We have the Haas GR510. We have been using it daily for over 2 years now. It has been a very reliable machine, but I wouldn't use it for extensive milling in steel. We use ours primarily for drilling, reaming, tapping, 2D profiling etc. in aluminum. We had ours custom built with an extra 6 inches in height to accomodate a drill chuck.

I have done some 3D contour milling in aluminum, but I won't even try that in steel. However, drilling in steel is not problem, if your drill sizes are under 3/4 inch. Anything larger than that and we drill 3/4 and helical mill to size. For that application, it does well in steel.

Also, we find the accuracy pretty good for a 120" table. Over 120" we are out about .003". Not too bad.

Dan