Z-table > change pulley calculation


Z-table > change pulley calculation

Postby bloq » Fri Mar 20, 2015 7:58 am


i am not an engineer so please apologize the question: I was wondering how i can change the pulleys which are used for the z lift table. Currently there is a 48 tooth and a 20 tooth pulley connected with a 101 mxl belt. Am i right that this is a ratio of 2.4? What if i took a 15 inch pulley and a 36 inch pulley. This would also be 2.4. Does this change anything besides the center distance? What happens if i use another belt (like 100). Would this change anything in the system which i should take into consideration? I know there is something like teeth in mesh but i have no idea what that means.

thank you!

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Re: Z-table > change pulley calculation

Postby Zebethyal » Fri Mar 20, 2015 9:59 am

Hi There,

You can potentially use any pulleys and belts you like, it does not even really matter what the ratio is - originally this laser was designed with 1:1 ratio on the Z axis, the reduction gearing was added at a later stage.

All you really care about is how many steps on the Z axis drive equate to 1mm or 1" or some other repeatable value of movement on the Z axis itself and this can be calculated up front by multiplying it out, or worked out after the fact by measurement and fine tuning.

Josef Prusa has a good article on this on his website that is self proving and used for 3D printer extruder calibration by measurement, however the principle is the same for the Z axis and this method does not need to know what the actual screw pitch, gear train etc, that is in use.

For working it out in advance you need to know what type of stepper you are using (how many degrees per step), what level of micro stepping you are using, the screw pitch and the gear ratio.

For my Z axis with 20 and 48 tooth pulleys, 1.8 degree steppers, 1/16 microstepping and M6x1 threaded rod the calculation would be as follows:

For the motor
1.8 degrees/step = (360/1.8) 200 steps per revolution
1/16 microsteps = (200*16) 3200 microsteps per revolution

For a 1:1 gearing with 1mm pitch screw
microsteps / screw pitch = (3200/1) 3200 microsteps per mm

Gear ratio
20 tooth driver, 48 tooth driven = (48/20) 2.4

with step down gearbox = (3200*2.4) 7680 microsteps per revolution of driven gear

which with a 1mm pitch = (7680/1) 7680 steps per mm
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