Best way to attach Gantry to Frame

If I was to build a steel framed Moving table CNC Router, and I wanted to get faces of the x and y axis ,where the Rails will be attached, machined flat and in the same plane, I can think of 3 ways to do it (are there any more? )

1.Weld the frames up separately, get them machined ,and then weld the Gantry to the main frame. ( May get distortion caused by the last welds?)
2. Weld the frames up separately and design them so they can be bolted together after machining. ( Would bolting the frames together comprimise the rigdity of the whole machine and become the weak link?)
3. Weld the complete machine and try to get the faces machined. ( I doubt this is possible ...too awkward.)

Your thoughts Gentlemen, thanks.

Steve

All of the moving table machines that I have seen have the gantry bolted to the lower frame. This allows alignment adjustment after assembly.

#2 seems most practical and #3 least practical.
The attached Multicam photos show.... something.... they are the highest resolution I could find.
Attachment 448092Attachment 448094

Thanks guys.
I guess it allows 'some' disassembly of the machine , if it needs to be moved, as well.

You can avoid machining the joints entirely using a "replicated joint". Align using series of screws in opposition (some acting as jack screws, others holding down) then inject an epoxy.

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Originally Posted by pippin88

You can avoid machining the joints entirely using a "replicated joint". Align using series of screws in opposition (some acting as jack screws, others holding down) then inject an epoxy.

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Not sure what you mean.Are you talking about the junction of the Gantry with the Frame?
Epoxy is a way of maintaining alignment of the gantry?
Googling 'replicated Joint' didn't give me any clues....:confused:

I'm pretty sure pippin88 is suggesting an alignment method similar to the one in this video.
https://www.youtube.com/watch?v=U7Qs-J2swIc

Back to clarify that I posted the video as a practical example of epoxy in use. The base to upright (column) alignment on a c-frame mill is more critical than on a gantry type machine which has other possible points of adjustment.
I have no experience with the Diamant DWH used in the video so can't speak to availability or price. What I have used is common JB Weld steel filled epoxy to level rails. It claims "0% shrinkage" and high strength in compression. JB Weld isn't advertised as a product for precision applications and possibly it's unsuitable but it seems to be working. JB Weld can also be machined. Hmm, this is starting to read like a testimonial :) it's not meant to be.

that's a very important aspect of setting the machine properly if you want things to be accurate. when the head is not trammed to the table you get a mismatch on the edges when you surface anything. the miss match comes from the tapper on the Z axis plane. you can surface the table top to make it flat in one plane but still get the mismatch if the Z plane is not square the the table. the 4 points of a large circle with an indicator get the side to side and front to back aspect of the Z plane. the larger the area you tram the better because the Z plane is more exaggerated over a larger area. so if things are out you may notice that with a small cutter surface mismatch might not be that bad but if you use a large diameter cutter things tend to look worse. this would be why you notice it with large cutters.