New router build advice...

[JAZZCNC]

Im more of a figure it out on the fly than a planner kind of guy but I understand the need for it in this situation so I'll get my head down.

Resist the temptation because it will cost you money and frustrate. Key to a good machine built within budget is planning along with careful research and asking lots of questions.

In terms of size, what sort of frame footprint should I be looking at to begin with and will I be ok with the 80 x 80 x 5mm steel box section, can I go smaller or do I need to go bigger? .

I cannot answer to what size machine you need only you can know that.! What I can offer is that if your chasing space then consider looking at a vertical machine. it offers a big space saving along with other advantages. See video

80x80x5 will work but wouldn't go less for 8x4 or 10x5. I use 100x100x6.

In terms of creating more mass to remove or dampen vibrations, is this why some machines will have additional weight added to the machine?

It's not so much weight more density that's required. Adding extra weight just costs money because takes more power to move it around. The goal is to reduce vibrations but doing that by making things stiffer and adding weight can actually introduce vibrations because becomes more resonant. Materials that absorb vibrations are more beneficial which is why cast iron is often used in machines.

What sort of size belt would I be looking at, they must be wide! Are you thinking of the usual single belt or would it be doubled up, is that even worth it? Do the issues with belt stretch still apply?

25-30mm will work. If you want the best system then follow the Everman type setup as it keeps belt stretch to a minimum. That said if you use the correct belts then it's not an issue.

Would it be better to look at an ally extrusion gantry to keep weight down if I'm looking at belt drive? Will belts not chase additional issues in terms of machine rigidity or am I overthinking it with the applications that I'm looking at?

Better than what.? Regards ally extrusion then that's what I mostly use on all my router machines for the gantry. It offers several advantages over steel when comes to fastening rails etc and is very good at reducing vibrations. It's also much easier to work with if you haven't got a mill or machines to help.