Joe90's BIG RAT Build.

[Neale]

My approach to this problem was to use 20mm rails, and 20mm Ecocast plate. This gave enough depth of material to be able to pocket the plates for clearance around the nut holder. The important point here is that the pocketing is for clearance and is not super-critical in terms of dimension. This means that you can use a woodworking router to do the job. I actually used my vertical mill, but if you search the forum for (from memory) Joeharris's posts he talks about how he used a conventional handheld router successfully to machine aluminium. Might be worth a look and a few back-of-emvelope sketches. I know that I spent a long time on the details in this area; apart from anything else you have to be able to assemble the Z axis and I ended up doing things like drilling access holes in the moving plate to be able to get to a few allen bolts going into the fixed plate. All good fun!

[JAZZCNC]

My approach to this problem was to use 20mm rails, and 20mm Ecocast plate. This gave enough depth of material to be able to pocket the plates for clearance around the nut holder. The important point here is that the pocketing is for clearance and is not super-critical in terms of dimension.

This is the easist and best way to build a Z axis. Packing rails off or bearings off is a fiddly bodge. 15mm rails while more than strong enough are fiddly things and make it awkward.
You could go with 25mm rails and get away with no machining but then it gets tight with space and really requires a wider Z axis, plus there's more mass to deal with.

Hand machining isn't difficult provided your comfortable using a large router. I did several of the parts for my first machine this way and was the one who talked Joe into giving it a go, however Joe cut far more parts than I did using this method and made a very nice job of it so I'd advise anyone thinking to do this to go check out how he did it.!