Homing switches & 'methods of working' (Mach3)

[Wobblybootie]

Thank you all, I am nowhere near ready to deal with the physical problem of limit switches (still amassing parts) but I do ponder things like that when I get 5 minuets of quiet time. The problem was clearly laid out and the solution was just as clearly explained. This forum is worth it's collective weight in gold.

[John S]

One thing with CNC is there are no real right or wrong ways, just different ways of doing things

Some people use limit switches as homing switches and then use G54 to go to the work zero.
Homing switches take you to MACHINE CO-ORDINATES then using G54 this takes you to WORK CO-ORDINATES which is usually the corner of the work or vise. Many newbies have a lot of trouble with differentiating between the two.

A simple way to start is to use the corner of the work / vise and set both co-ordinates to this point and not use homing, a ref all or goto home will then use this same point.

It's purely personnel choice.

One final note when drawing parts to be used in a vise, The normal way of drawing which dates back from the old manual drawing board days is to use the bottom left corner as 0,0. This then makes all dimensions / moves positive but a CNC doesn't have to worry about this.

If you make this point 0,0 then it puts, on a normal setup, the origin point on the edge of the moving jaw. Any differences in blank size will make all the parts different from it's true 0,0

If you use the top left as origin it then puts 0,0 at the end of the fixed jaw and every part will be identical regardless of blank size. Most CAD systems give you the option to move origins so no matter how you draw on the last save you can set this to top left.

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[Wobblybootie]

Cheers John, that makes sense and logical really, just never saw it like that. Yet another nugget of information to be stowed away.

[reuben005]

Even i am doing the exct same thing, with the 2 limit switches on the min and the max end of the axis, and the home somewhere in the middle. Even i am using the Work offset option.

The only problem i am having is that when i click the "Ref all home" button, sometimes the tool is at the negative side of the home switch and it keeps going negative until it hits the limit switch and the machine shuts down. Now i have no way of telling the machine which side of the home switch the tool is.

so any views?

[C_Bubba]

Even i am doing the exct same thing, with the 2 limit switches on the min and the max end of the axis, and the home somewhere in the middle. Even i am using the Work offset option.

The only problem i am having is that when i click the "Ref all home" button, sometimes the tool is at the negative side of the home switch and it keeps going negative until it hits the limit switch and the machine shuts down. Now i have no way of telling the machine which side of the home switch the tool is.

so any views?

This is why you put the machine coordinate at one of the limits of the axis. That way the Machine will always home in the proper direction. From there, you set your offsets for the various fixtures as previously noted. Fixture offsets are your friend! When you make a setup, you have the option to "save" the offsets. Now if you have a crash, power failure etc. You can simply restart the machine, home it and load the offsets and your back in business with no additional setup time. Sure, it may take a few seconds longer to make the setup, but it only takes one time to see how useful this can be. (Don't ask how I know:})

[audioandy]

Even i am doing the exct same thing, with the 2 limit switches on the min and the max end of the axis, and the home somewhere in the middle. Even i am using the Work offset option.

The only problem i am having is that when i click the "Ref all home" button, sometimes the tool is at the negative side of the home switch and it keeps going negative until it hits the limit switch and the machine shuts down. Now i have no way of telling the machine which side of the home switch the tool is.

so any views?

The only thing I can think of for a work around on this is at the end of your G code when your tool maybe goes to X0 Y0 Z30 (example only) you can change the code so your axis finish on the positive side of your home switch so X50 Y50 Z30 (example only) then when you reference you should be ok.
Other than that move your home switch to the Neg side of movement on your X and Y axis.

hope this helps

Andy