# Built my own Cnc mill and need help to calc steps per mm



## Wesley Bramer (Jul 19, 2016)

Trying to figure out my steps per mm Using the Rep Rap Calculator

Here is the link to the NEMA 23 Steppers that i bought as a kit with the cnc controller.

3-Axis-3A-Stepper-Controller-Cnc-Kit-Nema23-24V-Psu-For-Milling-Machine 152$ cad

Here is the link to the leadscrew i have selected

t8 800 mm leadscew with 2mm pitch and 8mm dia
22$ cad


From the above sites i was able to determine my:

Motor Step Angle 1.8
Leadscrew Pitch 2mm

I have the dip switches on my cnc board set to be at 1/8 micro step.

The part that i think im messing up is the pitch preset where i am only guessing that is m8 1.25 mm per rotation.

With the above information i get 800 steps per mm which seems absurd
PLEASE SOMEONE HELP ME if i roatate the rod 1 full revolution it travels 8.1mm

Am i just messing up the calculation???


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## Stick486 (Jan 4, 2013)

welcome to the forums Wesley...


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## gjackson52 (Jul 4, 2015)

Welcome to the Forum !


Gary


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## MEBCWD (Jan 14, 2012)

If your measurements are correct then I calculate each step of the stepper motor to be 0.0405mm so for 1mm you would have 24.6913 steps.

Is this what you are looking for?


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## Garyk (Dec 29, 2011)

Welcome aboard. To much math for my old brain so I guess there is no CNC in my future.


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## SteveMI (May 29, 2011)

Steppers that are 1.8 degree per step result in 360 degrees / 1.8 = 200 steps per revolution. Nothing metric or imperial involved.

My CNC is based on a German design and the distance traveled in tuning the steppers seemed wrong to me. It had 0.47" diameter lead screw which led me to consider it was metric, so I Googled and found there is a metric version of ACME called Trapezoidal which is offered in 12 mm (0.472") and a thread pitch of 3 mm which comes to 8.46 pitch (TPI) in Imperial. Imperial Acme uses the "pitch" in inches, while Metric Tapezoidal uses the "pitch" in mm. 

So, taking that;

TPI * steps = steps per TPI units 

8.46 * 200 = 1,692 steps per inch. With Gecko micro-stepping (10 x) it became 16,920 and agreed with Mach3 distance traveled.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

For your metric with T8 1.5 pitch (my chart only shows 1.5 pitch fine thread for T8). Every revolution of the T8 is 1.5 mm in distance, so 1 mm / 1.5 mm = .66 mm to use in calculation for travel.

Turns per mm travel * steps = steps per millimeter
.66 * 200 = 132 steps per millimeter 

Then multiply the steps per millimeter by the micro-stepping.

132 * 8 = 1,056 steps per millimeter

If the lead screw is a non-standard 2 pitch, then 1 / 2 = .50 and;
.50 * 200 = 100 steps per millimeter
100 * 8 = 800 steps per millimeter

Remember you are using a fine thread lead screw!

Also, remember only 3 countries remain non-metric and this response is from a citizen of one of those.

Steve.


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## honesttjohn (Feb 17, 2015)

Guess that's why I got my CNC already assembled, tuned, and ready to go.

See, Gary. There's a way!!!

HJ


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## SteveMI (May 29, 2011)

honesttjohn said:


> Guess that's why I got my CNC already assembled, tuned, and ready to go.


You are a wise man John.

Steve.


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## honesttjohn (Feb 17, 2015)

SteveMI said:


> You are a wise man John.
> 
> Steve.



Not quite. I just know that I have enough frustrations trying to get mine to follow directions, let alone do the settings. 

I am talking about my CNC ..........

HJ


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