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 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. 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. 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 be can set blocks to near perfect plumber and level On Sat, Sep 8, 2018 at 4:18 PM Gene Heskett <ghesk...@shentel.net> wrote: > On Saturday 08 September 2018 18:30:42 Chris Albertson wrote: > > > This has already been done on Merlin. Merlin is the software that > > interpret g-code for most 3D printers. > > > I see, but that also is dealing with what effectively is a plain one > dimension rendered in 3d. > > A lathe is a slightly different critter, and the major src of the error > is the tilting of the carriage in and out due to different amounts of > wear front and rear, so the correction consists of moving a dial along > the centerline height, and measuring this in and out wobble the tilting > creates and applying an in or out correction of 3 thou maximum, so the > cutting tool effectively follows a straight line. > > Due to the wear createing a height of tool motion, its acknowledged but > unless working on a eighth inch or smaller part, this height change is > surely under 0.001" in effect on the part unless its super teeny. > > > The way it works is there is a distance sensor on the print head and > > it probes the entire bed in a grid pattern. It ALWAYS finds that the > > bed is not level and not flat. There are several kinds of probes > > sorted. One is a simple microswitch. > > > > Then after probing the bed and seeing that it is not flat or square > > it computers a transformation matrix and then later all X,Y,Z values > > in the g-code are transformed. In the end you have a part that is > > perpendicular to the bed but maybe not vertical. Depending on where > > on the bed your part is it might be leaning in a different direction. > > > Again, an effect that on a lathe, that is quite miniscule, and with only > stepper motors to microstep control, plus the lash in the ball nuts and > thrust bearings, is quite low. So low that its a non-problem if not > working on the hubble mirror. > > > It works well within reason. Actual errors need to be only a few > > thousands. In my case the bad is slightly bowel shape with the > > =center being about 0.2mm deeper than the corners. This level of > > error is easily corrected. > > I assume you meant "bowl" shaped. :) > > Do we have a receiver/logger module for the digital output of a scale I > intended to put on the tailstock barrel, one of Shar's lower cost models > with a remote display. This, fed to some math to detect the high and low > spots and how high or low which would allow the error to be logged. I > could mount it in a tool holder and put a teeny ball bearing to ride the > calibration rod, and rubber band its slider toward the rod. Its a > thought anyway. I'd have to obtain the data cable, or just log it from > its own display every 1/4" if no recording module is available. > > At least I would have a good starting point, which may in fact be "good > enough for the girls I go with". > > Thanks Chris. > > > > On Sat, Sep 8, 2018 at 12:23 PM Gene Heskett <ghesk...@shentel.net> > wrote: > > > Greetings all; > > > > > > I am about to give up on this bedwear comp project. > > > > > > How I determine the amount of correction needed has been tried by > > > watching the dial as Z is moved, taking notes as to which way the > > > center of the wobble (the spindle is running about 15 rpms) moves, > > > and putting that DRO's RAD in the hal files lincurve "setp" list. > > > Makes it worse, change sign of lincurve y-val, still worse. Seems > > > like the correction is being multiplied by 3 or more. > > > > > > I have run it to a lincurve X-val-nn point, and using the jog dial, > > > centered the dials wobble on zero, then put the obtained rad into a > > > y-val-nn, again making it worse with either sign. > > > > > > So how do you folks derive the correction needed? > > > > > > I'm assuming the offset itself is in radius, not diameter. In which > > > case the needed radius correction max's at about 2.5 thou. And that > > > the sign is the "tricky" part. > > > > > > Thanks everybody. > > > > > > -- > > > 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 > > > > -- > 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
