Tips on what to look out for when buying a used CNC mill

Hi all,
I'll be purchasing a used CNC bed mill in the near future. Probably one with Anilam conversational control. I'm looking at ones for £5000+
Any hints and tips about what to look for when buying a used CNC bed mill?
Apart from running the spindle low to high for sound I can't think of anything?
Thanks

Get them to program and cut a square boss on a piece of ally and check it is square and also dimensionally accurate.

Tony

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.

Thank you very much for your help guys. I shall print this page out for reference!

Michael and Nigel - after what you have both said about the in depth checks I think i'm going to buy from a reputable dealer and not privately. At least I may get some kind of warrenty then. I was looking on ebay and there was a Semco with anilam which I am trained up on but as it's private and I'm not an inspection expert I'll avoid it. It was a bed mill going for 5k.

Nigel, I have no experience with Heidenhain but if its conversational I should be ok and I'm a fast learner.

Have either of you guys used Hurco control? And any dealers in the south east you would recommend?

Thanks guys, much appreciated.

I have no experience with Heidenhain but if its conversational I should be ok and I'm a fast learner.

Have either of you guys used Hurco control? And any dealers in the south east you would recommend?

Heidenhain pioneered the conversational approach - programming & operation is very straightforward. The adoption of the early models as standard equipment on Bridegport Interacts helped get them widely established here - the current "high end" controls are 5 axis & optimised for high speed machining (fast block processing times).

I have no experience of Hurco controls - though one of my old customers had one & was very complimentary about it. I used to work for a CNC machine tool rebuild & retrofit company & my experience is with the controls we used to fit - Heidenhain, a (very) few Bosch, GE Fanuc, Osai, Siemens and 1 Fagor installation. As Hurco use an "in house" control that does not appear to be made available for third party installation, I did not get the opportunity to play with one. Likewise, I have no experience of Semco machines, though a quick look at their website shows the current bedmills as being "Ajax" branded. Ajax CNC milling machines used to be Spanish (Lagun) when the company was based in Stockport. I am not sure where the current owners of Ajax source their machines, but the Laguns were well made & sturdy machines.

As I live "Up North", I have no experience of Southern based dealers. My current employer largely stays clear of dealers, buying mainly from auctions. I sort them out, install them & keep them running (easier said than done sometimes, as the company is purely a graphite machining operation). The previous employer was, in the later years, a dealer of sorts - he would buy machines & rebuild/rewire/retrofit for stock to sell against new machines when rebuild or retrofit orders were slack. He specialised in the larger end - the last few years were mainly 48" and larger vertical borers, though we also did a few Butler Elgamill travelling column milling machines & similar. The size of machine shown on the Semco site was not cost-effective to rebuild or retrofit from the mid-90s, as the price of a new Far Eastern machine was less than the cost of a rebuild or retrofit (the volume MTBs were paying less for a complete package of control, axis & spindle drives, axis & spindle motors and cables than we could buy the control alone for).

I have retrofitted a Heidenhain TNC320 onto a Cincinnati Sabre 2000 recently & have a Heidenhain Manual Plus turning control under my desk waiting to go onto a Gildemeister NEF1020 lathe. Both these machines are only worth the cost of retrofitting because of their capacity. Both were bought at auctions for relatively low prices & will stand at less than a normal dealer price after retrofitting. In both cases, the cost of the retrofit hardware (not taking my time into account) was 2-3 times your initially stated budget ! The Sabre really had to have the control changed,as the original Acramatic 850 proved difficult to get going & the trouble with an older "oddball" control is that you can quickly run up a very large bill with the few specialists capable of looking after them. Hence the decision soon after installing the machine to bite the bullet & replace the 850 rather than pay to get it sorted.

Good luck with getting much of a warranty - most older machines will not come with much beyond having it demonstrated as working when installed.

Hi There

Heidenhein is very easy to learn. It is like driving a sports car while G code is more like plodding along in a muddy field.

I taught myself from the manual in a few days.

I snapped one drill in the first week, that was all.

Hurco are ok, some have a sort of conversational control which I think was based on G code.

regards David