Thanks for the input guys.
The Mech mate has a slave on the x axis with two rack and pinion stepper motors. I used the cutting of two boards and turning one over technique to determine trueness of the straight cuts (within0.2mm) and squareness (approx 0.8mm per m out but plus or minus half depending where it is switched on. I can adjust most of that out, just take another couple of it will require reseting the Z squareness and resurfacing the table.

The way I am thinking if I cut all formblocks from the same side no issue with fairness and the part must move a mm, anyway should do the correction in a couple of weeks.
It is very hard to prove these home make machines are better than a mm accuracy in their length. When I started the testing they were about five percent out because the chinese gearboxes were not the ratio advertised, That took a while to prove...

Thanks for the hints about working with quality foam and the heat it can handle. It is so much easier to follow than lead.

Plans should be here in a couple of weeks so on with the "honey do list"