# Thread: pulley ratios on 3 pulley axis

1. Ok guys just got myself very confused. I have the following configuration setup on my X axis
5mm pitch HTD15 belt used:

16 tooth pulley on stepper going to a 72 toothed pulley, on the same shaft as the 72 is a 24 toothed pulley driving the axis with matched 24 toothed idler. What by your calculations should the ratio be? Things are cutting slightly larger than expected in EMC2 :whistling:

2. Doesn't make sense.

16 driving a 72 with a 24 on the same shaft, OK, now is the final pulley a 24 in which case it's not an idler but driven.
And if the 24 is an idler then you haven't told up the final driven pulley.

If the first then it 4.5:1 reduction

3. Hi John

I only mentioned the idler for completion. It 16 to72 then 72 to24 which my reckoning is 4.5:1 then 3:1. the total being? this is where im lost :-(
Last edited by Swarfing; 20-07-2011 at 01:17 AM.

4. Still doesn't make sense.
In the first post you state " on the same shaft as the 72 is a 24 toothed pulley driving the axis with matched 24 toothed idler."

Now you are saying "16 to72 then 72 to24"

So have you got a 72 and a 24 on the intermediate shaft or two 72's ?

5. So am i right in thinking (starting with the stepper end) you have geared it down then back up again? :S 16---72----24

6. ok a picture speaks a thousands words

this should make it easier to understand

7. ( Deleted what I had posted here as posted at same time as previous)

It's 16 to 72 then, which is (as JohnS said) 4.5:1 or 0.2222=2/9

The 24T pulleys just link the two screws so are irrelevant.

8. Right so looks to me like 16 driving 72 with a 24 on the same shaft driving another 24 ? [ not in picture ] ?

If so the two 24's cancel out at 1:1 and the 16 to 72 gives a 4.5 : 1 reduction x by 1 : 1 is still 4.5 reduction.

9. Cool that is what i was hoping you would say, shall change the config tonight and give it another go. As you can already guess i was trying to do something with the gear up scenario which does not exist.

If all is well i will take some proper pics and post the results :-)
Cheers guys

10. Here's the update so far, the config set up as 4.5:1 got me closer. over a distance of 150mm on screen the actual travel was 173.5. I've never set up belts before so what next? play with the ratio or the number of steps per mm? it seems a lot to play with the steps. Im using quality pulleys an belt.

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