On Fri, Jun 05, 2009 at 09:50:44AM -0700, Kirk Wallace wrote: > I've had a hard time finding a good vendor for ball screws. I orI tried > Hiwin which did not turn out as well as I'd like. > http://www.wallacecompany.com/machine_shop/bridgeport/ > (See bottom of page)
Aargh! That takes a lot of the fun out of the exercise, at least for a time. :-( Many thanks for the heads-up for the rest of us. I scanned the Hiwin ballscrew catalogue, after reading Dave's post, and was concerned by the graph on page 9, showing service life cut to a tenth by an assembly inclination of 2 x 10^-4 "?cc". Whatever the illegible unit, it suggests that installation without laser guided servo-actuated jigs in clean-room conditions dooms their product to uselessness in a week. Mind you, if it's that bad, then we just have to couple to the axis with a zero-backlash ball-joint, I figure. I'll look at the other suppliers you've suggested. After 30 years of seclusion in electronics and firmware, my lack of machine rebuilding know-how will have to be supplemented by the most installer-friendly package available, if success is to be an option. > Wherever you shop for screws, make sure you get confirmation that the > screws have adjustable preload, and that you are getting the other > features you want. Vendors don't seem to want to give specific > answers, so you'll need to press them for what you want, or just move > on to someone else. Don't assume anything, like I did. But we all do in effect, because in the beginning we don't know enough to know that we're making assumptions. You know that flattening the learning curve for those who come after makes you a guru, don't you? :-) One of my go-ogles hit a thread on CNCzone, where clamping a "wave" washer between two ballnuts was used to provide preload. I don't know how it compares price or reliability-wise. > This could take time so you may want to get your acme screws going > first. Yes, even if I have to gear down further, due to higher friction, it will be encouraging to see something moving. > Ideally, you should look for an old CNC that already has ball screws. > I bought my Shizuoka and converted to EMC2 for less than $2500. > http://www.wallacecompany.com/machine_shop/Shizuoka/ I'll try that, but I've only seen larger CNC machines offered for sale here in Australia, and only by dealers, with resulting high prices. It's probably necessary to actively express interest in the right quarters, to have any chance finding something affordable. But not everyone would be interested in an older machine with a bung controller. ... > Others have used the quill rack and have been satisfied. Check out > CNCzone.com for examples. Thanks, I'll do that. When milling manually, the 0.008" quill rack backlash hasn't yet been a problem. If EMC's backlash compensation leaves anything to be desired, then it's not difficult to add extra lines of gcode to overshoot a retract, so that all depths are approached from above. > I prefer putting a ball screw on the knee. Or even better, remove the > head altogether and fit a new slide and CAT 30 or 40 spindle instead. > If needed you could refit your old head and be back where you started. The machine is fitted with INT30, which looks just like the "Quick Change", pictured second at: http://wiki.xtronics.com/index.php/Tapers Cranking the knee up and down for every tooth on e.g. an HTD pulley, would be enough to make me _really_ want to do it in one pass, and would need a big motor. (Hand-cranking that axis is good exercise) The quill dancing up and down daintily, as the rotary table pirouettes, should involve less groaning and less time, I feel. > > Yes, stopping to think it through, with the encoder on the motor or > > leadscrew, backlash after that isn't a feedback issue. > > But it may be a positional and surface finish issue. The table will > have uncontrollable movement within the backlash. With manual > machines, the better machinists will lock the axes during a cut, and > always come up to a location from the same direction. You can try this > with your CNC but it's not common practice. Before starting on this, I'd imagined pneumatic or small-motor operation of the slide locks. But leaving the knee manual, and manually locking that axis, keeps things simpler. Following your admonition about uncontrolled movement, locking X or Y when it is static, could be back on the radar, if ballscrews are too sensitive to be installed with hand alignment. > Good luck, be patient, have fun. Many thanks - I'll definitely do that. I don't know what I'll make with the machine, but when I started with microprocessors 30 years ago, it was making iron dance to its tune which fired my imagination. Now I have time to try it - just for the fun of it. :-) Not knowing anyone in the region in this hobby, I find that this list's good humour, helpfulness and practical good advice do much to make it more fun to tackle the task. Erik -- All we have to decide is what to do with the time that is given us. -- Gandalf the Grey ------------------------------------------------------------------------------ OpenSolaris 2009.06 is a cutting edge operating system for enterprises looking to deploy the next generation of Solaris that includes the latest innovations from Sun and the OpenSource community. Download a copy and enjoy capabilities such as Networking, Storage and Virtualization. Go to: http://p.sf.net/sfu/opensolaris-get _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
