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### Author Topic: Problem to setup a belt driven 4th axis  (Read 1175 times)

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#### cncman

• 24
##### Problem to setup a belt driven 4th axis
« 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

#### Davek0974

• 2,606
##### Re: Problem to setup a belt driven 4th axis
« Reply #1 on: April 26, 2018, 02:09:07 AM »
Simple - use pulleys with that ratio of teeth?

20 on one, 80 on the other etc

#### cncman

• 24
##### Re: Problem to setup a belt driven 4th axis
« Reply #2 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.

#### Tweakie.CNC

• 8,917
• Super Kitty
##### Re: Problem to setup a belt driven 4th axis
« Reply #3 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.
PEACE

#### joeaverage

• 6,884
##### Re: Problem to setup a belt driven 4th axis
« Reply #4 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
My wife left with my best friend...
and I miss him!

#### cncman

• 24
##### Re: Problem to setup a belt driven 4th axis
« Reply #5 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