Newbie- Gear or Timing Belt System for new CNC

[CHESS IS GOOD]

Hi Guys,

I am a newbie. I'm trying to built my own cnc machine. I have read on how to select the different ballscrew and nut. The only thing left is the connection. From what I know that are 3 different types of connection
1. Direct Drive
2. Using Gear
3. Using Belt

What are the benefits of using gear or belt system ? How would the gear or belt system effect my calculated results based on direct drive ?

[LeeWay]

They would give you more torque and resolution and allow for more misalignment of the motor. They usually take up less real estate because you can tuck in a motor, where as with direct drive, it sticks straight out from the screw. Good couplers can cost about half what a good timing belt drive would cost especially on smaller pulleys and belts.
You can better fine tune your machine with a timing belt drive.

I use both direct drive and timing belts on various machines I have built. I think it really boils down to budget and what kind of performance you expect as well as how heavy your axes are.

Several other things will also help define your needs. Power supply, motor size, drives, and what sort of linear motion system you use.

[CHESS IS GOOD]

Thanks Lee Way,

Can you clarify on the more torque. Is it for the direct drive, belt or gear ? What drive system do you suggest for a load of 20kg - 50 kg load ?

As for the spindler , If you need to do milling on steel what king of torque and rpm would be good. Some say rpm around 3000 RPM but never suggest on the torque.

Can you help me on this ?

God Bless
Eng Huat

[Coogrrr]

you increase torque as you change gears or change pulleys with the belts. I built a belt driven one and effectively doubled my torque by running a 2" main pulley and a 4" drive pulley with a timming belt. I got finer resolution out of this also but it effectively cut my IPS in half which was no biggy for me as the steppers and such are able to move up to 300ips anyway so I keep it near 100ips with a ton of torque.

-Coog

[Al_The_Man]

Belt reduction is cheap but only practical for smaller ratio's anything larger than say 10:1 and up, a planetary gearbox is more efficient, it is not so much the load itself it is the rate you want to accelerate it that has more bearing on motor size.
Torque is increased by the ratio of reduction and inertia ratio is increased by the square of the reduction.
The industry standard is to aim for no higher than motor to load inertia of 10:1.
See post #13 here:
Calculating What kind of power i need ????
And the attached PDF it refers to.
Al.