Ok so my cnc is generally great (for my very very simple needs!) but it does have 1 major failing that i would like to improve. The gantry is made up from 2 20mm round bars spanning approx. 7-800mm and it supporting a 1.5kW chinese spindle and associated mounts. You can imagine what happens - tons of flex/ruined parts - most noticeable when trying to cut sharp 90 deg turns from y to x, ends up with a lovely big curve if I go to fast!

Here is a rough diagram.
Click image for larger version.  Name: Drawing1.jpg  Views: 350  Size: 25.5 KB  ID: 10489

I also had a situation cutting a long thin pocket running down the x axis - all was going fine until suddenly the spindle seemed to flex down as if was trying to dig into the wood! I guess this was the flexing issue allowing this to happen...

So my question is how could I possibly improve my situation with minimum cost/rework?

Two ideas I thought of are:-
* upgrade the round rail to a larger diameter.
* change the round rail to supported round rail - I was thinking I could grid off part of the support at each end of the rail so it would fit in the existing holes?

Any ideas?