CNC Router Electronics?

[wmacdonald250]

Hello folks,

I am a bit new to all of this, and have a couple questions that I haven't been able to find an answer to.

I have the knowledge and ability to build the mechanical side of a CNC machine, however I am struggling with how this is intergraded with a controller and software.

For example, Say I build a CNC router with a table 8ft x 4ft, and a Gantry with a Z axis with 4" of vertical travel.

I install Stepper motors with sufficent power to drive all axis's.

How do I then configure controller so It knows its travel limits for each axis, as well as its location on each axis at all times?

Is there a controller package available that would work in this sort of setup, and can be programmed, or can "Learn" how much travel the hardware has etc.

Can anyone point me to a good starting point for this, I'd hate to build a nice big beautiful solid machine and then be unable to drive/control it.

cheers

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[ger21]

How do I then configure controller so It knows its travel limits for each axis, as well as its location on each axis at all times?

You install home switches on your machine, and when you turn it on, you run a homing routine, which sets a reference position on your machine.
Many controls allow you to specify softlimits, which the machine won't exceed. These softlimit positions are relative to the home position.

Most hobby or lower cost controls are open loop systems. They only know where the machine is supposed to be, but there is no feedback to tell them where the machine actually is.

There are a variety of control systems available, and all work similarly.
UCCNC
LinuxCNC
Eding CNC
Planet CNC
Mach3/Mach4

[awerby]

Even without limit switches you can define "soft limits" that prevent the machine from attempting to exceed its travels. But with the stepper motors we typically use on these machines, even if it does crash into the end of an axis (there should be a stop there to prevent it from sailing off into space) it won't kill itself; steppers will happily push against immovable objects all day without burning up or shredding the mechanicals. But don't try that with powerful AC servos - they will just keep trying harder until something gives.

[dharmic]

The Clearpath servos will detect that surge in torque when the axis hits the limit and can be configured to do a limit check based on that. No homing switches required. There's a lot smart about 'em, of course it comes at a price and I don't know whether you'd get Mach3 etc talking to them easily.

I only mention it as a different way of approaching control and drive.