The relationship of limit switches to home switches.

[MikeAber]

I am building my first small gantry mill and would like to understand the relationship between the home switches and the limit switches better.

Is there a standard offset in distance between the home and limit switch positions? What is the typical distance?

Is the purpose of the home switch to tell the machine control program to ramp down the feed rate from a rapid return to home and then move to the home position for that axis?

How do I decide where to position the limit switch in relationship to where the axis will crash?

[trubleshtr]

Hi Mike, think of limit switches as the the furthest point you would alow the axis to travel, there is usually two one for furthest + travel position, and the opposite for furthest - position. Most machines have "hard stops" that will not let the axis run right off it's guides, the limit switches are normally mm or inches before the hard stop depending on the accuracy of your machine and speeds the axis is moving at.
Home can be any point you decide to use, some builders refer to it as a "safe position" althought there can be both a safe position and a home position for an axis it just depends on what your application is. Most machines use the "reference" position for the axis motor/encoder as the home position, but it can really be anywhere you want

[trubleshtr]

I forgot to add, your cnc program will control where the axis moves to, you do not have to run the axis onto a limit switch every time, rather use it as a moniter system to tell your machine controlls to stop movement if the axis comes into contact with the limit switch, if the switch fails, then you have the "hard stop" to prevent your machine from free wheeling itself onto the floor.
Your cnc program will control how you ramp up and down the axis. Home position, is simple a set of XYZ co-ordinates you pick, and when you tell the machine to go home it returns to the XYZ position you have determined. YOu can use a limit switch to creat redundancey for the control to confirm it is indeed at the home position, but I dont think this is necessary for a hobby machine?

hope this helps

[CJL5585]

In a large production environment where CNC's are set up to mill the same part over and over again, the home switch can be used as the ORIGIN position since normally the setup of the machine is a permanent one. A locating pin, etc. is located on the setup origin so the home switch position can be checked or reset to x=0 y=0.

This might not answer your question, but a home position switch is NOT A REQUIREMENT on most hobby machines.

Jerry

[MikeAber]

Thank you very much for your help!

I did find exactly what I wanted to know in the MACH2 Mill documentation along with several examples of how to install and implement the use of them.