# Gonna need some HELP!!!!!  Gear ratios



## Charley Davidson (Aug 5, 2012)

I'm planning my motor mounts and gearing so I'll need some expert help as I only want to do this once.

What info do you need to calculate what gear ratio I'll need? 

My steppers are 640 oz, 4 phase, step angle deg/step 1.8 

The thread on my Z axis is 9-10 per inch

My gantry Y axis is a hauser linear drive hle100 you can google and get a pdf with all the specs

all the info I have at this time.


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## Rbeckett (Aug 5, 2012)

CD,
What stepper boards are you using?  and how are they set up?  If using microstepping or small steps it will make a diff in the calculated gear ratio and ultimately the position of the tool also.  Hope this helps.  My 5980 X feed is just a simple motor drive, but if you want DRO or CNC it will make a difference.  When you decide look at Motiontek.ca for parts and pieces.  They have a ton of off the shelf set-ups.
Bob


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## Charley Davidson (Aug 5, 2012)

Here's pics of the documents I got with the steppers/drivers I did not include the Bob papers but can if needed


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## Charley Davidson (Aug 5, 2012)

Duh!!!:nuts:

This might be better


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## Rbeckett (Aug 6, 2012)

CD,
I think 4:1 would be good for the size motors and pitch of your screw.  Mach 3 has the capability to be programmed to accomodate the ratio and you would get adequate mechanical advantage to overcome the inherent torque in the system.  You would also gain the capability to vary your speed for different surface finishes.  Are you using low lash ball screws or basic components?  Ball screws are much less affected by lash and can therefore be used in both directions to move the tool in and out like following a pattern with a high degree of accuracy.  I'm really looking forward to your finished table, the initial stuff looks great already.
Bob


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## DMS (Aug 6, 2012)

Most people I have seen that use steppers go direct drive. The reason being that steppers have great holding power, and low end torque, but torque drops rapidly as RPM increases. If you gear up to increase your torque, your usable speed is going to be very low.

Given the pitch you list, it looks like you are using acme screws? Ball screws are more efficient, less friction, so more of the power you put into them goes into the table. Also, depending on the pitch of your screw, you may be going fast enough direct drive (ball screws tend to have a larger pitch than acme screws).

Another thing to think about is that you have pretty fine steps (1.8deg). That means you have to pulse 200 times per revolution (assuming you are not doing micro stepping). There is a limit to how fast you can reliably deliver pulses from your computer, and that is going to determine your maximum RPM. EMC has a way of checking this out, I assume Mach 3 has something similar. Maybe somebody more familiar with M3 can chime in.

The one nice thing about going with a belt drive is that you can fiddle with the ratio if you find you need a little more speed, or a little more "oomph" down the line.


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## brucer (Aug 8, 2012)

charley,



 I chose the 4:1 gear reduction.. I used 15tooth and 60 tooth timing belt pulleys, It's easy to go to 3:1 ratio by just swapping the small pulley to a 20tooth for 3:1 gear reduction..

 If i were building a plasma only machine i would probably start with 3:1 gear reduction, I'm planning on routing/milling so I went 4:1 gear reduction.. 

since you have a 10tpi pitch on your z axis I would probably just hook your z axis up with a zero backlash coupler for starters..

 microstepping is related directly to your motors rapid speeds and your machine resolution,  basicly transforms your 200 steps per rev stepper motors into 400/800/1600 steps per rotation and so on...  You will loose speed with greater number of microsteps, but the greater number of steps the better your resolution..   your gear redution also will play into your machine resolution...

  i also found a nice video and page that explains it well.. 
http://www.youtube.com/watch?v=6vY26CIrVwg  and http://www.joshuaglenn.com/jgblog/index.php/topics/diy-cnc-router-and-cnc-machine-tutorials/

 hope it helps..


 dont over think it.  I would use 4:1 reduction on the x and y axis, and use a zero backlash coupler connected directly on the z axis to start with..  if you using a belt reduction, the small pulleys are cheap and all you'll need is 2 or 3 of them depending on how your driving your gantry....


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