Axis home with index wiring

I'm attempting to sort out the homing on my new machine build and due to the large variation in trigger location with the mech switches I was planning to add an index to each axis using a photointerupter on a single tooth disc on the end of each stepper, aiming to search for home then slow down and finally stop and home at the index.

Unfortunately, as I only have 5 inputs and want to drag in spindle speed and a touch probe I'm probably going to need another BOB. My question, having not tried yet, is can the homing process be customised a little - i.e. home one axis at a time and move away from both switches once home reached on each axis? My thinking is
X search for home
X find home
X search for index
X Stop at index
X Move 20mm away from both
Y.....

This way I could run 3 axes from 2 inputs, paralleling all sensors. Unless someone spots something. So far I'm not up to speed on where such customisations would need to be incorporated.

HI

Regards homing, you can home one axis at a time and specify an offset from the switches

You can also use an index pulse, but not unless the axis stepgen is in velocity mode

www.linuxcnc.org/docs/devel/html/config/ini_homing.html

I always chain all the limits together if using a BOB, so 6 limit switches and 3 home switches only take up 4 inputs

The answer might be to get better home switches unfortunately, you can get away with cheap limits, because you should never hit them
but home switches are essential for repeatability.

I tend to buy secondhand good industrial ones or make proximity switches from hall-effect switches potted into hollowed out
threaded rod, actuated by a small rare earth magnet embedded into the table at a suitable point

These proximity switches work very well, so long as you mount the magnet somwhere it is not going to attract swarf.
The detection angle can be set by how deep the hall-effect switch is set into the steel rod.

regards

ArcEye wrote:

You can also use an index pulse, but not unless the axis stepgen is in velocity mode

www.linuxcnc.org/docs/devel/html/config/ini_homing.html

Thanks for the reply.

I'm afraid this doesn't mean too much to me at this stage (I'm not new to robotics or sensing (or RTAI software!) but I'm new to linuxcnc) - I think I understand the difference between the two modes but I'm unaware of how that will affect my homing procedure at this point. Initial reading has me confused, does that mean I'd have to be travelling between two fixed points within a machine-designated path and catch the home position on the way by, rather than stepping increment by increment?

I'm very wary of hall effect sensors, though they were my initial choice - I've used them in the past on unrelated projects and found significant variation in sensing distance with a number of variables (temp, contaminents, surrounding "stuff"). However I'm not sure how this differs in operation from a slotted optical out on the rear shaft of the motor, other than this complication of having to be in velocity mode which I'm not sure of. On a rotary encoder the positional sensing error should be lower (1 rotation = 60mm of linear motion at the circumference with some tolerance on the sensor (say 0.5mm for argument's sake) - that's <1% on the rotary sensing but 10% on the linear if the ballscrew pitch is 5mm).

Thanks for your time!