Most of these 6040 CNC variations are made in the same factory and sold by many different companies. They are made in China and from what I have seen they are assembled with the cheapest parts available at the time of manufacture to keep the cost down. They use several different motion cards depending on what is the cheapest at the time. The big problem I have found is these machines are sent with instructions for configuring the system with the wrong motion cards so they won't work if you can't get them to provide the correct drivers for the card that they used for the unit. Some companies do provide the correct documentation and are willing to help resolve problems but others will never answer email or provide any help after they receive your payment.
I think the important thing would be to buy from places that protect you in the event that the seller will not work with you to make sure it is running. That way you don't have the headaches of getting the unit running or have to pay someone to do it for you, or worse, never get it running and wasting that money.
This same problem exists with many of the control cards when bought separately so I think that adds to or helps create the problem. Some of these companies also provide CDs with several different drivers and many times pirated Mach3 software copies registered to Chinese names. I don't recommend using the pirated software and make sure you don't accidentally contaminate your Mach 3 by installing it per their instructions for configuration.
The units I have worked on are basic hobby level machines with limited feed rates and most will have a 1.5kw water cooled spindle. If they don't have the spindle I recommend using a trim router and not a 2.25hp full size router to help limit flex from too much weight.
Personaly I would not recommend buying one but that is just my own opinion from working on them.
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