Welcome to FAB Math!

There are many math-related questions that come up in the process of Fab Academy.

14. Mils, mm, and fractional Inches - Mental Math for PCB production

American system is crazy and difficult for non-Americans to jump into. Most Americans also don't know about "Mils", 1/1000 of an inch. All will benefit from quick conversions and a general intutive sense for approximation in this context.

Let's use the following approximations:

• 1 inch =~ 25 mm
• 1/1024 inch =~ 1 mil

together this means:

• 1 mm =~ 40 mils

seems convenient to bypass inches altogether and have a direct mm to mils conversion

Some examples:

• 0.4 mm (tip) =~ 16 mil (multiply by 40)
• 1/32 inch =~ 32 mil (use powers of 2)

13. CNC Feedrate and Chipload Equations

Consider the equation: Feed rate = chipload x flute number x RPM

• Feed rate is linear speed of the spindle
• Chipload is the size of the chip that the bit creates
• Flute number is the number of flutes on the bit
• RPM is the rotational speed of the spindle

In the above equation, there are 3 independent variables, and 1 dependent variable.

i.e. we can theoretically set the feed rate, flute number, and RPM. Chipload will depend on that choice.

Therefore it makes sense to write the equation to highlight this:

Chipload = Feed rate / (flute number x RPM)

From this equation we can easily understand what factors we might change if the chipload is not ideal.

12. Mathematics of the Dogbone

Source