That does sound like a lot of work when a simple acme screw and plain bearing slides do the trick.
http://gnipsel.com/shop/plasma/z-axis-02.xhtml John On 11/12/2012 5:32 AM, Les Newell wrote: > If you want to go with the auxiliary slide idea you can often pick up > short linear slides off eBay for peanuts. Bolt on your torch, add a > switch and the job is done. I have some nice 100mm long THK rails here > that I bought for this purpose. > > I have been thinking about this for some time and a while back I came up > with a very different design to all of the others I have seen. First of > all, you don't need or want a ball screw on Z. Z doesn't need to be > hugely accurate. It needs reasonable resolution and it needs to be dirt > resistant. Plasma generates a lot of very fine abrasive dust that gets > everywhere and will wreck ball screws fairly quickly. My plan is to use > a simple winch. Think of a drum with a coarse thread machined into it. > Wind some flexible wire or heat resistant cord on the drum and control > it with a stepper or servo. This is simple, dirt tolerant and provides > good enough accuracy. Run the wire over a pulley at the top of the Z > axis to lift the torch. The weight of the torch and slide should provide > enough tension. > > For touch sensing, mount the pulley on a spring loaded arm with a hinge > at one end and a switch at the other. As the weight comes off the cord > the pulley will lift and trip the switch. Alternatively you can have a > fixed pulley and a separate spring loaded pulley and switch to measure > the cord tension. > > The main problem I can see with this setup is the possibility of the > cord coming off the drum. This can happen if the cord goes slack. There > are a few ways to get around this. One is to add some guides so there > isn't room for the cord to lift out of the grooves. Another is to stop > the machine if the touch sensing switch trips and you aren't seeking the > top of the work. This is worth doing no matter what touch off mechanism > you use. > > I have used the grooved drum setup for position measurement and have had > very few problems with the cord coming off. After initial calibration > they maintained surprisingly good accuaracy. > >> I dont think your idea is a good practical idee for a production >> machine. The torch does touch off thousands of times and the loose nuts >> will wear out in no time. There is nothing wrong with a well designed >> floating head and in my opinion it is the best possible pactise to date. > I can't see why the nut would wear. There is very little load on it when > it moves on the pins. Instead of bolts you may want to use hardened pins > as they can be made a better fit and will wear less. > > Les > > ------------------------------------------------------------------------------ > Everyone hates slow websites. So do we. > Make your web apps faster with AppDynamics > Download AppDynamics Lite for free today: > http://p.sf.net/sfu/appdyn_d2d_nov > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_nov _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
