Best way to attach Gantry to Frame

[Sterob]

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

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[Jim Dawson]

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

[cyclestart]

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

[Sterob]

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

[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.

[Sterob]

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.

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....

[cyclestart]

I'm pretty sure pippin88 is suggesting an alignment method similar to the one in this video.

[cyclestart]

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.

[machinedude]

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.