If you want to cut steel efficiently then I'm afraid the machine will need to be significantly stronger and consequentially more expensive. My subsequent comments are based on the assumption that the majority of the parts you want to cut are steel.

Do you actually need 200x200, or would about 140x300 be acceptable? If so you could just convert a milling machine to CNC. Get one second hand and it could well be cheaper than making the CNC router strong enough. I got my milling machine on eBay for £320 (add to that price of ballscrews etc), compared to about £1k new...search by distance nearest and if you're prepared to wait something's bound to come up.

Quote Originally Posted by m.marino View Post
if you plan on using precision profile rail that means you will be needing around 200mm width of the z plate to mount them
Which linear rails are you planning on using? Profile rails are pretty much a must to cut steel. You might get away with SBR25 supported round rail, but it will be mediocre by comparison. You should be able to fit two 15mm profile rails in a 150mm wide Z-axis quite easily so long as you don't use flanged bearing blocks. Profile rails can have fairly good seals on the bearings, but it's still best to protect them particularly as the only way to get rails for a good price is second hand where you can't specify the correct seals/scrapers.

'500+ oz-inch motors'

Common misconception that you'll need big motors. You wont need more than 3Nm. Compared to say woods and plastics steel is cut at very low feedrates and the machine is small, so high rapid speeds are irrelevant. Most motors greater than 3Nm are Nema 34, so they're unlikely to go faster anyway. There's a lot to work out first before considering buying motors!

What spindle are you thinking of using? The standard spindles for CNC routers are no good for steel as they are optimised for high rpm. On mild steel I doubt you'll ever need more than about 3000rpm. Making your own spindle is probably the best bet.

Do post a drawing when you've considered the changes that have been suggested.