Aluminium Profile Type Router - Initial questions

[AndyUK]

Reading some of the new threads I've been re-thinking and slightly concerned that the accuracy I'm building too could result in inaccurate final results.
As this is all "by hand" and printing 1:1 scaling, drill holes are perhaps up to 1mm out, I'm using a digital caliper and angle measuring device during the build, but check as much as possible
There is some slight adjustment by the hole sizing on everything - how much can the software make up for sub mm "corrections"
Maybe overthinking it - but also don't want to end up with something not accurate after all the effort.
As I haven't owned a CNC machine before I don't know what accuracy I'd like, but for example if I could produce something like the Aztec calendar I'd be happy..

First off, looks like some great progress in the photos, well done!

Regards the by hand - quite a few of us have used this method to good results. Yes, sometimes you cock it up, but just be slow and methodical double checking measurements.

No idea of your experience so lets ensure we hit all bases; make sure to centre punch well (optical if possible - the press type I also like), and let the drill bit align to that punch mark (if you clamp too tightly aligned slightly off, the bit won't happily sit in the punch crater). Use the drill press as much as possible (but check its square to the plate in both directions). If you're not using printouts, use marking dye. Set your digital calipers to the value from a reference surface, lock them off, then use them to scribe the line. When using a steel rule, never use the end for final marking (its a bit variable), always align to markings on both sides (e.g. to measure 10cm I'd align the 1cm mark and the 11cm.) - Now check using the end on the first mark!

If you come to fit components together and the holes are a bit out, you can always identify troublesome ones and widen only those. An M5 clearance hole already gives you 0.5mm of wiggle room, a 6mm hole isn't going to be the end of the world. Worst case is you have to make it again (oh no!) or remake it using the CNC later.

Regards accuracy - mostly to do with how you align the linear rails and screws. Use a dial gauge and get everything running smoothly and true to a reference surface. In your case this is mostly on ali extrusion or cast ali plate, so the height of the rail shouldn't be a massive issue - shim slightly if required, and you'll have plenty of left-right wiggle on the extrusion T slot. Your main problem will be aligning the two sides of the long axis so the rails sit at the same height. You won't go too far wrong if things move smoothly. Avoid software corrections as much as possible - the main one is the steps-per-unit, which shouldn't be too far from the calculated value (if it is very different, somethings probably lose).