On Friday 19 June 2020 14:01:54 Chris Albertson wrote: > There is all the space I need to build an encoder for the HF mill's > spindle. The sensor will fit above the drawbar. > > I'm thinking of using this sensor. The shaft would point down and > thesensor is aligned with an directly over the spindle. > ebay.com/itm/360-600P-R-Photoelectric-Incremental-Rotary-Encoder... > <https://www.ebay.com/itm/360-600P-R-Photoelectric-Incremental-Rotary- >Encoder-5V-24V-AB-Two-Phases-Shaft/254214673272?hash=item3b30601378:g:A >fUAAOSwQ0dcxosi> > > There is a cover over the spindle that is held on by friction. It > looks like the top on a can of spray paint. I can make a > replacement that is held on by magnets. Inside is the encoder that > fits on top of the drawbar. The sensor is fitted with a 17mm "socket" > that is light friction fit to the top of the drawbar. > > In use, I'd remove the new cover and stick it on the side of the mill > using the magnet, apply the wrench to the drawbar then replace the > cover. > > I am trying to decide if I want a 360 line or a 600 line encoder.
If you've the bandwidth, use the 600, if not, a lower one will work but at a little less Pgain. With the servo lag, use only a teeny bit of Igain. > Either will send data too fast for a printer port with no Mesa card. > I might put a microcontroller in the cover and use a serial interface. > The plan is to get spindle speed control to run open-loop first. I > figure an open-loop servo-controlled pot is at least as accurate as a > human operator can do with his fingers while listening to the noise. > > My pendant project got a huge boost when I figured out I don't need to > build any hardware. I can use an off the shelf X-box USB game > controller. I already have a few of them. > > On Fri, Jun 19, 2020 at 4:11 AM Gene Heskett <[email protected]> wrote: > > On Friday 19 June 2020 06:10:48 Roland Jollivet wrote: > > > I was going to suggest this at the start of the thread, but I > > > thought it would be considered too Heath Robinson.. > > > > And within its limitation of available torque to keep the tap > > turning, and an encoder able to track to a 5 degree accuracy, I see > > no reason to totally eliminate rigid tapping from its abilities. > > Even the little 200 watt hf mill should be able to turn an 0-80 or > > maybe even a 2mm tap. The lack of space in the head to build a > > decent encoder is far more of a limitation than a speed controller > > such as this. Thats the main reason my little hf never grew the > > ability to tap, That controller/amplifier, pulled out of the head > > and mounted in a 4x6x3" box so all the the hot electronics was out > > of sight, proved to be a very high gain controller, so high gain I > > was forced to rig an ammeter to tell me how hard it was working so I > > could control the cost of fuses, there was otherwise no slowdown to > > let the user know it was working too hard. > > > > I eventually blew that controllers pass transistor, a simple powet > > F.E.T., and in search of a suitable replacement, checked the bugs in > > an out of spec pc supply from the junk box, found it was rated at > > 800 volts instead of 200, 12 amps instead of 2.5, but otherwise > > looked the same. So the consideration resolved to the driver > > transistor in the circuits ability to switch the much higher gate > > capacitance that bug had to have since switching speed is paramount. > > I put it in, think I had a reservoir of such bugs if it didn't work. > > I raised the fuse from 2.5 amps to 4. > > > > That was over a decade back. I've blown the fuse 2 or 3 times since > > with the ammeter pegged, but its still there although the rest of > > the mill is in pieces, it unscrewed one of its ballnuts a year & 1/2 > > ago. > > > > Somebody should make me an offer for it, its the complete controller > > out of the big head hf x1 with a pmdx-106 interface, ready to take > > the pwm & direction output of LinuxCNC from a parport bob, either > > manual or full bi-directional computer control of a 200, maybe even > > a 400 watt motor. Its not in service here, and probably won't ever > > be again as I'm approaching the end of my ride here with a pump > > running at 31% efficiency. And thats beginning to affect my > > giddy-up. > > > > > On Thu, 18 Jun 2020 at 20:40, Chris Albertson > > > <[email protected]> > > > > > > wrote: > > > > I'm making good progress on my 3D printed CNC conversion. I > > > > found a way to 3D print a spindle controller that should work > > > > for most small milling machines and small lathes. The cost is > > > > "almost nothing". These machines' spindles are controlled by > > > > turning a potentiometer so my new system simply uses a cheap > > > > model airplane servo to turn the shaft of a potentiometer. The > > > > computer is 100% isolated from any high voltage or noise. > > > > > > > > These small mills will never be able to do things like rigid > > > > tapping so all they need is a simple and approximate way to > > > > control the RPM. This speed control can be run "open loop" if > > > > plus/minus 20% is good enough or used with a spindle encoder in > > > > a closed PID loop as long as the PID is tunned not to > > > > aggressively. > > > > > > > > > > > > For anyone who does not know about these hobby servos: > > > > > > > > - They are not full rotation motors. They turn only through > > > > about 250 degrees, This is a good match to the pot as pots also > > > > rotate about this range. > > > > - The angle of the servo shaft is controlled by a PWM signal. > > > > - They are "dirt cheap" starting at about $5 > > > > amazon.com/4-Pack-MG996R < > > > > https://www.amazon.com/4-Pack-MG996R-Torque-Digital-Helicopter/d > > > >p/B0 > > > > 7MFK266B/ref=sr_1_2?dchild=1&keywords=mg+servo&qid=1592502600&sr > > > >=8-2 > > > > > > > > - They accept a 5-volt control signal, so they have a > > > > built-in computer interface. > > > > - They are fast (enough) and can move from full-low to > > > > full-high on 0.6 seconds > > > > - They really are actual "servos" and have an encoder, motor > > > > driver, and gears all inside. > > > > > > > > > > > > So when LinuxCNC outputs a low-value PWM spindle control, the > > > > servo moves the pot to the low position. As the PWM signal > > > > value gets larger the pot is moved closer to the high-speed > > > > position. > > > > > > > > In the picture below is a cartoonish render. The green frame is > > > > one-piece 3D printed, The red pannel and tan coupler are also > > > > 3D printed. The motor sells on Amazon, four units for $20 and > > > > the pot is about a buck each. Four M4 button head screws > > > > everything together. > > > > > > > > Here is a link to the current version CAD files and a viewer. > > > > I'll be updating the files after the first prototype is printed. > > > > https://a360.co/2N95AiL > > > > I may make a top cover to protect the pot and keep fingers off > > > > the high voltage. > > > > > > > > > > > > > > > > [image: Red Neck Spindle Control v6.jpg] > > > > > > > > > > > > > > > > -- > > > > > > > > Chris Albertson > > > > Redondo Beach, California > > > > _______________________________________________ > > > > Emc-users mailing list > > > > [email protected] > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > _______________________________________________ > > > Emc-users mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > 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) > > If we desire respect for the law, we must first make the law > > respectable. - Louis D. Brandeis > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
