I received a question about the frog needing to be in place when flattening a plane.
And my answer is there are lots of fairy tails out there. If someone wants to sound knowledgeable, they throw in the frog needs to be attached. My question is do you really think you can move a cast iron plane body into registration with 2 (12-24 ) screws and a screw driver?
In industry, the piece to be machined is set up so that the largest surface can be machined In its free state. This establishes the parts datum surface. And a datum is a plain, line, surface, or feature assumed to be perfect.The rest of the diffination deals with tolerancing. Dimensions comes from a datum but in itself a datum has no tolerance.The last part paraphrased
Once the largest surface is machined ( bottom of the plane body) then one has control of all plains of motion, of which there are twelve, and the sides and then the frog seats can be machined by locating on the bottom. Not the other way around.
If there is a problem with the bottom not being flat then is is because of the person who took the milling marks out when finishing the job, Which would not effect the relation of the planes bottom and the planes seats. Or casting stress being relieved over a 100 years. And the seating area being the thickest eare would be least effected.
The idea probably came from a person who wanted to sound knowledgeable and to embellish an article to sell a book or magazine. And it continues to get parretted.
The world is not flat even though every one knew that it was at one time so my questions remains. Do you really think you can move a cast iron plane body into registration with 2 (12-24 ) screws and a screw driver?