We can only officially support the sizes offered through our website (1000x1000mm) as we have built and tested these ourselves. For those new to CNC and 3D Carvers, it might be safest to start with one of our stock machines and follow along with our instructions for your initial build, and then go from there.
For those who want to go this route, the best place to see how others are expanding their stock machines would be on our forum. Here are a few forum posts that will get you going and are good examples of what people are doing to expand their machines:
Upgrade 1000mm To 1800mm X axis Rail
Expanding the x-carve size(bigger then 1000x1000mm?
The size of the machine is determined by the Makerslide rail. We do not carry rails longer than 1000mm. There are some attempts on the forum to make a larger size by connecting two pieces of Makerslide end to end. However, with this technique, you end up with a seam that could impact the quality of your cuts. If you go larger than 1000mm in the X-axis direction without modification, you'll start to see some deflection, and 1000mm is the longest length of Makerslide we have available.
We encourage you to reach out to the awesome and wonderful community on our forum. It's full of extremely helpful individuals who are more than happy to help modify your machine.