Let's say during a side milling operation, a 40mm dia tool is used, so an offset is specified using a syntax as follows:
G41 D4
From what I understand from the above syntax is that, D must be followed by a number obtained by dividing the tool dia by 10. Am I right? I've seen another example where a 25mm dia tool was used and the D there was followed by 2 and not 2.5 (25 divided by 10). How come?
Can you please explain how the number that must be followed by "D" must be obtained.
First of all you should consider there are many different dialects of G-code, you should always mentioned the specifications of the machine you are working with.
The G41 as mentioned here in LinuxCNC page, indicates the tool. When the value starts with a D it refers to the tool number not the diameter. So D4 refers to the tool number 4 and D2 refers to tool number 2. Also
if there is no D word the radius of the currently loaded tool will be used
so I think if you want to indicate the radius of the currently loaded tool you should put
G41 20
or
G41 12.5