Hovering over "Buy"... care to sanity check my thinking?!

[brumster]

So I originally joined up and posted the following thread in the welcome forum pretty much 2 years ago ...

http://www.mycncuk.com/threads/6914-...ick-hi-and-q-s

Since then I became overly cautious about diving in to CNC, and went for a 3D printer instead, and I must say I've really made (and continue to make) good use of it, making automotive brackets and so forth, and really feel like I've got my money's worth out of it. So my mind recently wandered back to my original plans for a home-made CNC so I started reading up again. And watching various YouTube videos, trying to find someone who had approached it how I'd like to approach it. Then I stumbled across this guy :-

https://www.youtube.com/user/featony

And *that* right there is exactly what I'd have envisaged as the perfect machine, and it also shows a build how I had figured it would have to be. And so it's confirmed for me that it's just too big a job to take on at the moment, I simply don't have that level of machinery around to make a decent enough job of it, and I see no point in doing it unless I'm going to do it properly.

Soooo... I'm thinking of a stop-gap learning exercise. Downgrade my expectations somewhat. And I'm finding it really hard to talk myself out of a cheap, crappy Chinese-made 6040 (I know, I hear the groans already). Thing is, even for their faults, I'm finding it hard to knock them in terms of outright value as a learning exercise. The 6040's have the 1605 ball screws, the high-speed (ish) motor for PCB work and by all accounts they'll do some soft aluminium as long as speed isn't a prime concern (it's not). I'll look to the VFD models with the better spindle, although won't fuss to much over the kw rating, they seem to vary anything from 0.8 to 2.2 on eBay.

Best I can make out, I can do some choice upgrades as time permits (or as they fail) :

• Replace wiring when it starts to fracture
• Fit a nice bed plate and level it myself
• Upgrade the electronics if/when they fail (sound like more "when")
• Swap the water pump pretty much straight away

Questions then...

1. Do they all come with limit switches now?
2. Various different representations of the control boxes on eBay; the 'newer' ones seem to be the black box design; is any of it really important or are they all equally as bad on the inside of that box?
3. Am I right in assuming the ballscrews are C7 grade so about the best that can be reasonably had at that size/price point?
4. I'm fairly au fair on the electronics/fabrication side of things, are there any cheap (open source/DIY) approaches to the motor drivers and control boards that I can look at to save money and get a higher quality solution? Would want something compatible with the main software, either LinuxCNC or EMC3/4.
5. Can't help but think while I'm at it move to EMC4 and USB
6. Any other choice upgrades/modifications I should consider? Thinking this is just a learning exercise for a few years, I'm happy to concede it won't deliver the quality level I originally intended in my welcome thread, but like I said, I'm just lowering my expectations and putting it down as experience.
7. Am I right in understanding the main limitation are these TBS drivers? Uprating them will allow the motors to be driven at higher V&A reliably? Are the TBS drivers just substandard/badly matched to the motors or something? It seems a common criticism... but then some get on fine with it "from the factory"?

I'm put off by the 3020 as I know they are cheaper but their use of trapezoidal screws concerns me for the accuracy/repeatability issues, particular with any PCB stuff I do, and also their slower, less powerful motor (again, my understand is the PCB milling will need some real high speed - I mean, ideally 60k+ but I can settle with 24k).

Am I being overly picky? Is the 3020 not significantly worse than the 6040 and I should just go super-cheap? Will the 3020 realistically do aluminium at *any* level, even if I accept the 6040 would only scratch at it :) ?

Then hopefully in a couple of years when I have more space and equipment (and knowledge!) I can contemplate doing something awesome like This Old Tony :)... but realistically, I just don't have the time right now :(

Thanks in advance for any thoughts/opinions. Happy to be shot down in flames ;)

edit: Thought - go 3020 and upgrade the ball screws to 1605-C7's? Worthwhile? Then uprate the spindle over time to a VFD?