Yes I was thinking of an adjustable 'Z axis', the diagram of the table was only a rough idea.

I'm thinking a basic frame 75x75x5 with the braces out of 50x50x5. I'm looking to cut 6 and 10mm mostly maybe some 12mm sheets so I need to build a table braced to support a 12ftx6ft x15mm sheet if need be I will increase the sizes or just make it all outta 75x75x5???

The image of the table I attached had a .dxf file of the slat support designs I must redesign these to suit the size of table I go for and I will price them for cutting in a local engineering shop.

My biggest problem of the whole build is the motors and the rails setup. The fabrication of the table and the separate supports for the gantry is the reasonably easy part?

Do I have to buy the rails as a one piece or can they be joined?? Also how many do I need??

https://youtu.be/vETkf1sqo3M
This lad used angle irons and rollers like a roller gate set up for the liner rails will this system work?? is it a cheaper method??

Thanks again for the replies its great seeing that people are willing to talk and share there views.