On Saturday 09 February 2008 13:05, Kirk Wallace wrote: > How do they get the work piece to move in the Z direction while turning? > The work piece must be clamped at all times in order to maintain the > part index. The bar stock must have a fairly accurate OD. How accurate > can the parts be if there is slop between the bar stock to allow for a > slip fit and OD variation? How long of a bar can they run? > Kirk Wallace (California, USA
the swiss types have a sliding headstock ,like a twin of that pickoff spindle in the vid they usually push the material thru a guide bushing like a steady rest on an engine lathe in this video they've taken out the guide bushing and are running straight from the headstock collet http://video.google.com/videoplay?docid=1855769711153176498 with the guide bushing supporting the stock just behind the cut you can run long parts without having them flex away from the tools but you often have to take the full cut in one shot because you cant draw it back into the bushing very far after its been turned its best to use centerless ground stock but you can get away with cold rolled most of the time and the parts are very accurate ,the bushing is built like a collet and can be adjusted to a light drag on the stock so there's really no slop there with a rotating bushing you can draw it down to almost grip the stock but the runnout from the bearings will show up on the workpiece ,for best concentricity you'd use a stationary bushing with constant oil flow so it acts as a Hydrodynamic bearing ,its more accurate but limits your speed the live tools can be gear or timing belt driven and some like the polygon head can be synchronized to the spindle RPM but they don't index it just looks that way because they stop so fast ,we've also used air spindles on a couple jobs t,he live tools are fairly light duty but even then its quicker to drop the part off complete than to have to do 2nd operations on them you usually run twelve foot bars on these and because it has to reach thru the bushing you end up with fairly long bar ends (about 6 or 8") if you push the bar out to a stop you can open the collet and drop back for another bite and run parts longer than the Z-axis travel of the machine ,I've heard of one with a bar gripper just behind the bushing that would act like a stop ,you could cut a taper the full length of the bar with that one and they will set you back a fair chunk of change ,you're looking at 1/4 to 1/2 mil for a new machine and accessories ,but with a magazine bar loader you can run them 24/7 to keep up with the payments oh yea another little quirk is that the swiss lathes are left handed,standing at the control the headstock will be on your right Brian ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
