# Thread: Ametek motors and step down ratio

1. ## Ametek motors and step down ratio

I have bought some Ametek motors from Kevin (some of you may also know him as you have bought motors from him as well)

I am trying to do a preliminary step down ratio for my motors which will be used to cut 3/4" plywood. I want a maximum rapid speed of 200ipm. Kevin suggests to run them around 1000-1200rpm with a step down ratio of 9:1.
This is what I have done to calculate the step down ratio but I do not know if it is correct:

Max Rapid = 200 IPM
Assume: 1" drive pinion (OD) (Radius = 0.5")
Circumference = 2*Pi*R = inches/rev = Pi for my drive
TPI = 1/(inches/rev) = 1/Pi = 0.3183 (# Revs to move 1")
IPM = (Distance/rev)(rpm) = Pi * 1100rpm = 3455.75 ipm (this rpm is what you said to run it at)
Step down ratio: (200ipm)/(3455.75ipm) = (1/17.279)

This means I need a 17:1 step down ratio

my gantry weighs around a hundred pounds

One last thing is would you run a the same step down on both y and x axis? Why or why not?

I appreciate any help. Thanks

2. If you get 1 inch of travel for every 3 revolutions of the motor and the maximum motor speed is 1200 RPM then divide 1200 RPM /3 Revolutions per inch and you get 400 inches per minute for a 1:1 or direct motor to screw coupling.

Now look at the the maximum speed that you can turn the ACME or ballscrew and stay below the max. speed for the screw. Adjust your calculations.

You also need to consider torque when deciding on a gear ratio or coupling ratio.

3. ViperTX, he gets 1" of travel for every 1/pi revs of the motor.

dowling, your calculations looks correct to me. Kevin's suggestion of 9:1 ratio is probably due to the fact that it can be achieved with two 3:1 timing belt reductions (i.e. relatively easy to do). If you get enough force with this ratio, then just limit your motors to 600 RPM, or enjoy some 380 IPM rapids! Otherwise, perhaps you can find a planetary gearbox with a higher ratio on Ebay, for example.

There's no particular reason to use the same ratio on different axes, other than that perhaps it's easier to build several similar reductions.

Arvid

4. As we have established b4, I have the same servos as you. I drive mine at 3;1 ratio and it works fine. The only reason you would want to reduce that further is to get more torque and greater resolution.
If you are new to this, you may be thinking, as I did, that the gearing down factor was a crucial part of the project. The software you use will play a part in terms of setting the maximun speed. Esentially any reduction between 3;1 and 9;1 should be fine. The main aspect of knowing if you have a good reduction is the size of your router, and its ability to cut at the desired rate. Once you play with the software configurations and understand what every thing does, and how it all interelates, the penny will drop and you will understand that the gear ratio is not as crucial as you might have first thought. I know you want to be told a definate number, but trust me if you go for anything between 3:1 and 9;1 you will be right

• Originally Posted by dowling177
I have bought some Ametek motors from Kevin (some of you may also know him as you have bought motors from him as well)

I am trying to do a preliminary step down ratio for my motors which will be used to cut 3/4" plywood. I want a maximum rapid speed of 200ipm. Kevin suggests to run them around 1000-1200rpm with a step down ratio of 9:1.
This is what I have done to calculate the step down ratio but I do not know if it is correct:

Max Rapid = 200 IPM
Assume: 1" drive pinion (OD) (Radius = 0.5")
Circumference = 2*Pi*R = inches/rev = Pi for my drive
TPI = 1/(inches/rev) = 1/Pi = 0.3183 (# Revs to move 1")
IPM = (Distance/rev)(rpm) = Pi * 1100rpm = 3455.75 ipm (this rpm is what you said to run it at)
Step down ratio: (200ipm)/(3455.75ipm) = (1/17.279)

This means I need a 17:1 step down ratio

my gantry weighs around a hundred pounds

One last thing is would you run a the same step down on both y and x axis? Why or why not?

I appreciate any help. Thanks
Nevermind.

• Thanks Ynneb for the info, I did not realize that the software aspect could play a role. I got one more question for you. For my z-axis i obviously do not need to step that down by a 9:1, i have an 8mm lead ball screw, by what ratio approx or what range of ratio's would i need to step step that down to plunge through wood?

thanks