> On Apr 10, 2024, at 1:14 PM, gene heskett <ghesk...@shentel.net> wrote: > > On 4/10/24 13:30, Chris Albertson wrote: >> Do you even need a rotory table to cut a spiral? > > Now that you ask, I think the answer is probably no. Take a look at the nurbs > command G5.2 where a group of points describes the curve. Then rotate the > points about one end in polar/rectangular space. I haven't played with that > myself, perhaps Andy has a better way?
If you know how to find the 3 or 5 or 10 points that define the curve, then you can use the same method to find 10,000 point on that curve and just do a straight line between them. Finally to TEST your idea, you need a way to calculate the error. You find the exact solution for any arbitary point and then to compare that to what you are doing. If you know how to calulate the exact solution, then why bother with approxomations like nurbs? The nuirbs thing is for filling in points you have no way of knowing. What nurbs is good for is when you want to mill a copy of some object that you don’t have an exact solution for. The perfect example is that you were given an STL and all they have is triangle vertici. You can’t know where the STL got its shape, is the curve a circle, elipse or an artest’s pen stroke. But the nurbs-like or spline-like fitting funtion will generate a smooth curve through the list of points. >>> On Apr 10, 2024, at 12:09 AM, gene heskett <ghesk...@shentel.net> wrote: >>> >>> On 4/10/24 01:57, John Dammeyer wrote: >>>> A friend and I have been discussing exactly how to write the G-Code to >>>> create a spiral scroll. >>>> His rotary table 90:1 reduction with a 1600 micro-step motor could be set >>>> up >>>> to move N steps for each step of the X axis to create the spiral. But that >>>> approach seems clumsy. >>>> Say I wanted to cut a scroll with a 6mm pitch using a 3mm cutter. >>>> Without using G2 or G3 it's really just a triangle isn't it? Move rotary >>>> table distance A and move X axis distance A'. Do it in small enough >>>> increments and you get a spiral. But I feel like I'm missing something >>>> really simple. >> Do you need a rotary table to cut a spiral? It is just a series of >> locations in (x,y). OK, if you wanted to use only (say) the X and A axis >> then you should use polar coordinates, not cartesian. The equation of a >> spiral on polar coordinates is very simple. Then you evaluate itat many >> thousands of points and at each point write gcode to “cut to” that point. >> You would not need the rotary table. >> Also why think in micro-steps and worm gear rates, you are using LCNC to do >> the kinematics, Use millimeters. >> I think this problem shows that in some cases you really can not write the >> gcode by hand. FOr continous curves in (x,y) there might be 100,000 or more >> lines of code in the file, especially if you don’t do the cut in one pass. >> You would nee towrite software to generate the g-code. Or use existing >> software, a lot of CAD systems will do this for you >>> First, a 90/1 is quite high. I have two rotary's, both consisting of a 3NM >>> 3phase stepper/servo I made by combining the 3NM motor with a 5/1 worm. >>> Using a screw in the worms output hub as a single prox sensor index pulse >>> generator. To calibrate a complete rev, I measure the steps by starting the >>> count on the 3rd turn ans stopping the count on the 103rd turn, which gives >>> me a scale*100. Shift the decimal point 2 places left this becomes the >>> scale for the axis in the .ini file. All this math in linuxcnc is floating >>> point so I can ask it for 33.333 degrees and it will run to what it thinks >>> is 33.333 degrees. This stepscale: >>> STEPSCALE = 22.22222222222 = 1 degree >>> So one count is about 1/22.22222222222 degrees, probably less than the >>> backlash in the rvs39 worm, a pretty cheap worm. >>> >>> Currently to make one of my maple vise screws, starting at 0 degrees its >>> around 60,000 degrees it turns for around 400 mm of screw that y travels. >>> Then I lift the tool, turn it another 180 degrees, re lower the tool and >>> bring y back to zero and b=180. Makes a perfect two start buttress thread. >>> The B is turning, in perfect sync with the Y motion, at something in the >>> 300 to 400 rpm range. That 3NM motor is heating but not dangerously so. >>> >>> There is no reason you couldn't lay it down to make a C drive, and >>> simultaneously drive X Z & C to carve an impeller in a quite serviceable >>> scroll. >>> >>> The versatility of the closed loop stepper/servo, which does EXACTLY what >>> the TP tells it to do, without a PID in the path, is amazing. I have them >>> rigged to e-stop linuxcnc in about a millisecond if they make an error, >>> like losing a step. Tested till the cows come home, has yet to happen >>> working a job. I haven't hobbed any gears, but it certainly seems accurate >>> enough to do it. >>> >>>> Suggestions? >>>> Thanks >>>> John >>>> _______________________________________________ >>>> Emc-users mailing list >>>> Emc-users@lists.sourceforge.net >>>> https://lists.sourceforge.net/lists/listinfo/emc-users >>>> . >>> >>> Cheers, Gene Heskett, CET. >>> -- >>> "There are four boxes to be used in defense of liberty: >>> soap, ballot, jury, and ammo. Please use in that order." >>> -Ed Howdershelt (Author, 1940) >>> If we desire respect for the law, we must first make the law respectable. >>> - Louis D. Brandeis >>> >>> >>> >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> >> https://lists.sourceforge.net/lists/listinfo/emc-users > > Cheers, Gene Heskett, CET. > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author, 1940) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
