Why with an Anilam control ? As Anilam are no longer developing or manufacturing (bought out by Heidenhain IIRC) long term support may be an issue, particularly as Anilam were never what could be called mainstream controls over here.
For a conversational control on an industrial mill, I would go for a recent-ish Heidenhain control – the older TNC145, 150, 151, 155, 351& 355 controls are getting more awkward/expensive to fix though, so don't pay a premium for those models. For universal "appeal" – go Fanuc. For seriously expensive spares & "different for the sake of it" – go Siemens
What to check for ? Depends how much time you have & how much the vendor wants to let you do. I would try to pull all the slideway covers back to check for scoring on the ways & that the lube system is working. On older machines with plain bearing slides it is not unheard of for the slideway liner (if fitted) to come loose (if there is what looks like a thin piece of plastic coming out from under the slide – light green or beige usually – that would be the anti-friction liner. Expensive fix !).
Jog all axes at rapid traverse & listen for untoward noises – grumbles, rumbles or speed-dependant whines could suggest ballscrew or support bearing problems (or linear bearing problems if the machine does not have plain bearing slides). Expensive fix ! The axes should accelerate & deccelerate smoothly and not generate servo alarm messages on the control. Be aware that many machines operate at reduced traverse speeds in manual modes – get the vendor to demonstrate the full traverse rates in auto modes. Jog the axes in alternate directions (full forwards directly to full reverse) & listen for knocks that could indicate excessive backlash in the drive system. To properly check for backlash requires a dial gauge.
Try to get the vendor to machine a "NASA" test piece – a cylinder above a square diamond above a square. The square & square diamond should measure the same across the corners & across the flats – if not there could be geometric errors. Mount a dial gauge in the spindle, position over the centre of the cylinder & "tram" around the cylinder periphery. The cylinder should show round, not oval (geometry or servo setup error) without steps or marks at the 3,6,9 & 12'clock positions (backlash or loose gibs).
The spindle should run up smoothly to full speed (forwards & reverse) without untoward noises – though backlash in the gears can show up as a a rattle under light loading that reduces under machining load. Check the spindle taper for scoring & excessive wear (Blue up a good toolholder, insert in taper, release & check for even marking in the socket). Do a tramel check to the table – vertical machining centres usually wear the head (Z axis) so that the spindle is out in the Y axis direction. Expensive fix !
If it has an ATC, have it demonstrated & check all pockets for damaged retention clips.
Try to talk to an operator who has run the machine (or management where it was last operated) to find out if he has had any issues with it – more difficult if it is at a dealer or auction, but I have managed to track down original owners of some of our machines in the past & no one has told me to "go away" (or words to that effect ! ). Most have been very helpful.
Check that all the documentation & data back-ups are present – this can be almost impossible (MTB gone out of business) or serioulsy expensive (if they are still trading, or have an ex-agent still trading) to get hold of. Loose the parameters or PLC program due to a control failure or back-up battery failure with no data back-ups & no documentation – expensive fix !
If you are not sure what to look for – try to take along someone who does. A thorough check-out is not a two minuit job, though.
HTH
Nigel B.