On Monday 12 May 2014 15:23:39 Marius Liebenberg did opine And Gene did reply: > On 2014-05-12 19:13, Gene Heskett wrote: > > On Monday 12 May 2014 10:48:52 Marius Liebenberg did opine > > > > And Gene did reply: > >> Will it be possible for me to read an encoder signal on my lathe > >> spindle with a normal parport input. I will fit a Hall effect Sensor > >> or an Interrupted light source signal. The max RMP will be 2000 and > >> I might have 10 slots or more. > > > > It is not a problem at those rpms Marius, my encoder is led > > interrupter based and has 50 slots with the interruptors spaced for > > quadrature output. By my calcs, I can probably track it to nearly > > 6000 rpm. So I quite worrying about it 2 or 3 years ago. > > > > Here is how to get a rough idea, assuming the read encoder function > > is in the base thread. My base thread runs at 27500 ns, converted > > to a frequency by the usual math, is 36,363 times a second that the > > port and encoder data will be updated. Now, and this assumes a > > nearly 50% duty cycle from the A/B slots of the encoder wheel get at > > least one sample per state of the quadrature signal generated. > > Overtaking that will raise the apparent noise in the velocity signal > > by quite a bit. Most of the time you are under it but and several > > identical samples per state. > > > > Since in my case an edge occurs 200 times per rev, and the base > > thread is 27500 ns in this example, then calc how much time it takes > > edge to edge by taking the rpms/60 to get the scale in seconds, so > > 2000/60=33.333333333333333333 rps. > > > > Now, 200 edges per turn is 33.333333333333333333 *200 = > > 6,666.6666666666666667, the resultant frequency of the edges. > > So in my case, 2000 rpm is about 1/6th of the speed I can track it > > at, or around 12,000 rpms. I hope my math is correct. ;-) > > > > The more slots you have, the smoother the Z drive will be when > > cutting threads or some such. 10 would be pretty coarse. > > I realized that I could have a lot more slots. 50 sound good to me as > well. I will have a disc laser cut to be very precise. Ans also one > does not cut thread at break neck speed so I could afford a higher > number of slots. On the lathe I normally cut at a spindle speed of > about 45 RPM but I guess that could become a lot faster once the cnc > conversion is completed. > > > Cheers, Gene
I commonly thread (g76) at about 500 rpm, but the stuff I cut is not more than 7/16 SAE, some USS or 10mm x whatever. The forward trace when its at cutting depth is done at about the same speed as the retrace, although I just had a Z freeze after about 4mm of retrace, cause unk, couldn't find any grit in the Z reduction gearing, but the heads of the browning pull screws in the hub were making a 2 or 4 thou deep trench in a mounting bracket, so while I had it apart to replace the spindle drive lower pulley and belt, (that stripped the bars off the lower drive pulley) I cleared off about 20 thou off the top of the screw heads, and cut the stepgen_maxvel and maxvels about 20% since I had made them monstrously huge as an experiment in seeing if I could reduce the speed dependent bias angle of the z take up at the synchronize point. Its minor at 50 rpm, major fraction of a spindle rev at 500 rpm when normal stepgen_maxvel limits are in place. If I ever find my round tuit, I am going to see if I can modify the basic lock step code in G76 and G33 so that it starts the sync move at a false index internally generated in advance of the real pulse to take place such that sync has been achieved within a couple degrees of the real index pulse. Then we could cut threads at any rpm without the thread walking along the Z axis when we vary the spindle speed. Since in the reassembly, the encoder disk will not be aligned with the chuck, I'll have to reset the OD about 1.5mm larger, and then start trimming the Z_start position to see if I have a snowballs chance in hell of finishing that thread cutting run as the nut will not go fully on the threads it had cut when the Z stall took place. And I do not have an 8mmx1 die to finish it. Fun and games, NOT! Cheers, Gene -- "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> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
