This is my first BUILD please help.

[EddyCurrent]

Please do not take my comments as critisism because your machine is excellent, it's just that for me there looks to be a mismatch between the gantry and bed frame.
Well I'm no expert on rails but from what I've read and found with my own machine I think you would have done better using the low profile rails such as Hiwin. Lots of people use the rails you have and they seem to work well but somehow they are not in keeping with that substantial base. Hiwin rails however would have been more expensive.
There 's one thing for sure though and that is the frame and bed will have enough stiffness.

As an experiment maybe you could add some test results to this thread ?
http://www.mycncuk.com/forums/gantry...cnc-mk3-2.html

[JAZZCNC]

The biggest problem with the round type rail and esp the cheap chinese type is the bearings quickly become loose and sloppy so lose accuracy and need regular adjustment.
They are no where near as accurate to start with compared to profiled linear rails which just work and last for years without any attention other than lubrication now and again.
They won't take the abuse Profiled linear rails will take and dusty or abrasive conditions will quickly take it's toll on them unless you take precautions to protect with wiper seals etc.

Like Eddy I agree these rails let down what looks like a nice substantial machine and IMO Profiled linear rails make the difference between Average DIY and Professional machine.
Don't look at it so much in terms of they are expensive which they are not in long run because they give a much better and far more reliable machine but more they will return there investment 2 fold later down the line if you ever decide to sell the machine as they will still work just the same and not be wornout plus appeal more to potential buyers who are prepared to pay more for professional looking machine fitted with correct components.