable.
One of the first questions is how to ensure that the rings fit correctly to the range of rails available to shooters everywhere. Up for consideration are the levels in quality available on the market as well as the different coatings that might be added; Cerakote can add 0.02mm to the overall thickness of a part.
See below an example. The same set of Porter Machine Works rings on rails with a different finishes; Cerakote (left) and anodising (right). The first clearly shows the gap on the ring’s clamp slot (despite Cerakote finish adding to the final dimensions of a finished part) where the second, anodised rail has minimal gap.
Prototyping is our friend, and to make sure that the Porter Machine Works rings are always the best foundation for your optic setup, each extreme case is considered and explored during the prototyping stages. Coupled with adopting the best industry standards and practices in design and machining, you the shooter can be certain that a set of rings from Porter Machine Works will be the best platform for whatever kit you’re running, for whatever purpose.