Z home problems now seen on two of my CNC machines

When tring to home the Z Axis I get a problem with this messages "home switch inactive before start of backoff move" and the message "home switch active before start of latch move"

I first tryed to use EMC on this little 3 stage machine bodgeitquicktools.blogspot.com/2009/05/t...owered-workshop.html

I put this project to one side thinking it had a faulty embeded micro switch.

I moved on to a slightly bigger machine in light of the problem with the micro switch. I decided to use infrared opto end stops as used on a reprap 3D printer.

X and Y home exactly as expected on the bigger machie as the did on the tiny machine however Z will only some time home mainly giving the fault condition mesages "home switch inactive before start of backoff move" and the message "home switch active before start of latch move"

I re wired the opto swich with Shiilded cable ( an old USB lead) as I suspected stepper motor noise giving false readings I also decoupled the supply with high an low value capacitors for high and low frequency noise.

Also swapping the input pin from 12 to 13 for the Z axis home switch. Replacing the opto sensor with another sensor board.

Neither of these fixes solved this problem Im not quite sure where to investigate next.

The Linux is Ubunto 8.04 from the CNC install CD from this site so the EMC version is 2.3.0 the mother board is an ITX Gigabyte Atom as it has a paralle port.

All ideas sugestions welcome.

Is there a file that you can adjust the sensitivity of the hysterise on the home switch?

Is this a known issue with the mother board Im using.. ?

Is there a way to de-bounce the Z home switch in SW?

Pictures of the full machine bodgeitquicktools.blogspot.com/2009/09/p...-rebulit-bertha.html

Problem solved, by increasing the size of the plastic IR blocking tab, after chasing many red herrings.

Switching noise caused by vibration from the stepper drives The tab needed to be 1/4" bigger to eliminate the problem.

Many thanks to BGlackin who posted a reply on my Blog I printed and read the Integrators Manual its a good long read but full of usefull stuff.

The sucess has lead to starting the 4' by 2' Big Bertha version. bigberthacnc.blogspot.com/2009/09/big-bertha-beginning.html