Occasionally we get calls from people who have some salvaged lumber and they want make their own flooring. Here are a few details to consider.
The fit of the tong and groove is critical if the wood floor is going to perform well. A loose fit can lead to squeaks while a fit that is too tight will make the floor hard to install. If you put two short straight boards together and then hold them in the air by one of them the other should not fall off. A quick shake should cause the boards to disengage. A difference of a few thousandths of an inch can make a significant difference.
Almost all wood flooring is made with the top face slightly wider than the bottom. As the floor is installed the top touches first leaving a slight gap between the boards on the bottom. The difference in width between the top and bottom avoids cracks showing between the boards in areas of slight sub floor irregularity.
A groove on the top inside corner of the tong allows a space for the nail heads as an addition aid to a tight fitting floor.
Some individuals with good skill levels have been able to produce serviceable flooring from antique wood, but most high quality reclaimed flooring is made by experienced craftspeople.