this post was submitted on 26 Aug 2023
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The linguistics of metrology is not exactly a topic I'm particularly passionate about, but if yiu look at the technical definition of accuracy, it essentially is the same as a tolerance.
Accuracy: the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard.
And when it comes to decimal places, you'd never display more than you really need. If a dimension is +/- .010" there is absolutely no reason to display it to 4 decimal places. That doesn't win you anything. More importantly, I'm sure a company like Tesla doesn't even use drawings at all. I'm sure they are paperless and send out their models for machining.
I think there is a very important distinction between accuracy and tolerance in engineering. +/- .010" is not a dimension, but a tolerance that can be applied to a dimension. However if your example was changed to a .010" dimension, I would agree with you as I stated in my last comment. There is no need to give any further accuracy to that dimension if you are just adding zeros to the end (unless you are using block tolerances that rely on a specific number of digits to correspond with a standard tolerance). Unfortunately, not everything is designed using the same units and you will inevitably end up with a part designed in mm that uses a bolt-on component using a hole span in inches (for example, a nice round 1-in span). If you want a +/-1 mm tolerance on that part, you wouldn't want to round every dimension to the nearest mm because you may end up with a tolerance of 24-26 mm when you really wanted 24.4 to 26.4 mm. I like to provide true dimensional accuracy (to microns or .0001" if I'm not just adding zeros) and then apply a suitable tolerance independently, using GD&T.
Regarding paperless manufacturing, I agree that many components are made straight from the models these days and imported directly into a CNC machine. However, there should always be a drawing or a digital equivalent a drawing. This is the contract that specifies acceptable tolerances to the manufacturer, and it will be used during QA inspection to determine if an acceptable part has been delivered.
I think there is an important distinction between accuracy and precision in engineering. I'm having flashbacks of sitting in class when the professor was going over this stuff. I honestly always found it some of the most boring topics in the curriculum.
One of my physics profs had a story about this. He needed two resistors to be very similar in performance for a circuit he was making, so he asked for a couple of the super-high-quality ones.
His advisor said "fuck that, get the 1% bin, they'll be bimodal at 1% above and below rating, sort em and find two that match to the degree you need"
That's kind of analogous; do you need to try to hit a particular value (accuracy) or do you need things in a consistent relation to one another (precision)?