I would like to add rigid tapping. Those are some inexpensive encoders except the top rated speed is 5000 rpm and I have a 10000 rpm spindle. Any suggestions regarding suitable pulleys to reduce the speed (perhaps 5:1)? Will normal GT2 belts survive?
> -----Original Message----- > From: Chris Albertson [mailto:[email protected]] > Sent: Friday, June 19, 2020 2:02 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Universal spindle speed control for $7 > > 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:AfUAAOSwQ0dcxosi> > > 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. 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/dp/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 > > > > > -- > > 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
