Still trying to make sense of this…
LaserGRBL:
Lightburn:
Report what is the same, and what is different between these two tests.
P.S. Tell us what Device Type you selected for your laser.
Hi Mike
So am I 
When following the instructions above there is NO difference. Both times the head stopped 1-2mm away from the X switch and the laser had to be manually turned off to stop the grinding noise and vibration.
However, on rebooting and reloading Laser GRBL, moving the head to the centre of the frame and selecting the Home icon, the head moved smoothly back to 0,0 and stopped against both switches.
When trying the same with Lightburn, the head did exactly as before - 1-2mm from the X switch it stopped and made a grinding noise etc. As I said to Misken, if I set the X=0 and Y=0, on the Move tab in Lightburn, and then Go To Position, the head goes smoothly to 0,0 and stops against both switches.
Here is the device as setup in Lightburn
Thank you again for all your efforts. I run a charitable association and all us volunteers make things to sell for charities so we can’t afford to get someone in to sort this and so your help is really appreciated.
Regards
Bob
Did you also reboot and reload Lightburn?
Actually, the answer does not matter. The Home cycle “it failed” with LaserGRBL followed by the “it succeeded” with LaserGRBL suggests a mechanical issue. It appears your machine is on the ragged edge of triggering the Xaxis switch. Othewise LaserGRBL would not have failed.
On the Xaxis switch, put 2-3 layers of masking (or other thick) tape on the lever of that switch. Test with both LaserGRBL and Lightburn.
Eagerly waiting for your Reply…
Hi Mike
Yes to make the comparison exact.
I’ll have to do this am tomorrow as I’m now part-way through a project. I’ll try that and reply tomorrow.
Thanks again
Hi
I tried that just now, and I even moved the switch 2mm across the bar, with the same result as before. In fact, when I moved the switch the head tried to force it back to the left !
I’m going to admit defeat and I’ll either remove the limit switches and go back to operating ‘by eye’ or use the Go to position 0,0 on the move tab.
The good thing is, since truying all the options, when the project is finished it goes smoothly back to 0,0 by itself and the Go To Origin button does the same rather than sending the head zooming off to the top right.
Thanks to everyone who has tried to solve this for me, your help was really appreciated.
Bob
I wish I lived close enough to you to show up with my DVM and digital scope. This makes it appear the switch action is not making it to the controller. But how does that switch know the difference between the two softwares? Or the controller?
If you do, we must also. I hate being outsmarted by a machine! 
In those immortal words “I’ll be back” 
