On Sunday 27 January 2008, Kirk Wallace wrote: >On Sun, 2008-01-27 at 14:09 -0500, John Kasunich wrote: >> John Kasunich wrote: >> > For measurements every inch, you can often find jig-borer micrometer >> > sets on ebay or other surplus places, often mis-listed as inside mics >> > like this one: >> > >> > http://cgi.ebay.com/PRATT-WHITNEY-10-PIECE-INSIDE-MICROMETER-SET_W0QQite >> >mZ140200200097QQihZ004QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewIt >> >em >> > >> > (7 hours to go, $22.50) >> >> Another couple sets: >> >> http://cgi.ebay.com/INSIDE-MICROMETER-AND-END-MEASURE-SET_W0QQitemZ3500173 >>55826QQihZ022QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewItem >> >> Missing a few parts, makes it less interesting to most buyers, but it >> has three 12" standards, so it can do 1" to 51" in steps of 1". No bids >> so far, with less than one day to go, and an asking price of $20. >> >> http://cgi.ebay.com/PRATT-WHITNEY-11-PIECE-INSIDE-MICROMETER-SET-0001_W0QQ >>itemZ330206299195QQihZ014QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewI >>tem >> >> This set is complete, has 3 bids ($10.50) so far, and will probably go >> up a bit. >> >> There are a few more as well. >> >> Even cheaper would be a set that is missing the micrometer head. >> However, they'll be harder to find because they're more likely to be >> mis-listed as something else. Perhaps search for Pratt & Whitney or >> Lufkin, since the rods are usually marked with the makers name. >> >> Like anything, its possible that the rods are worn and no longer >> accurate. You can do some testing, by comparing for instance a 12" rod >> to another 12" rod, or to the sum of a 6" and two 3", etc. In general >> though, people tended to use those things gently. >> >> Regards, >> >> John Kasunich > >Thanks John, excellent idea. Even if the rods are a little off, I >suppose you could have them professionally measured. Any rod would be >good as long as you know accurately how long it is. > >This is more expensive, but may be another possibility: > >http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230216180586 > > >No ideas on DIY laser encoders?
I sort of discounted that idea because of the difficulty in getting a single frequency out of them. In addition to the link in my last message, Massa may have a transducer that's both cheaper, and more suitable for this. < http://www.massa.com/air_products.htm>, pull down to the E-188/220 links. We can generate a much more stable single frequency signal to drive it with for probably 1% of the cost of the laser. This site also has a link to an information data page that explains and quantifies the error corrections needed quite well. I did just think of one problem, one commonly related to microwave transmission systems and just as applicable here. The emitter transducer and the receiver will both have to be several diameters above the table we're measuring else "First Fresnel Zone" effects from the reflections off the tabletop will tend to give us some cyclic errors, generally detectable by seeing a wobble in the received signals amplitude that is not a straight line distance vs attenuation derivation. A mount 6" above the table should be more than sufficient to eliminate that effect to the undetectable range. That would also take advantage of the 6 degree (or less) total beamwidth most of these have to reduce that same effect over the ranges we might want to measure. The tabletop will be out of the main beam. -- 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) Never trust an operating system you don't have sources for. ------------------------------------------------------------------------- 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
