So, an update.

I managed to epoxy the gantry to the main body. Scary stuff this. Will some 'glue' hold an estimated 750 kg weight? Seem it does.



Next step was to rotate the mass and remove the table as I needed access to the rails.

Ignore the loose rails in the middle of the lower part.



I then, with a lot of effort, lift my 300 kg 'reference' onto the rails, align and mount so that I can use this to get the epoxy set against the gantry.





The nett result is that I have something that moves forwards and backwards that is aligned to the bottom rails and should therefore be square once moulded. I should be doing the epoxy pouring this weekend.

Some of you might note that the reference part is only 50% of the width of the gantry. I dont have a larger reference surface and using it on its side means it will be too low.

So two options. I can either mould this width and then use a surface plate that I have and basically overlap until I get the full width.
Second option (and what I have gone for) is to basically put 100mm wide (the rails are only 40 but I need some extra height for the adjustment up and down) 30mm thick alu tooling plate (Eco Cast). I know its not perfectly flat but I am hoping this will be reasonable. Ill bolt this to the reference square and see how this looks.

https://youtu.be/ZtDXA0xAFhQ