On May 7, 2008, at 7:24 PM, Jon Elson wrote: > Witek GB wrote: >> I am thinking of taking the plunge and buying a VMC maybe with an >> ATC. >> I plan on buying it for the iron and upgrading it to EMC. I have >> manual >> machine tools already so I know what to look for when I see a manual >> machine, but with CNC I really do not know much. What should I look >> for? Are there any resources on the Internet that show you what >> to look >> for when buying a used cnc? How can I determine if the ball >> screws are >> good or bad? Servos?... I will use this machine for hobby work and >> maybe some light production runs. Any help is appreciated > Servo motors are pretty tough. Really old encoders had light > bulbs in them. They can be retrofitted with infrared LEDs. > Many older machines had resolvers instead of encoders. (I'm > working on a lower-cost retrofit for those, but it may still be > cheaper to install US Digital encoders where they will fit.) I happen to like the Koyo's from Automation Direct but a lot of people use the USD's. > > Ball screws are fairly hard to evaluate in the field. You can > put a dial indicator on the table and see how far you can turn > the screw by hand to check backlash. The real problem comes when the ball screws are inaccessible. > > The general condition of the machine can be a useful guide. If > every nook and cranny is stuffed with chips, and layers of brown > sludge coats everything, you know the machine was run hard in > heavy production. That will take its toll. Gee, that describes my Mazak. Aluminum chips everywhere. If I had been thinking I would have had it steam cleaned before I got it into the shop. > > As for the ATC, the simpler it is, the easier it will be to get > EMC to control it. If it is a massively complicated hydraulic > monster with several changer arms, lots of position sensors, > etc. then it will be more complicated. Ray Henry did manage to > get the Mazak working at Roland's shop. That is a pretty > complex ATC. Remember that the tooling is a major expense on > these machines, a rack of NMTB 40 holders and collets is worth a > LOT more than most older machines.
I didn't (don't) know any better so I consider the Mazak ATC as pretty standard in complexity. Some of those on the horizontals must be simpler since they change tools in 2 sec or so. Indeed there is a major investment in 40 of 50 taper toolholders; which is a reason to acquire machines with one type of holder. Most of the machines will have CAT40 toolholders but of course you will see some CAT50's and a few NMTB's. BTW -- Witek GB .... where are you? > > Jon > > ---------------------------------------------------------------------- > --- > This SF.net email is sponsored by the 2008 JavaOne(SM) Conference > Don't miss this year's exciting event. There's still time to save > $100. > Use priority code J8TL2D2. > http://ad.doubleclick.net/clk;198757673;13503038;p?http:// > java.sun.com/javaone > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
