The Photo Chemical Machining Institute (PCMI.org) is the global trade association for the companies that produce photo etched precision metal components. In its standard verbiage, it states that minimum dimensional tolerances can be as tight as +/- 10% of metal thickness.
That's somewhat true, but they don't explain what consequences that choice can entail. A while back, we did a study to illustrate the impact of sheet sizes and tolerances on photo etching costs. The study results are here.
The study clearly demonstrates that sheet sizes, and thus total labor, have a substantial impact on economy. Every sheet, regardless of size, has to be handled in and out of the same seven steps on every job.
We made the example for a 1-inch part in .010" stainless steel. On 12 x 12 sheets, it would take 15 sheets to make 5000 parts. On 18 x 24 sheets, 5000 pieces would take only 5 sheets.
The other important cost factor is inspection time. At +/- 10% tolerances, there is an increased probability that lots will not pass AQL 2.5, our standard. Generally, we consider a "sub lot" to be one sheet subject to AQL 2.5.
Lots that do not pass AQL, are required to undergo 100% dimensional inspection.
Even though we have 3 automated optical inspection systems, the through-rate is about 400 pieces/hour. That would add about 1.25 hours of inspection for every thousand pieces.
Our standard practice is to quote on the basis of +/-15% of metal thickness, which easily supports +/-.005" for metals up to .030" thick.
In addition and at your request, we are happy to quote based on a +/-.010% tolerance. This lets you evaluate whether the added cost of tighter tolerances creates a greater benefit to your application.
We are happy to give you alternative quotes so you can see the impact on cost for tighter tolerances.