Build continues and upgrades plus review.

[Jonathan]

Looking for input on ... raising the Z axis while keeping the rigidity up (if not increasing it). I am looking at either Alli' plate or extrusions and would like input there on the Y/Z axis unit (going to raising to 100-125 mm travel to allow the addition of an A-axis to the unit [already have the unit]).

Just make it as strong as you can. Extrusion is great if you can afford it. Plate is the worst solution in terms of bending for the gantry sides. Aluminum or steel channel or box section will be much stronger with forces parellel to the Y axis for the same mass. Irving posted an excellent spreadsheet about it somewhere...

I would be inclined to increase the distance between the bearings on the X axis. This will of course loose travel but it may be neccarcy to keep it rigid.

You could consider just simply raising the Y/Z axis to fit the A axis and leaving the Z axis with the same travel. That way you will only have the bending of taller gantry sides to worry about. When you don't want to use the A axis drop it down again. The slots in the aluminium extrusion make this easy to do and you could put a block of aluminum on either gantry side at the current height to locate the gantry so you don't have to get it level every time.

I have been looking at Zap and a few others and would like in put on the best method for setting up the bearings for the ballscrews and if it would be wise/possible to upgrade to 20mm ballscrew from the 16mm trapezoid screw that is currently there (this is on the X axis, on the Y and Z I plan to upgrade to increase rigidity a bit).

The eBay seller linearmotionbearings2008 is much much cheaper than Zap. They will cut the screws to length and machine them. I've ordered a few times from them and not had any problems.

The diameter of the ballscrew required depends on the length, and end fixity. I would put a double row angular contact bearing (or a pair of single row) at one end and a standard deep groove bearing at the other. The best way is to have angular contact bearings at both ends, however the critical speed of a 16mm screw, 400mm long (just guessing the size, correct me if I'm wrong) with the above bearings is around 10,000rpm - so plenty! I'm using a 550mm (ish) 16mm ballscrew on my Z-axis and it happily went at 10,000mm/min - it's limited by the motor torque.

Since the critical speed for a 16mm ballscrew is so high there's not really much point using a 20mm screw. You're not going to exceed the load ratings of the 16mm either. Also if you had a 20mm screw the inertia is much greater (the effect is proportional to the diameter of the screw to the power 4), so your acceleration will suffer. The same is true with changing from 12mm to 16mm screws, however ballscrews are much more efficient than trapezoidal screws so you'll end up fine. Thinking about it it's not really an issue since the screws you have currently are 3mm pitch (I think?), which will have to turn faster than a 5mm pitch ballscrew ... so etc... (I think I've written enough!)