G33 for the win! sam
On Wed, Apr 10, 2024 at 12:31 PM Chris Albertson <albertson.ch...@gmail.com> wrote: > Do you even need a rotory table to cut a spiral? > > > 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 > 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
