How to configure the screw pitch in mach3

[Eric C Stoltzfus]

I am working on setting up the software for my diy CNC machine. I am using Mach3 but I can't figure out how to configure the screw pitch. I have two different types of screws. On the Y and Z axis I have 1/2-10 5 start screws. On the X axis I have a 1/2-10 single start screw. How do I enter this into Mach3?

[Bill George]

Never did screw pitches in Mach3, but you might research over at CNCZone.

[Chuck Saunders]

I don't think that is defined. You define the number of pulses to move one inch in the axis you are defining. That way the entire drivetrain is taken into account and Mach3 pulses the motor enough to get the desired travel.
Chuck

[Gary Campbell]

Your 1/2-10 5 start should be 2 turns per inch or 0.5" advancement per revolution. Your 1/2-10 should be 10 turns per inch or .1 advancement per inch.

Take the number of pulse per rev from the driver setting (200,400,800,1600,2000, etc) and multiply it by the turns per inch to get your steps per inch (unit) number.

[Steve Peterson]

Most stepper motors have 200 full steps per revolution. The stepper controller often uses "partial" micro steps to increase resolution. My controller uses 10 microsteps, so it ends up with 2000 steps per revolution. A 1/2-10 single start screw would need to rotate 10 times to travel one inch, so it would use 20000 steps per inch. The 1/2-10 5 start screws only need to rotate 2 times to travel an inch, so they would use 4000 steps per inch.

Your controller might have a different number of micro steps. 8 or 16 micro steps are probably fairly common. Also some ball screws have a metric pitch with one rotation per 0.5cm. This is close to 5 rotations per inch, specifically 5.08 rotations per inch. My 10 microstep controller would use 2000 steps per revolution times 5.08 rotations per inch for a total of 10160 steps per inch.

Another solution with less math would be to just start with a value around 10000 and measure how far the head moves when you give it a command to move a certain distance. Adjust the value up or down until a 10" move command equals 10" of travel. If you have imperial screws, then the number should be a round number like 4000, 5000, or 10000, and not something like 7428.

Steve