Re: Seeking advice for cnc machine purchase
Breaking my responses in two as they were too long sorry Danny.
-- Stepper motors: So far I see one quote with 86BYG steppers, and one quote with 450A Steppers. Anyone have experience with these?
Generally for the big 6090's they'll have roughly 380 oz/in NEMA23's on X and Z, and a 380-420oz/in NEMA34 on the Y, for the big machines I found they seem to spec the steppers pretty well with the PSU and drivers. The 6040's are a little more loose. I've seen some that came with 420 oz/in steppers which given the crap controllers and PSU for them is just ludicrously bad. This is where the optimal PSU value determined by 32 x the square root of the inductance is critical. If your machine has 8mH steppers, it requires 90VDC to run optimally, but if it came with a 24VDC PSU and TB6560 based drivers, your in trouble!
-- Ball Screws: They all have them. (I believe they're better than ACME) Are some better than others?
This can vary greatly between sellers, not so much on 6090's but mainlyon 6040's. I've seen 6040's with unsupported round rails and ACME drives screws, utterly crap on a machine that size and build design. Drivescrews come in different grades, all the Chinese ones come with a generic grade pretty much across the board, and in practice will perform perfectly fine. The expense to go to a better grade would be really hard to justify in most cases. If a better grade drivescrew is required, then your really looking at the wrong machines I think.
-- Cables: Are they Shielded?
I don't think any of the Chinese sellers even get the idea of shielded cables other than a selling point, as they barely get the idea of proper earthing, so unless you get a really switched on seller (yeah right), you can expect non shielded cables, even if they were shielded, you could pretty much guarantee it would be purely cosmetic!
-- ??? Am I missing anything else important?
Not really, just hassle them heaps during the process to keep the pressure on you being happy as a customer!
It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!