OK getting to grips with Fusion360. So just to show I have been listening (hopefully), here are some drawings showing the critical clearance and overall dimensions of my Z axis. A little more adjusting probably needed, as I am trying to get the standard components into as tight a practical design as I can manage. Have I over done it? A lot of faff to reinvent the wheel I suspect but a warm up for the more challenging X axis!

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Still feeling like I am panning for gold on this site! Found some great photos of a XZ assembly in Joe's 1000x600x200 Build Log. Thanks devmonkey.

Also appreciate NordicCNCs build log - Whilst he is going for something much bigger and metal cutting, the mantra of keeping part count down and design simple chimes with what I want to do.

A few design choices still bug me:

Gantry: I absolutely get the L design and advantage of 45x90 extrusion for bolting the BK12 directly to. However I am not wild about the complexity this brings to the X /Z assembly. A 'C' shaped gantry where the screw can run between the rails would allow a simpler plate like. A 'C' from 45x90 (ie 180x90) seems overkill....but then if the BK/F 12 bearings (or FK/FL) are mounted to the gantry end plates then there is more flexibility in positioning ball screw and maybe using 3 slightly lighter extrusions 30x60 (ie 60x120 C gantry). Sure others inc Jazz have been here before, am I wrong to fear this?

Stepper Mounting: Direct drive fits with my minimal parts concept, but if I go for the more powerful Lichuan closed loop steppers they get quite long at 125mm! I liked how the UKCNC kit accommodated the direct drive steppers within the frame, but they are much smaller motors. So if 1:1 pulleys and HTD5 belt are only going to add £10-15 per axis and allow tighter envelope, then maybe. Are there other performance benefits, like acting as mechanical fuse?

Spindles: For wood, I'm not sure I need 2.2KW and ER20. I think 1.5KW and ER16 would be plenty as that would allow up to 10mm (covering common 1/4" and 8mm tooling). I can only imagine wanting to use 1/2" tooling to get 2" depth of cut or run a big surfacing bit. Then again I can see the 2.2KW water cooled spindles cost not that much more. Given the Shapeoko and Openbuilds crowd seem enthusiastic about adding 2.2KW beast to their less robust machines , what am I missing, or is it all for Aluminium cutting?