Steel frame cnc router design/build

[JAZZCNC]

I think steel is an excellent idea, so is a stick welder, but I would still like to take this opportunity to screw up your whole design at the last moment because that is what I do best
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When a weld cools it solidifies then shrinks. The shrinking bends everything out of shape with no possibility of correcting it. If you are a novice welder your welds are unlikely to be drop dead gorgeous and the effect is amplified.
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Meaning you end up with a framework that is wildly out of square, it fills half the workshop, is tricky to get it out the door and take it up the dump.
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If you are fiendishly clever you can try to pull everything square by welding in cross braces after the event and hold the thing in tension.
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If however you plan ahead and weld plates bearing bolt holes to your bars you have a chance to straighten things up after everything has cooled down. A round file can move a bolt hole, an angle grinder can square up a face, packing can be tack welded in place.

Don't listen to him he's just like to blow the froth of peoples coffee . . .

He's partly correct about heat and cooling, shrinking but if done correctly like I said short welds spread around it can be minimised enough to be fine. The wildly out of square comment just means he's been doing it wrong. .

The squareness of the frame isn't critical, yes it's got to be close but 1-3mm or so out won't hurt.! And if welded has mentioned it won't warp or twist anywhere near that amount.

It's the rails that matter and these MUST be square and parallel to each other and on the same plane.
To help your self with this on the Long axis, which I call X it pays not to weld the top rail but bolt it to flat plates. If there's any error then you can shim into plane and move parallel and square to each other very easily.

Then there are other little tricks for dealing with things like the top plates rails sit on arn't flat etc. Putting Epoxy putty between rail and plate creates a lovely surface and give enough time shim square etc and then when dry you have perfect surface and it's also helps dampen resonance.!!. . . . There I've give one of my tricks away. . Dam.

I do this all the time so believe me it's not difficult so don't let comments like "Victor" Robin "Meldrew" put you off welding because it's by far the Cheapest and strongest way to build a machine.

Edit: Better elaborate on the Epoxy comment.!! . . . You must put piece of cling film or thin plastic between top rail and putty other wise you'll stick the buggers together and never get them off. . . . . .Oh and it's not expensive. 125g packs for £2 and it goes fair way has your only spreading thin, 2-3 tubes will do full machine.