I've explored the limits of the current MK3 machine and it's time for an upgrade ! I want to cut aluminium more successfully with a better surface finish.

Here is the design so far, generally happy with it but tweaking minor things here and there:
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Z axis
Box-Z design clamping the spindle all round. 15mm 4off profile rails and 8 carriages. Went for the single Z ballscrew in the end as couldn't get a twin ballscrew design to fit and give reasonable travel etc.
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This is how the spindle clamps, but still keeps the rails aligned:
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Y axis
Twin ballscrew driven with box surrounding Z axis. All joints overlapped such that pre-load can be set on rails before tightening. Has 20mm profile rails on 5mm epoxy.
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X axis
Twin beam gantry design using 60x100x5mm RHS steel sections. This sits on 16mm open bearings which are on 16mm simply supported rails. Cannot get finance approval for 1000mm profile rails so am re-using existing parts. I'm going to use 6 open bearings per side to get the most stiffness out of it. When the time comes there is only minimal work to adapt to profile rail.

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The gantry is driven by twin ballscrews, and I tried lots of layouts to get them syncronised before getting to this one. Still not 100% decided - this one has 5M HTD pulleys 31.8mm dia with 15mm wide belts. To get the link across means bolting 2 pulleys back to back. Also thinking about a single 25mm wide pulley with 9mm belts shared between the stepper and the link across (2 belts per pulley), but need to read up about 9mm vs 15mm belt strength etc.

The energy chains are split down each side. LH side is for spindle power cable, RH side is for stepper power, home/limits, auxillaries, and water cooling pipes. Now that the control box is 24V logic for limits, (homes still WIP), and all cables are shielded I'm hoping that running them together in the RH side will be OK.

Not decided on water cooling arrangement, got several options which I'll post when I finally decide. The current radiator & fan is quite bulky and 'sticks out' where ever I put it.