On Saturday 26 January 2013 07:46:43 Greg Bentzinger did opine: Message additions Copyright Saturday 26 January 2013 by Gene Heskett
> Gene; > > Have you considered extending your screws and mounting a (relatively > cheap) CUI encoder on the far side of the screw and using the index for > homing and the A/B outs as a DRO or a lost step check? No I hadn't. The lost step check might not be such a bad idea though. Main thing is a general lack of sufficient I/O pins to put it all together without additional Mesa goodies. I have always intended to tie some sort of a motor stall or electronic fuse lashup into the last I/O pin I have left, assigned as an E-stop on paper but the sparkfun gismo to do that is still in its teeny little box sitting in front of the printer here. My z drive, with its 2/1 gear down to the oem 16 tpi screw, when translated to this 5mm pitch, won't have the push I had before even if the ball screw is far more efficient, so I am mulling over the idea of an even higher gear ratio being done with cogged belts. Both motors are triple stack nema 23's, 425 oz. The 8x2.5mm screw in the crossfeed seems to be an excellent balance between speed and available force with its 8 wires wired in series. Speedwise, .0625" a turn is 1.58mm a turn, this screw is 5mm/turn, so my 40 ipm becomes about 120 but the force available is reduced (ignoring the considerable friction is the old screws half nut) so there could be a possibility of lost steps that wasn't a factor before. Its just that I can't see the utility of 120" rapids on a lathe, particularly in view of the extremely puny powered spindle drive. Its rated as a 7" lathe, but doesn't have the spindle power to cut a continuous chip .003"x.003" in alu at more than 1" radii, or in steel at a radii above .6" and does really get into the mood to throw blue curlies 3 feet long until its down to about .4" radii or less. It will of coarse help when I wire the z motor in series, which will allow the design torque that I am a bit short of now since the driver can't do the amps for full torque wired parallel by about a 20% shortage. So there might be enough to do the job. Going to series wiring will cost motor rpms, but with this new 5mm screw, I got them to throw away. Either way, the real bottom line is the missing horsepower in the spindle, and the rubber in the 7z12 frame. And at some point, the compound feed has got to go, its a major part of the rubber problem with its inability to support the tool in a position that doesn't tend to lift the far side of it, or the carriage, from the off center cutting forces. So eventually it will get replaced by a solid block of steel with the QC bolt hole offset to the right about an inch so the cutting forces are much better centered over the middle of the carriage. Even the stock, square block tool holder has this problem. It should have had a lantern post holder from the gitgo. I tried to make one but to do the cup & rocker properly would have required about 3/16" to be milled off the top of the compound, and its tool holder bolt threads aren't deep enough now. That I expect will be precipitated by the failure of those 10mm threads again, they were stripped out once before, needs at least another 2 threads of depth in that cast iron for decent strength. That failuyre will probably happen the next time I need to use my "big" boring bar. Its a 3/4" piece of round cold roll, in a hard steel clamp block that 10mm bolt holds and closes, with a groove milled in the side, and the 5/16" by 4" indexable Glannz boring bar pressed and superglued into the groove. About a foot long, it actually works well enough to get the job done with one of my bench rest shooting bags draped over the right end to damped the chatter to a dull screech. But when extended about 4.25" while boring that drive adapter housing you can see on my rotary table on the web page below, it had enough leverage to pull the threads out of the top of the compound. That, at the time, precipitated me getting back in practice for reciting my famous 5 minute, non-repeating, unprintable monologue. :( > BTW take some pics as this goes together. I really should do some updating there. jigl doesn't update an already generated slide show as easily as it should, I'd like it to order the slides by creation date putting a bit of order into the chaos it and linux generate by alphabetizing. I suppose some creative renaming could cheat, never tried it. Hummm. Now all I have to do its convince my ancient wet ram to remember that when I next add & remove pix. That, at my age, isn't funny even if I do make jokes about it. One has to, to keep from shooting the local cats. Some folks would say we have a surplus of them, but at least these aren't feral. We did have one that was and wasn't, but he "left the building" after a scrap with a fixed pussy the BH was feeding that cost me a vet bill in excess of $250. Thanks, Greg Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> Truly simple systems... require infinite testing. -- Norman Augustine I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft MVPs and experts. 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