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:
Two Quick Clamps
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.