Recommended Co-ordinate system

[St Taw]

My corexy machine has a motion area of 350 in X and 330 in Y.
Currently when it homes the co-ordinates are defined as 0,0 at bottom left hand corner.
The bed location starts at about 25 in X and 0 in Y and is 300mm wide.
In the Y axis the usable bed area is to 280. Beyond that is for tool change.

The question I have is would it be better in the long term to define the home postion in X as -25 so the bed area starts at 0X, 0Y. If so what method of defining this is recommended as I imagin there are several ways of doing it in G code.

On a related note my Z axis homes to an optical sensor and this is defined as 0Z. However in order for the nozzel to touch the bed it needs to go to about -5Z. I could move the optical vane or could define the homed location as +5Z. Again several ways of doing it. What is recommended?

One final question. Because of tool change collection and parking the head moves in effect outside the bed area. Is there a way of defining allowed limits of motion during the print process which can be turned on/off during the tool change. The rational is that if the print g codes attempted to go outside the bed area (which would be allowed because of machine area) it could damage the tools.

Thanks.

[DocTrucker]

I've recently swapped to setting the machines so 0,0 is bed centre.

It's really personal preference. (0,0) can be limits, edge of bed, centre, or anywhere else. It only really matters when it comes to making sure your slicer knows the printable limits so there's no thought needed about ensuring parts are on the bed.

Z=0 on the other hand is normally set so that all things being equal the nozzle just touches the bed. Additional travel is allowed to compensate for a wonky bed.

To temporally change the limits you could do just that, change the limits of travel in the macro then reset them at the end. The question would be why do it? If you have set up your slicer to clearly show the printable area then that should be all that's needed.

Also be aware that the limits aren't always respected. I think it is doing the bed probe using bed.g rather than the mesh it ignores the limits. That may not be the only time limits are ignored.

[wilriker]

I was starting out with X0, Y0 being the front left corner of the printable area, i.e. the print bed. That also meant that homing positions for X and Y were in negative.
I temporarily moved to X0, Y0 being center of the bed but that always gave me headaches figuring the positions out because my brain just works in terms of 0 being at an edge. So I returned to what I had before (and since I only have one machine the argument for GCode being better portable between machines does not count for me).

But as @DocTrucker said it comes down to personal preference. I can also confirm that Z=0 usually means the nozzle touches the bed so I would change the height after homing at the end of the homing macros. If it is reliable at Z=5 I would not move the sensor.

[dc42]

I too set X0 Y0 to be bed centre. This lets me print the same GCode files on 2 Cartesian machines, 1 delta and 1 Scara.

[St Taw]

Thanks for replies.
Think I will go with bed centre being 0,0 before current setup gets too ingrained and see how it goes.