Hi all,
Would love some feedback and apologies up front for being wordy. Will intro the idea and then ask specific questions in the posts to come - but feel more than free to comment on anything



Intro
I've been looking to build a small mill/router for years but stuff got in the way. But now, it will be happening.
I am not an engineer nor machinist but I tend to research a fair bit - that said, I am not the best with deep dives into math so I do end up relying on anectodal "evidence" quite often.

As such, my design so far is a result of what I have picked up here and there and I am looking for feedback on it.

Goal
Goal is to machine aluminium and hold decent tolerances, perhaps +/- 0.025mm. There's a dream to cut titanium one day, but I know it may not be able to (stiffness, lack of flood coolant and wrong spindle) so we can put a pin in it for now, but if it could - even slowly, that would be a bonus.
I have a small product I want to prototype on this machine and make smaller batches of. Speed is not super important as if this takes off, I would outsource the machining anyways.

Budget
Budget is a semi-tight which might confuse you given some of the specs below like the C3 ballscrews but I can source quite a lot of this used and even a few things at very good deals. But think "budget, best bang for buck, but not opposed to spend a bit on good parts".

Granite, really?
I am chosing to have a base and gantry made from solid granite. I used to be based in China, have friends there and can get it to the Philippines where I live now with cheap freight despite it being heavy.

I know granite is not as stiff as steel but please don't fight me on this - this decision is set in stone;-). Why? Because it will be machined to 00 accuracy by a factory that makes surface plates and granite machine bases. They will also glue in all the screw inserts where I specify. So, it shouldn't need any secondary machining and with a granite precision angle I should be able to align all the motion parts myself. Bascially, I need to limit the risks of me effing this up and this is a shortcut to that.
And as has been pointed out - I owe a shout out to Piotr Fox and his surface plate build. Without it, I wouldn't have gone down this path

Size:
Travels
X: 230mm
Y: ~400mm
Z: ~ 230mm (under gantry clearance) but TBD...

Granite side wall and bottom thickness: 60mm

Alu parts (gantry and carriage parts) are 24mm thick

Moving Gantry, really?!
Yes... I have read a lot of accounts on how a moving table/fixed gantry machine would be stiffer, but I am willing to make a compromise here. I don't have a lot of space so the overall size has to be kept down. I also like the idea of the high side walls and plan on having end plates in acrylic to keep the worst of the chips contained. This wont be a high production machine so hopefully this approach might work - also for the same reason I am not too worried about the semi exposed motion parts.

As for the high side walls, the Z-clearance ends up quite generous at ~230mm right now. I will see if I can reduce this but I have a few fairly tall parts that I have in mind to machine. And if I need more stiffness, I guess I can put the vise on a stiff riser block to have the spindle operate at a height where it's assembly is stiffer?

Motion
Linear guides: 25mm
Ballscrews: 2005 (C5 minimum, possibly C3)
Closed loop servos, potentially servos...

Speaking of motion parts, most of this will be secondhand or NOS Japanese.
E.g. it seems like I can find some decently priced C3 ballscrews and have them modified to my specified length.

I was initially going to go with 2.3nm Leadshine closed loop steppers since I was afraid of tuning servos, but from various posts, it seems Deltas tuning is not that difficult and since I can get used B2s on the cheap, I might go with servos after all.

Spindle
For now, your regular Chinese 2.2kw, 24K rpm powered spindle.
Given that dream - with the pin in it - to machine a bit of Gr. 5 Titanium I thought about a 12K or 18K rpm spindle with a bit more torque at lower revs but it would be like sitting between two chairs, I think? For now, 24K Chinese spindle and then later if this machine has made money I can look into a proper servo driven low speed spindle.

Controller
Leaning towards UCCNC.
Was thinking of LinuxCNC for a long time, but too much tinkering in a field I know nothing about.
Masso, Acorn - too expensive.
Mach3/4 - not interested
Chinese standalone controller - I think for now, I would like to have a bigger screen with an easier way of setting up parameters, probing, etc.