On Saturday 13 October 2018 04:49:40 theman whosoldtheworld wrote: > I'm sorry but my English is rubbish ... you're trying to measure and / > or chase the ripple of a sheet metal for a laser system (measuring or > cutting .... for example, like those used to cut gold ?) > > bkt > > Not quite that.
I have a laser cartridge made to look like a 38 caliber pistol cartridge, with its back battery cap removed and about 22" od .375" brass tubing threaded at 50 tpi screwed into that, with a teflon plug in both ends, and a brass screw in each teflon plug, with a wire between the screws. I've made a pair of spring contacts, one to ride the OD of the tubing sticking out of the rear of the spindle, and one to ride the screw head on the end. + terminal of a 1.7 volt wall wart to the tubing, - to the screw. So the laser is running on a stable supply but dimmer than if it was running on 3 volts and 15 USD worth of batteries. It is mounted in an 3/8" er20 collet in a TTS toolholder, which in turn is in the 8"4jaw and the TTS holder had been adjusted in the 4 jaw four about .0003" runout. When the laser is powered up along with the spindle, it eccentricity at the tip of a dead center wobbles about 20 thou around the tip of a dead center, and the tailstock has been adjusted to center that wobble. With nothing in the beams path, a small CDS cell stuck in a gob of modeling clay has been mounted in the tailstock barrel, and the clay adjusted so the center of the spinning beam is on the center of the CDS cell. With the laser off, the CDS is subject to the room lighting and has a R value of about 2.7k. With the laser on, its about 250 ohms. A sheet metal piece to serve as knife edge is attached to the toolpost so it can be adjusted with the X jog dial, which I can jog the x in .0001" steps to block around half the beam, and the spindle is run at 600 revs, so the lag of the CDS cell tends to average the resistance reading. But it may be that the rev rate is too well synchronized to the DVM's A/D rate, something I'll check today by running the spindle at 625 revs to see if I can see the same reading wobble I can see at 500 revs, its quite a bit of reading wobble, about 100 ohms pear to peak at 500. I can go faster, but will need to loosen the front spindle cap to control the heat as 1/2 hour at 600 gets it up to smelling the hot 5w-20 oil. Its a bronze bearing and the spindle is slightly tweaked from a fall-over that also destroyed the compound. Its been replaced with a carved cast iron block the same height as the compound, which of course isn't needed with the computer driving the x at any angle to the y. I've very gently honed the high spots around the bed dings so they are a thou or less. This leaves bed wear, 70 years of it, mostly near the spindle, therefore I am using a point a few thou from touching the tailstock, which is carrying 3 each, pieces of 3/8" SS tubing up the right edge of the cross feed to get all the wireing from a cable chain at the rear of the carriage, to all the stuff on a new front apron replacing the old drive. The Z drive nut, the X motor and the jog dials and their mode switchs are on this 1/2" thick alu plate, bolted to the front of the carriage face. The intention is to measure the offset from a touched off to zero X at the tailstock, measureing the offset needed to maintain the same ohms from the CDS cell as the carriage is driven, carrying the "knife edge" from the tailstock back to the side of the carriage just ticking the chuck. Find those offsets, list then on paper, then edit into the points of a lincurve module, which will then autocorrect well enough to turn a cylinder within a thou even if its 4" in diameter and 2 feet long as long as its supported on both ends. But everytime I move to the calibrated point at the tailstock, I have to re-touchoff by as much a .001" so theres still a need for a better means of averaging the CDS cell to get a stable R out of it. Thats todays project, finding the lack of repeatability. Because there is a bit over .001" backlash, I always get the 400 ohm setting by pulling out, and driving it back in, which should reduce any error from x drive backlash. Its possible the laser itself isn't well centered in its holder, and further adjustments of the 4 jaw are needed to further reduce its eccentricity at the target. With the bent spindle and refaced backing plates, I might even have to resort to grinding the backing plates, I refaced them only enough to cut 100% of its face, so there could be some axial miss-alignment yet. And thats just for starters. :-) And that is what I am trying to do, calibrating a lincurve to make a worn bed fairly straight again. -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
