CNC Router V1.0 (For Cutting Multiple Materials)

[biketrialsdave]

OK, so I warned of a whole heap of questions when I first started this project. Here are a few of the ones at the top of my list... If anyone would be kind enough to answer just one that would be very much appreciated! I hope they make sense...

1. Should I rebate/slot the aluminium plate where the aluminium extrusion butts up against it? Would there be anything to benefit alignment strength wise? I have done this with the extrusion piece connecting the gantry sides at the bottom but was thinking of the main X and Y extrusions.
2. This is a general tolerance question. Should I perform a worst-case tolerance stack-up when calculating tolerances for holes etc? A particular question I have regarding this is the diameter of the bolt holes. I want a close-fit to aid with alignment. EDIT: So for example an M8 bolt, what clearance should I include and what is a realistic tolerance if I have the aluminium plate machined manually or on a CNC mill? I'm going to use the ANSI dimensions for hole clearances etc. Should I go for close or normal fit for bolt clearance?
3. Following on from the above question...Another particular example of the tolerance question is where the Hiwin carriages are recessed into the gantry 'uprights'. The carriage blocks are 44mm high (I cannot see a tolerance in the datasheet...). Lets assume this tolerance is +/-0.1mm. Should I specify the slot in the upright to be 44.2mm +/-0.1mm? This would ensure the part would definitely fit, however if the carriage was only 39.9mm then this fit may not be tight?
4. Would my design benefit from an Aluminium plate across the back of the two extrusions on the X axis? If so, should I mount this to the two gantry 'uprights' as well as the extrusions? Would 10mm thickness suffice?
5. In my current design I have the Y axis hiwin carriages mounted to the lower portion of the 80x80 extrusion profiles. Would there be much difference/benefit in mounting these to the upper portion?
6. How do you determine how heigh to have your Z axis? What I mean by this is do you design around a typical flute length and add some? Should the Z axis be able to go through the bed?

Cheers,

Dave