On Saturday, 2 April 2022 10:04:58 EDT [email protected] wrote: > Agreed about making an encoder and I have an Omron unit with A/B/Z > outputs "in the mail" from China. > > The drawbar for my R8 spindle extends out the top of the spindle. It is > a hollow shaft encoder with an 8mm through hole but that is > insufficient to accommodate a drawbar. I suppose that I could couple > it to the top of the drawbar with some sort of slip coupling but that > has potential issues with alignment and coupling backlash. Perhaps I'm > not looking at things the correctly but it seems that the simplest > approach is using a pulley and belt to offset things. Also, the > encoder is rated for a maximum of 10000 rpm and that is my max spindle > speed; I could reduce with a 2:1 pulley + belt.
reduction will muck with the index, so stick with 1/1 pulleys. R8 spindles with the draw bolt sticking out of the top, are a dangerous place to put an encoder. I tried to make en optical bolted to the top of the drwabar cap but the room available and the tooling to cut slots so small, I was not able to make a disk accurately enough to work well, and for some reason, the 2-56 screws holding it to the drawbar cap kept coming loose which allowed the disk to saw blade thru the optics. So I bought an omron, and made an extension shaft for the rear of the motor shaft, drilling into the center dimple of the shaft and tapping it, and drive the encoder from there, but its about 7x faster than the spindle. I also put a piece of cut off steel screw rtv'd to the side of the drawbar cap and rigged an ats-667 hall effect sensor to use its as the index as the gearing between the motorshaft and the spindle made the encoders index into a random position signal. I fixed the gear ratio by adding switches to the gearshift knob and a bit of math in the hal file switches with the gears, so a tkinter tach dial remains dead accurate. Not knowing the gear ratio, I added some more hal modules to follow the encoder for 100 turns of the spindle according to the index pulses, and I'm lazy so I automated that so it displays the encoders count difference after 100 turns. Divide by 100, and put that into the SCALE for the spindles ini settings. Did that for both gears. Obtained the ratio and switched that in and out with the knob tallys in the hal file. With the better encoder, and its reduced quantization noise, I was able to use about 20x as much Pgain and more of both Igain and Dgain. My only problem is the non-simetry of the ats-667, its polarity changes with the direction and stays there until the next time the screw is approaching which resets it, then the actual, on time pulse is the second edge it outputs, but the edge direction is up for one direction, and down for the other. So it changes about 15 degrees depending on the direction, and that, in my thinking is a cause of the sloppy threads I get when rigid tapping. And it isn't helped by my g0704's column being a tad off vertical, so there is a slight sideways motion as it descends, tending to push the tap sideways as it descends even if very accuratly trammed. That I can fix, I just have not gotten a round tuit, with an offset module, maybe 2 driven by a scaled way down Z position. I *have* acquired the circular square to verify the correction. Its what you get when you buy the cheapest chinese mill almost big enough to be usefull. Putting ball screws and motors on the Grizzly G0704, was $1100 when I bought it. But ball screws does NOT make a silk purse out of the infamous sows ear. But it is one possble solution to Leonardo's problem. If Leonardo, you want to look at my .hal, & borrow some of it, pm me your email address and I'll attatch it to a reply. Take care and stay well. 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, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
