The lasers are easy to find on Amazon but be warned the laser is not perfectly aligned with the housing. But as I said, this does not matter if you spin the spindle.
I think a laser is the only option. If you are measuring the bed your reference needs to be at least 10X straighter then the bed. Precsion rods are not good enough but a $20 laser is literally perfect (as long as you rotate the spindle.) With effort you can use the same laser to measure the error with the lead screw pitch. Use it as a laser range finder or laser inferometer But all this measurement may be moot if the lathe is not reputable. The error might be random. Maybe the carriage moves like a tuck on a dirt road? On Sun, Sep 9, 2018 at 6:04 PM Gene Heskett <ghesk...@shentel.net> wrote: > On Sunday 09 September 2018 18:14:52 Chris Albertson wrote: > > > No, the Software in Merlin is probing the bed using a grid pattern > > and modeling the bed's actual shape.. Iet to choose how dense is the > > sampling grid. I have a capacitive sensor but I'm going to hav e to > > change to a contact switch because I'm also changing the bad from > > aluminum to borosilicate glass > > > > On a lathe I think the hard part is finding a straight reference for X > > and Y. A laser beam would be a VERY straight line > > > Agreed there! > > > What if there was a 1mm diameter laser beam that shoots through the > > hole in the spindle? Then you mount a camera on the tool post and > > move the tool post. If the lathe is not 100% perfect the laser spot > > will move relative to the camera sensor's CCD image sensor. The > > camera needs to be more like a microscope then wide angle webcam. > > But you can buy a USB interface microscope now for under $20. Mount > > one of those to the tool post. > > > > As for the laser, I actually own one that would work and I've actualy > > used it on my lathe. It has designed for gun owners. It is the same > > size as a .38 round and the idea is you can chamber the laser in the > > gun and then a green laser beam shines down the barrel and you can use > > it to align a gunsight. It is powered by a tiny battery. You can > > make an adaptor to allow you to "chamber" the round in the spindle > > hole. > > Or it could be chucked in an er40 collet, with the "cartridge" rim pushed > against the rear of the collet. The problem there is angular since an > er40 collet has proved to me that it can and will, tilt the equ of 5 > MOA. So the spindle has to be rotating so the beam draws a circle. I > have a pointer, but its nowhere near straight like the gunsite > boresighter is expected to be. As for the camera, I have several that > might serve if the lens was removed, exposing the ccd to the beam > directly. Older cameras would be better because the ccd's have shrunk to > where the beam may even overflow the edges unless it can be tightened up > beam size wise from a whopping big millimeter. > > Its a thought I've explored while drifting off to sleep nights, several > times. But I've always had a bottleneck shaped "cartridge" in mind, but > now I'll look for "38" type since they are obviously made. > > But right now I just got an order from the missus for a coke float. She's > dying of COPD, so I always see that famous 2 rule sign about the > boss. :) > > Now, I have just come in from trying to map it again, but I am seeing a > problem in that the tool location may not equal the centerline of the > crossfeed, and that can probably effect the correction needed. Humm, but > thats an absolute carriage position that only changes if I diddle the > homing switches location. Not terribly likely in the remainder of my > ride here since I'll be 84 in 3 weeks. > > I started out about 1/8" from the er40 collet turning the rod, which is > about -5.8" from the home switch, touched x off to 0.0000 and logged the > RAD reading every .2" to about 7" away, at which point I switched to 1" > steps as I was off the higher wear by then. Finding the tailstock > off -6.5 thou, which I tried to correct, and found that a cast iron > bitch to get under a thou, so I need to assume the 6.5 thou error there > that the tailstock, and scale it down to zero by the time I get back to > the spindle, then put all those figures into the lincurve, which if I do > it right, should get me within a thou, at least for the 20" length of > that A2. And that WILL get it good enough for the girls I go with. > > > If you mount some ultra-fine graph paper on the tool post and look > > really carefully in theory you can see how the bed moves in X and Y > > vs. in Z. But there are to practical issues > > 1) It is really hard to see such small movements. I literally need a > > microscope to see. I do have a micrometer grid target. Youcam buy > > them in eBay for $13 and yes you need a good microscope to see uM size > > grid lines. The lines are laser etched on glass. $13 is not much > > It intended use is for measuring "stuff" you see in a biological > > microscope. "How long is that bacterial?" > > > > 2) the cheap laser-bullet thing is not well made. It is good enough > > fo make a gun owner happy but not a machinist who cares about > > "thousandths" in other words the runout is horrible. But you work > > around this DOn't bother to align it. The laser will tract a donut > > shape on a fixed target. and this is good enough because yo know the > > exact centerline is in the center of the donut hole. And actually > > you WANT a donut and not a dot because with more pixels you get less > > noise. The "centroid" is what you are looking to find. You can > > find the center to about 1/10th of a grid line. > > That pretty well agrees with my thinking on this, but if a mark for > angular reference is scratched into the front of the cartridge a sliver > of reynolds wrap superglued to the "low" side ought to reduce the size > of the donut if its too big for the ccd. Wash, rinse and repeat till > adequate. But don't waste time looking for perfection. Taint gonna > happen. :) > > > No not bother to make the mechanics perfect. It is easier to just get > > "close" and then measure the imperfection. expect runout and that the > > spinning laser will trace out a donut. > > > > Of course you are not actual looking at a laser dot in practice you > > are photographing the dot and using software to find the actual > > centerline. You use the laser etched grprid only once to calibrate the > > camera/optics. > > > > Lasers are like cheating when it comes to measurement and alignments. > > I used on two years ago or the first time to make a block wall. > > Never again will I use a mason's line. lasers don't sag or blow in > > the wind and even a rank amateur like me can set blocks to near > > perfect plumber and level > > Thats something I'm not an expert at. I did make a 6 block mold to make > landscaping blocks for a retaining wall, about 350 of them, 55 lbs each, > and put a good footing under them, 7 blocks high, with a french drain > behind the footer and they haven't moved in a decade. My west and south > garage walls are sitting on them, without a j bolt in sight. You can > find a few pix on my web site. > > [...] > > Thanks Chris. > > -- > 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-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
