The manual stresses that the Z-slider should not be mounted to the Stiffy but, instead, that we have to use the Gantry Block
In the event you have the Stiffy attached, ensure you do not use the holes in the Stiffy Block to attached the Z-Slider.
Why is that so? I have just upgraded my original Woodworker with a Z-20 and it would seem to me that the slider has enough travel to be useful even when attached to the Stiffy. I know some mount riser blocks to increase the Z travel… but it seems that the Stiffy would do an excellent job.
Is there a risk of breakage or is it just that the original slider did not have enough travel? If anyone knows…
I have the same plan as you, but on a different setup.
I started with an original X35 WW with 3rd rail, and now have the same but the X50 version.
The 3rd rail block does not line up with the gantry blocks to form one mounting surface, and there are no mounting holes - unlike the X35.
I am designing a new Z assembly that will use linear rails/guides, and plan to have a mounting plate that will attach to the x gantry blocks at the front, and the 3rd rail block at the top. It always seemed a missed opportunity not to have a Z assembly connected to all 3 blocks.
To your question, the only thing I can think of (besides Z height range which will depend on use cases) is the challenge of alignment of three rails/blocks vs two. The 3rd X50 rail is not attached with many fasteners, and the machining and attachment is not particularly ‘precision’ (in my opinion) relative to the x gantry. So, if the alignment of the 3 rails is off across the full range of movement then that may put undue wear/strain on the linear motion components.