Building a cnc router

[Steven Smith]

Something like the Kronos can cut aluminum successfully, however it may require a little tuning. Plastics/wood are generally much more forgiving in terms of feed rates, and you should have enough power and stiffness to make short work of them.

Essentially though, a gantry mill analysis is no different than any machine when you're looking at what you can cut successfully. In order to cut something, you need a combination of sufficient rigidity in your machine and sufficient power to make the cut. If your machine isn't rigid, the bit will bend off the cutting surface (rub on it), or chatter in and out of it. If you lack the power, well, you'll find out that out quickly

Gantry mills are pretty awesome in that they can be reasonably cheap for such a large work surface. It comes at a compromise though. It's harder to make a large span as rigid as a small one. Also, the larger you make your gantry (the moving part with the router attached) the more power you need to accelerate and decelerate it. Routers are a great and reasonably cheap tool head. However, they natively spin at a very high RPM (20K range). When you do the calculations for how fast you need to feed material to constantly take a bit enough bite of material to not chatter, you're moving fairly quickly through material. This can generate a cutting load of 25-50lbs+ resisting the bit, which at the best case generates inaccuracy, and at the worst case, results in chatter/broken bits.

At the end of the day, you can always just choose to take a shallower cut, (0.03" to 0.05" passes aren't uncommon), which allows you to move through the material quickly enough to maintain chip load, but minimizing bit deflection. So many machines can "cut aluminum", but the more rigid ones will do so more accurately and more quickly.