Let The Fun Begain, New build on the Table.

[Jonathan]

Ok better explain myself in case I'm wrong.

I thought your first explanation was good, but the latest one is even clearer. I agree with the 39-51um figure and as you say it's likely to be more. Any compromise like this will reduce the stiffness of each element. You can analyse the stiffness of the overall machine as springs in parallel, so if you reduce one a very small amount it's not likely to make a tangible difference, however if one is reduced substantially such that the stiffness is lower than other elements, then that will dominate the system, causing the overall stiffness to be low. This means compromising one part can waste money you've spent on other quality (stiffer) parts. An extreme example would be using profile rails on two axes and unsupported rails on the other. In that instance changing the profile rails to supported rails isn't likely to make a difference, since the weak point would still be the unsupported rails. Similarly, 'making a box to encompass the support rails' wont make much difference, since that part of the assembly is already at least an order of magnitude stiffer than other parts.

You can get the ballnut in a more optimal position with the current design - it doesn't have to go behind to do that. Similarly the current design could easily have a 'box to encompass the supporting rail' added.

Switching would save a lot of hassle having to sort extras like seals and way covers etc.

Just stick a 15mm shaft seals, like these, either side of the ballnut and the swarf is wiped off easily. They're working well for me and not showing signs of wear, although admittedly I've not been using them for long.