Z Gantry needs work

[jon-harper]

Currently the Z Gantry plates (PN022 and PN023) have four screws fastening them to the bed, but the Lead Screw Plates (PN027 and PN028) only have two. They're also connected by two M3 screws. This can be coordinated with fixing #7.

[jon-harper]

I have fixed the 4/2 M5 fastener issue, but other issues that should be addressed:

• The two halves should be more securely fastened than they are.
• The lead screw piece is too weak.
• The limit switch sensor should trigger by the lead screw (in front) to aid access to the thumbscrew.
• The linear rail can be moved up 25mm to bring the carriage closer to the lead screw nut and bed, lowering the center of gravity. This means moving up the carriage mounting points.