# Machsupport Forum

## Mach Discussion => General Mach Discussion => Topic started by: cncman on April 25, 2018, 11:56:01 AM

Title: Problem to setup a belt driven 4th axis
Post by: cncman on April 25, 2018, 11:56:01 AM
Hi guys!
How can i setup my belt driven 4th axis with ratio 4:1 ?
Thanks for any help!
Vasili
Title: Re: Problem to setup a belt driven 4th axis
Post by: Davek0974 on April 26, 2018, 02:09:07 AM
Simple - use pulleys with that ratio of teeth?

20 on one, 80 on the other etc :)
Title: Re: Problem to setup a belt driven 4th axis
Post by: cncman on April 26, 2018, 04:12:18 AM
Yes i know that but how will i tune it in Motor tune? This is what i don't get.
Title: Re: Problem to setup a belt driven 4th axis
Post by: Tweakie.CNC on April 26, 2018, 04:28:43 AM
Al's calculator should help you set the steps per unit correctly; http://www.machsupport.com/forum/index.php?action=dlattach;topic=16315.0;attach=23771

Tweakie.
Title: Re: Problem to setup a belt driven 4th axis
Post by: joeaverage on April 26, 2018, 04:40:35 AM
Hi,
a rotary axis is tuned to so many 'steps per degree'. Thus if you have your stepper set for 8 microsteps or 8 x200 =1600 steps/ motor revolution.

With a belt reduction of 4:1 then 4 motor revolutions or 4 x 1600 = 6400 steps per A axis revolution or 6400 / 360 = 17.77 steps per degree. You will have to round to
18 steps per degree but that would result in an error of 1.2%. Not bad.

If you work backwards you may be able to reduce that error a bit. If you assume 18 steps per degree then a full A axis rotation would reuire 360 x 18 =6480 steps.
With the same 1600 steps per motor rev you would require a belt reduction of 6480 / 1600 =4.05. Thus if you have a belt reduction of 4.05:1 instead of 4:1 your steps
per degree would be perfect.

A pulley of 20 an a pulley of 81 teeth would do the trick.

Craig
Title: Re: Problem to setup a belt driven 4th axis
Post by: cncman on April 26, 2018, 06:15:29 AM
Thanks everyone that tries to help me! Craig, i was close to your solution but i was not 100% to this point! Thank you very much, i really appreciate!
Vasili