On 11/9/2015 4:55 PM, Andrew wrote: > 2015-11-09 20:16 GMT+02:00 Jon Elson <el...@pico-systems.com>: > >> On 11/09/2015 02:34 AM, Andrew wrote: >>>> there were hydraulic milling machines sold based on Moog hydraulics >>>> and Bridgeport iron. I assume those two companies could screw things >>>> up, but the world has moved on. To move a long distance takes a lot >>>> of power. Small movements with a lot of force behind them are really >>>> easy, that's why you see fatigue machines and other shorter stroke >>>> machines with hydraulic servo. >>>> >>>> AFAIK the problem of hydraulic actuators is low efficiency. There should >>> be a high pressure high rate pump to provide high velocity and force. But >>> when the actuator doesn't move it all goes via baypass just heating the >>> fluid. Probably adjustable pump could help but it gets more complicated >>> (just a guess). >>> >> Yes, some systems had fixed displacement pumps and >> regulating valves, others had variable-displacement pumps. >> Then, you have to provide cooling for the variable >> displacement pumps so it doesn't overheat when the machine >> is idling. In either case, the drive motor has to be quite >> huge, so there is plenty of energy wasted, and they make a >> HUGE amount of noise. So much that sound barriers have to >> be placed around the hydraulic power pack. >> >> Talking about hydraulics and CNC... > There's an old (~40 years) CNC lathe in our lab > https://www.dropbox.com/s/9cxnv0luduo11uf/SAM_2154.JPG?dl=0 > It has hydraulic boosters (amplifying valves) for the ballscrews > https://www.dropbox.com/s/nnkle9elu8lh90p/SAM_2157.JPG?dl=0 > A low-torque stepper motor rotates the valve, then the hydraulics rotates > the ballscrew. > There's a pretty large hydraulic power unit behind > https://www.dropbox.com/s/bqajpxwd8xs4dd7/SAM_2219.JPG?dl=0 > It has 7.5KW motor > https://www.dropbox.com/s/8ypf3d3yryb3dcq/SAM_2151.JPG?dl=0 > We turned the lathe on some time ago, the noise was very bad. > Its spindle gearbox with electromagnetic couplings also makes a lot of > noise at high speed. > The whole CNC with hydraulics was very unreliable, so these lathes had not > worked for a long time back then. > > Andrew > ------------------------------------------------------------------------------ > Presto, an open source distributed SQL query engine for big data, initially > developed by Facebook, enables you to easily query your data on Hadoop in a > more interactive manner. Teradata is also now providing full enterprise > support for Presto. Download a free open source copy now. > http://pubads.g.doubleclick.net/gampad/clk?id=250295911&iu=/4140 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users
The pump might have lost its prime. When they do they are very noisy. Swash plate pumps can be quiet compared to gear pumps. Once they build pressure and there is very little flow the noise is not bad at all. Heating is not bad at all. The old true servo valves were notorious for getting jammed up. If the oil is dirty they stick. Dave ------------------------------------------------------------------------------ Presto, an open source distributed SQL query engine for big data, initially developed by Facebook, enables you to easily query your data on Hadoop in a more interactive manner. Teradata is also now providing full enterprise support for Presto. Download a free open source copy now. http://pubads.g.doubleclick.net/gampad/clk?id=250295911&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
