At Vista Industrial Products, we always fabricate to print. If a part cannot be fabricated to print, we note deviations during the quote process and list them as exceptions and or conditions on the quote letter. This means we can fabricate to print with some approval of these exceptions; otherwise, we will no bid. These exceptions are also known as deviations after approval. We review prints thoroughly by confirming all materials are available. This includes material types, hardware and finishes to keep things simple. This is basic information has to be defined to allow for any company to quote.
A common mistake is calling out the correct material type. For a Formed Aluminum Sheet Metal Part, an example of this mistake is calling 6061-T6 as the material type. This material will always crack and some engineers do not know this. We would by default deviate from this material and provide the following exception.
“Quoting this part using Al 5052-H32.”
Finish is black powder. Usually, we would need a manufacturer and part number of the black powder. Our preferred powder is Cardinal Finishing Industries. We would ask the customer to pick a finish from their website.
The next image is a machining tolerance block commonly used on sheet metal parts. Machine, Sheet Metal and Weldment parts all require different tolerance requirements. Sadly, this mistake is too common and engineers always default to machining tolerances. See VIPs Default Sheet Metal Tolerancing.
Tighter tolerances is correlated to pricing. The tighter the tolerance; the more costly the part becomes. Because sheet metal is naturally flexible, majority of parts that are formed are toleranced based on the restrained condition.
The exception VIP would state as a note under the part number is the following.
“Quoted using VIP’s Standard Sheet Metal Tolerances.”
So what is the difference from a deviation and exception? For the most part, they are basically the same and just differ based on the industry.