Hi All, and thanks for any advice anyone is able to provide, its greatly appreciated.

We've currently got a project where we are building a massive 2.5M x 4M bed machine with a multi function bridge/gantry.
Its primary use is for a nailgun, for nailing in a pattern but while we are building it it might as well be able to machine as well.

Anyone who isnt sure what we mean just google 'MBA Mobi one' or 'weinmann wms 100' but we intend ours to be much more compact as space is at a premium.

We all ready have the massive overkill NSK 55 profile rails and the bed/frame side of things is not a problem. What we cant decide on is the design for the gantry itself...

so far we have come up with the following...

1) use a large hollow section with the rails tapped into it but would a piece of flat bar be needed under to increase the thickness to get a good tap?

2) use a large c section with the rails bolted through?

3) angle welded flush to face of a hollow section to allow bolting through?

4) smaller hollow welded to produce the gantry?

any ideas and experience of any of these??

I'm assuming that one rail on the front face and one on the top face of the gantry would provide a better design or does it not really matter?

We also still haven't decided on the drive side for it either, whether rack is the way to go or rotating ballscrew?

thanks in advance

Tony