According to the technical literature at https://qtcgears.com/tools/catalogs/PDF_Q420/Tech.pdf
, there are 4 measures referred to as "backlash" on a spur cylindrical gear.
None of them has the numerical value indicated in the combined FreeCAD view. Except when it is "zero".
I tested 3 gear combinations and with one of the gears I chose the backlash value, in the combined view, of 0.010 mm (10 microns).
All gears were made with 16 teeth, and modules of 1, 5 and 10 mm.
I measured the gaps directly on the gears, on the circumference of the primitive diameter. For that I cut the gears in the primitive diameter.
The gear on the left had the backlash changed, the gear on the right was designed with the backlash equal to "zero".
Apparently, the backlash value obtained on the changed gear is equal to; J (real) = J (inf.) X m x Z / 4, this by gear.
J (real) = Backlash measured in gear
J (inf) = Baclash reported in combined view
m = gear module
Z = number of teeth
Therefore, in case you need a specific backlash value, the following function should be used:
J (inf) = J (real) / (m x Z / 4)
This is a resource that I am using to meet my needs and produce the backlash that interests me. I don't know if it is the most correct way to proceed.
Note: I did the same test with 20 teeth gears, to define how the number of teeth influenced the final backlash value.