Melbourne Andy CNC build 1220x810 work area

Oh well, in for a penny with this build........ Draft X-Axis frame design now ready for feedback please..... Here goes .......
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My CNC machine requirements are:
- Machine likely to mainly be used for machining wooden boards, but also plastics such as UHMWPE and PVC.
- Allow for some end-machining of board-edges and oversize-items and a future 4th-Axis.
- Need capability of engraving (flat) non-ferrous metals.
- Need capability of 2.5D machining of aluminium.
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Was initially thinking of 1220x1220 ..... but after becoming confuddled by what seems like thousands of threads have now opted for a working area of about 1220x810 for improved rigidity. Just hope this will be rigid enough for machining aluminium.
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This size results in X-Axis ball-screws of total length1420mm. . . . . inclusive of end-machining for BK bearings on both ends. . . .. . and inclusive of an extended tip for a pulley on the driven end. If my interpretation of "Metric Critical Speed" from www.nookindustries.com/EngineeringTool/Index is correct, then the 1610 x1400mm ball-screws have the following critical (whipping?) speeds which I hope more than covers my mostly hobby machine needs?
- If Fixity-B is the same as using BK12 + BF12 then a 1400mm x 16mm ball-screw has a critical speed of 09.8 m/min
- If Fixity-C is the same as using BK12 + BK12 then a 1400mm x 16mm ball-screw has a critical speed of 14.5 m/min
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Currently thinking of building the X-Axis frame as pictured mostly from 65x65x3 SHS. May yet upgrade the top rail supports to RHS.
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The X-Axis rails will have an overhang of about 100mm to cater for end-machining and allow for a future 4th-Axis roughly in the area coloured yellow.
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The split bed will be adjustable by nuts on threaded rod.
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Boards that are longer than 1220 can be machined in two passes by machining reference hole(s) on the first pass.
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Planning on using epoxy to level the X-Axis rails. Have initially sketched profiled linear guide rails but may well have to change X-Axis and Y-Axis to SBR25 supported round rail for budget reasons.
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Have yet to size the timing belt accurately, but it will be roughly of the order of 3000mm which will probably need to be custom made, so I'm hoping that such a long belt won't cause problems.
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Now need to consider the Y-Axis and Z-Axis in conjunction with affordable material availability in this neck of the woods. .. . .

looking good;)

Thanks deisel. I've cribbed much of the frame design that I liked from a picture I saved some time ago that JAZZCNC posted...... Btw I also have a copy of your fixed gantry beastie saved somewhere for a later date.
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But, I've just re-found Jazz's "little tea pot" picture posting and have noticed that with the picture he said "Do as I Say not what I Did"! Yikes! I hope my stupidity has not led me too far astray.
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So I have redrawn the adjustable bed to be less complicated as you suggested, and hopefully more rigid.

Looks good but is 100mm overhang enough for the 4th axis ?

Nah I say "Do as you like not what I say" . . Lol

Ok well I see one thing that needs changing.? Don't fasten the bed to sides by pulling on the sides. Make it so they Clamp like this.
Attachment 12146 Attachment 12145

This machine will have a 4th axis on the short end that over hangs, 150mm of overhang. The large overhang is to keep frame floor footprint down and saves wasted frame material.
Won't be using single motor belt drive as person who it's for wants to use large long material and the bar could be a problem. It will however use 20mm pitch screws with a 2:1 ratio to keep screw speeds down and reducing chances of whip while still maintaining same feeds as 10mm pitch. Will also get a bit extra torque.! Screw will also have BK Fixed end bearings at each end and be slight preloaded.