Rarius wrote:
> I think the problem of "racking" on the X axis is more of a worry. Although 
> not shown on the image I have decided to add a cable system like that used 
> on large draftsmans drawing boards to stop any rotational movement as the 
> carriage moves backwards and forwards along the X axis.
> 
> Rarius 

Yeah, that could be an issue. Since you've got two sliding rails and a 
third driving rail, your system is kinematically over constrained, so 
any racking between the two sides would put a lot more frictional load 
on the drive motor, possibly causing harm. This can be helped by doing 
what you said with extra cables, or another workaround is using thinner 
bearings spaced farther apart, instead of a single long sleeve bearing. 
That way any rotation can move the individual bearing races a little bit 
out of alignment, instead of putting a huge torque side load on each end 
of a long bearing.

How are you keeping z vertical? If x is the first motor, I'm slightly 
worried about it bending around y, especially if you have a large load 
on the cutter - it could bend against the long thin rails.

Another thing - the timing belt pulleys on the z axis aren't centered on 
the threaded rods?

-cshake

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