Mach3 Setting Steps Per Unit

Mach3 CNC Control software, CNC tutorials.


How to set the Steps Per Unit in Mach3.

In order to achieve accurate cuts on your 3 axis cnc router table, you must set the steps per unit accurately. Figuring out how far your motor has to turn to move a specific distance can be done the old fashioned way using calculations or the easy way, using Mach3.



In case you are the stubborn type who likes to do things the old school way here are the formulas you need to complete to figure out your steps per unit for your stepper motors.

First you must calculate the mechanical drive of your system. In other words you need to know how to calculate the number of revolutions of the motor shaft (Motor Revs per Unit) to move the axis by one unit.

You will also need to know the the raw pitch of your leadscrew (the distance from thread crest to thread crest) as well as the number of thread starts. Inch screws may be specified by threads per inch (TPI). The pitch is 1/TPI. Example :(the pitch of an 8 TPI single start screw is 1/8 = 0.125″. 

The effective screw pitch  is the distance the axis moves in one revolution of the screw.

screw revolutions per unit (SRPU) SRPU= 1/effective screw pitch

motor revs per unit (MRPU)  MRPU=SRPU*Ns/Nm

Ns= number of teeth on Screw

Nm=number of teeth on the pinion

example: 8tpi screw connected to  the motor with a toothed belt  with 48 tooth pulley onthe screw and a 16 tooth pinion the motor shaft pitch would be 8×48/16=24.

shaft revs per unit = 1/(tooth pitch *Ns)

motor revs per unit = shaft revs per unit* Ns/Nm

Motor steps per revolution 200 step per revolution 1.8 degrees per step. Stepper motors

mach3 steps per unit = mach3 steps per rev * motor revs per unit

As you can see there are a lot of things to factor in. I don’t plan to prove these calculations but you can feel free to.

Take the Easy Way Out

If you don’t feel like spending the rest of the afternoon figuring equations then I suggest you watch this video instead. It will walk you step by step through the process.

You will need:

A yard stick

Two Quick Clamps

Dial Indicator 

Indicator base

The basic process involves clamping a yard stick to the rails of your router table. Go into Mach3 and use the Set Steps Per Unit button to do the calculations for you. This process only takes a few minutes and will improve the quality of your work instantly. If you would like a set of plans for the Warp Drive Project CLICK HERE.






12 Responses to “Mach3 Setting Steps Per Unit”

  • […] is a link to the written instruction for the tutorial. Mach3 Setting Steps Per Unit – THE MAKERS GUIDE Bill __________________ Making the world a better place, one project at a time. CNC Router, […]

  • Electron Exciter on July 15, 2013

    Excellent calibration tutorial. Found it via a Joe’s CNC link just wanted to let ya know yer video was helpful!

    • Bill Griggs on July 19, 2013

      Thanks for letting me know. If you have an idea on something you would like to see, let me know.

  • […] the tutorials I have in the works. Here is a link to the written instruction for the tutorial. Mach3 Setting Steps Per Unit – THE MAKERS GUIDE Bill googletag.cmd.push(function() { googletag.display('div-gpt-ad-1389628723172-0'); }); […]

  • Brian Tracy on February 24, 2015

    Nice video. I was wondering how to use Mach3 to have the stepper motors rotate a single revolution from the gcode. For example, if i put in a number like 1, it interprets that number to be 1 inch. Though i want one revolution from the stepper motors (360 degrees) from my gcode script. I know the motors have 200 steps, 1.8 deg per step with no microstepping but Mach3 is calibrated to translate a certain distance and not an angle. How can I back calculate this to an exact angle?
    Thank you.

    • Bill Griggs on February 27, 2015


      Mach supports up to 6 axis gcode. Axis X,Y & Z are linear. Axis A,B & C can be linear or Angular. Hook your stepper to one of these 3 axis and set it to angular.

  • […] This video and blog post should help you. Mach3 Setting Steps Per Unit – THE MAKERS GUIDE Bill __________________ Making the world a better place, one project at a time. CNC Router, […]

  • habibmgh on August 5, 2016

    hi bill what about mk3 from planet-cnc with thier 6A 250 stepper controller

    • Bill Griggs on September 27, 2016

      I don’t understand your question. Please be more specific.

    • Bill Griggs on September 27, 2016

      What about it?

  • Doug Berrow on June 6, 2017

    Mr. Griggs hi. My name is Doug and I have always routed by hand. I am retired and make plaques for family/veterans. I just bought a (fireball x90) from a guy who has run the machine for 4 years on mach3 demo. He ran the roadrunner for me just once and that’s it. I am new at this. I can jog the cnc over my work piece and have tried to run the roadrunner without cutting but it stopped half way. I think I’m missing a step or 2. Frustrated…can someone email me how to get to cutting already. If I had some instruction to read and get to cutting just once, I learn a lot better. Please can anyone help…thanks.


    • Bill Griggs on June 10, 2017

      The fact that the program stops 1/2 way through is probably because the demo only executes the first 500 lines of code. A full version would not have this limitation.

      If you need to get a licensed copy of Mach 3 you can do it at I would be glad to help you get started.


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