I want to DIY.. some questions please!

[Tenson]

Is there a big advantage in build quality terms using profile rails for the Z-Axis rather than supported round rail?

I must admit I can't see an easy way to use supported rail so that the bearings oppose each other on the Z axis. I have seen Jazz used HiWin rails facing out, not opposing, so is this only okay with profile rail?

[JAZZCNC]

Is there a big advantage in build quality terms using profile rails for the Z-Axis rather than supported round rail?

I must admit I can't see an easy way to use supported rail so that the bearings oppose each other on the Z axis. I have seen Jazz used HiWin rails facing out, not opposing, so is this only okay with profile rail?

The advantage of profiled rails are much tighter bearing tolerences with a smooth action helping to reduce resonance and flex they also last much longer, esp in harsh conditions like a Z axis where it's constantly in the firing line and open to crap from the cutter. They don't really add much more strength than supported round rail if any.!

You can use supported rails just the same as profiled like you have seen me do. Absolutely no difference other than they stick off the Z axis rear plate (which you would call running across X axis, me Y axis) slightly more due to height of supported rail.