Joe90's BIG RAT Build.

[JAZZCNC]

Am I correct in thinking that

BK/BF12s are for 1605/1610 Ballscrews

and that

BK/BF15s are for 2005/2010 Ballscrews

Also, I don't see many builds using the other variety... the FK/FF type. Is that because the BK/BFs offer better performance or is it down to costs?

Yes BK12 = 16mm BK15=20mm

Regards the FF then they are a different fitment where they don't actually use a block that you bolt down. Instead, they bolt directly to something which is usually machined.
For instance, you would use them in situations like where you would machine a hole in the gantry sides and bolt the FF block thru the hole directly to the gantry side, you can gain a little extra travel this way. The downside is you have very little room for adjustment or error so require careful planning and accurate machining.

I use Motedis for my profile, they are cheaper than KJN, esp in regards to T-nuts, etc and usually quicker also a lot more accurate cutting.

Regards the motors and drives then I'd definitely suggest going with closed-loop but you need to pay careful attention to the Max voltage as a lot of the NEMA 23 sized kits use 50Vdc drives which means running around 45vdc which doesn't make them overly fast. Ideally, look for drives that allow 80-100Vdc or 50-70Ac.
AC drives are simpler and cheaper because you only need a transformer, where a DC requires a Transformer. Capacitors and Bridge rectifiers to make up the PSU.

I use Lichuan closed-loop systems on all my machines now.