Help on a couple of "niggles" with my machine.

[Washout]

Update guys after getting some time to dismantle my Z and Y axis (Z needed some maintenance anyway).
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Dean, you were spot on - the Y axis ballscrew locking nut must have slipped a little bit and was allowing a bit of movement - I've had this problem before and thought I had cured it by using a beefier set screw, so I may end up drilling out the copper/brass pad in the locking nut and trying a direct clamp from the set screw this time (with Loctite).
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Of more concern is the Y axis chatter, which was probably only partially the fault of the ballscrew, as I have examined the bearings for lateral play (see photos) and I am able to "roll" the z-axis in the direction of the arrows (shown in red) and I can see about 0.5mm of "light" between the bearings and the rail. I know from other threads that round rail and bearings are prone to wear and probably in exactly this sort of manner.
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So I am thinking to fix it temporarily I'll loosen and raise the main 120x60mm cross beam to take some of the slack out (shown in green), but also look at replacing with profile rails and bearings (20mm possibly) - I'll either use Chai if he does these, or Zapp/Gary for convenience, if I can work out which bearing blocks I should go with and whether the whole assembly will fit in the same space? Hopefully they will fit in place of the existing rail/bearing units, but the top and bottom carriage extrusions will likely need replacing with ali plate custom cut affairs.
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Question - I take it the profile rail/bearings are an order of magnitude "stiffer"?
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I also have the option for the top bearings to make the carriage plate wider by ~60mm each side, which I am thinking will be even more stable as the bearings will be further apart? (shown in blue)
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As always opinions/advice welcome.
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Cheers
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Chris