I see a lot of the apparently simple things getting done wrong, and I would like to gather some opinions about the following:

1. How to fit a pinion to a shaft securely. I think the main issues here are that one cannot take any chance of allowing slip between shaft and gear, but the pinion needs to be replaced , so the process has to allow disassembly.
The methods I have seen include press-fitting, a reamed hole in the pinion with a grub-screw through the hub of the pinion that grips onto the shaft. What is the general consensus of the best way to do this.

2. How to create a separation between a welded steel structure which will certainly deform upon the welding cooling, and a precision linear guide that relies on a straight and flat interface surface to retain its' straightness.

3. How stiff does a gantry beam really need to be?
The loads on the gantry are:
- a torsional moment by the cutter reaction loads acting through a distance roughly related to the height of the gantry above the workpiece
- a side load on the beam that is equal to the cutter reaction load
- a downwards load equal to the weight of the carriage, z-axis and spindle in the case of a gantry style router.
- inertial side and "axial" loads caused by acceleration of the car, z-axis and spindle weight
I think it is as simple as this. How many did I forget?

4. Related to question 3, what are the typical loads and deflections allowed on the nose of the spindle/

I guess it has to be something like 300 N causing a deflection of max 0.5 mm or there-abouts. This is pure gut-feel. Any opinions?

These are some of the questions I am pondering as I consider the next bootstrap phase of my 4x8 foot router.