https://www.britannica.com/science/spiral-mathematics Several options here, take your pick. Should be trivial to move it from floating pt to fixed. May have to scale to make it happy. ;-)
Dave > 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. > 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
