20 or 16 Tooth Pulleys for international version

Hi All,

I’m planning to build this machine in the EU and will be sourcing most parts locally. The current kit and parts list mention 16 tooth pulleys, but the Marlin Blog entry mentions:

This is for 16th stepping, 20 Tooth Pulleys and 8mm 1.25 threaded rod.

Which should I get for the international version? 20 or 16 tooth and will it make any difference in precision? I’d like the machine to be as precise as possible.


The IE edition refers to the tubing diameter and has nothing to do with the pulley teeth count. The only difference is the pulley diameter, the belt teeth pitch is still 2mm. So a 20mm pulley will give you 25% more linear movement per rotation than the 16mm pulley but 25% less torque. I am using 20mm ones but don’t think it really matters that much. I think that the machine rigidity will swamp out the theoretical linear resolution, (just guessing not measured).

You do need to make sure that the firmware you compile and download has the correct number of teeth represented in the configuration.h file. The #define DEFAULT_AXIS_STEPS_PER_UNIT will depend on your pulley teeth, belt pitch, stepper microsteps/step, and stepper steps/rotation.

Something like:
(mm/tooth)(tooth/rotation)(rotation/steps)(steps/microsteps) = mm/microstep

I get (1/160)(mm/microstep) for my 32 microstep/step 20 tooth setup. That is 0.00625 mm/microstep. Do you think that is enough resolution?

For example my configuration.h file has this line:
//SLC for 20teeth/mm puley, 2mm G2 belt, 200 step/rot, 32 microsteps/step
#define DEFAULT_AXIS_STEPS_PER_UNIT {160,160,4535.44,760*1.1}

The first number is for X, and second for Y. The third number is for the Z-axis and is for my imperial threaded rod. You will change that if you use an 8mm rod. The fourth is only used if you make it into a 3D printer with an extruder.

BTW - I would go with 32microsteps if your driver supports it. I think the steppers run smoother and sound better.

Awesome reply, Thank you!

I am not very good at explaining things well. At first all the info was in 3 different sites and doing updates was a pain. I have been trying to move all the info to this site but now the site is getting a little confusing. Guess I need to work on it this week.

Ah thx SteveC! So I need to combine the 16 or 20 tooth 32 step with the 8MM international Z-axis. I will go for the 16 tooth for now. If I find it to slow and perfer speed over tork I can always swap.

Thx for the quick reply!

So I’ve now build a machine with 16 Tooth pulleys and a 8mm rod, which I would like to 32nd stepping. Does anyone have a configuration file for that? I tried comparing the configuration.h between the Marlin_16_32_090615 and Marlin_20_16th_8mm but I failed to find what I need to alter…

Edit: I cried to soon. I found the http://www.prusaprinters.org/calculator/ page. If I have a 8mm rod a 1.8degree and 32nd stepping it gives me 5120.

So the line from Marlin_16_32_090615:
#define DEFAULT_AXIS_STEPS_PER_UNIT {200,200,4535.44,200} // default steps per unit for Ultimaker

should change to:
#define DEFAULT_AXIS_STEPS_PER_UNIT {200,200,5120.44,200} // default steps per unit for Ultimaker

Can somebody confirm?

Yes, 5120, take off the .44

Oh yes thanks, the point is a decimal separator… Not used to that.