Cutting metal

Years ago I did a CNC fusion kit conversion of a Sieg X2 with an eye to milling aluminium parts for my race car. I now have a Sieg KX3 - a beefed up, factory CNC version of the SX3 that I got near new at a bargain basement price....

The bottom line is that the sieg mills just aren't designed for _regular_ milling of metals. The spindles are not powerful enough, and while the KX3 is far more rigid than then SX3, unless you are really careful and take small cuts the head still vibrates enough to cause chatter even on soft aluminium.

So while you can make decent parts from aluminium and various steels with sieg mills, it takes lots of time and care and many prototypes to dial in the feeds and speeds necessary to minimise vibration and chatter to get the desired accuracy and tolerances in the milled part.

Hence I think the most important question people looking at CNC mill conversions have to answer is this: do you just want to "learn CNC milling" or do you need a CNC mill to make parts for other projects?

If you just want to "learn CNC", then great - buy a second hand sieg mill off ebay and a conversion kit and off you go. That's exactly what I did with the X2. But be aware that you'll quickly outgrow it's capabilities if you want to do any serious metal milling with it - I found the X2 really couldn't mill aluminium with better than ~0.5mm accuracy or repeatability even after substantial modding to improve rigidity, minising play in the table, etc. Hence it was only as I graduated from "learning CNC" into "building other stuff" that I realised I'd started with the wrong mill for what I really wanted to do with a CNC mill.

Which brings me to the other side of the coin: Sieg mills really aren't that cheap. Here in .au, you can get a decent low end Hafco industrial mill/drill with a 1.5-2kW spindle with the weight and rigidity of a KX3 for not much more than a new SX3. These will do a much better job of milling metal than an SX3. And for a bit more $$$ you can get a really solid, good quality industrial mill that will perform far better on metal and run more reliably for longer than any heavily modded, high end hobby mill will ever do...

Hence before you start on your CNC mill adventure, decide/know what you are actually going to do with the CNC mill once it's built. Then go and buy a mill appropriate for that job rather than something that is cheap or "simple to convert". Finding out you can't do what you want to do with the mill after the conversion is complete is not much fun....

-Dave.