Motor and Gearbox for a Computerized Mirror Grinding Machine
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- Опубліковано 16 лип 2024
- Gordon Waite shows you the 3-phase motor and VFD (Variable Frequency Drive) that he is installing on the computer-controlled mirror grinding and polishing machine he is building. The machine is geared down with a 30:1 gearbox. This allows the easy selection of slow speeds for polishing, and fast speed for grinding. The VFD is a special unit that provides constant torque at any speed.
- Наука та технологія
just amazing gordon! a real pro equipament... here in brazil i use an old 1/4 washing machine ac motor and a combination of pullies to polish and grind my mirrors... all homemade and mad max style! heheh
We're just about getting started on a fixed post design (based on your work) scaled up to 1.8m (70") diameter. 3 HP motor with a similar worm drive + VFD arrangement. I hadn't seen this video before, so it's good to see that we're on the right track. Is there a specific resource out there for designing fixed post turntables btw? Great work and thanks for sharing.
If you run the motor at a slow speed, the fan on the motor shaft may not provide enough cooling to the motor. A separate fan may be needed for cooling.
I've been using this setup for years, and haven't yet had a cooling problem. If ambient temperature was over 75F, though, then you might have a concern.
If I use 750watt 48 volt electric cart BLDC motor with its own speed controlling system can it work? It comes with 48v 50amp battery charger and that can be used as a power source for the set up instead of using expensive batteries.
Any thoughts would be appreciated..
BTW it's also a nice setup. Thanks
That can probably work. Good luck!
I'm considering making a fixed-post grinding machine and have an opportunity to get a used industrial 3-phase motor to drive it but it's only 250W, but with gearbox. I think the 880/42 on the label means it's 880rpm motor and 42rpm output so about 21x reduction. Do you think that might be enough power to not stall out when working on mirrors up to say, 14"? btw, all your videos are really helpful, succinct+comprehensive and always very interesting.
That motor can probably work, as long as you have good bearings under the turntable. For hand work, it's nice if you can get down to 3 to 5 rpm's. For fixed-post work, you'll want 40 to 60 rpm's.
@@GordonWaite thanks a lot for the reply and input!
@@GordonWaite p.s. have you seen this machine? Looks amazing: ua-cam.com/video/a-AGCwOcetM/v-deo.html "Spiegelschleifmaschine"
Pretty extravagant setup. At this point, a DC motor would be a lot simpler and cheaper. I don't understand the point of the gearbox in combo with a Variable Frequency Drive ?? A lot of AC motors, if not most, have a centrifugal switch to bypass the starting capacitor, once it's up to speed. Running them at a slower speed with the cap still in the circuit is a recipe for problems. The bottom line is that AC motors were never intended for variable speeds and resorting to these complex expensive solutions isn't what most knowledgeable people would do. You don't need such precise speeds so a pulley system is the way to go, if you don't want to invest in a DC motor. Last but not least, there are some pretty heavy duty stepper motors out there also, - granted the steps could impart mirror defects - not to mention servos.
Hi, Joe. I don't think you quite caught the actual components in my machine's configuration. This isn't a 120V single-phase AC motor. It is actually a 3-phase inverter-duty AC induction motor. This type of motor does not have a capacitor in it. The 3-phase motors have a natural rotation order of the three phases. So they self start in a chosen direction consistently. So with three-phase motors you never have to worry about problems running at slow speeds. About the VFD and gearbox... The fundamental speed of the motor is 1800 rpm's, depending on the frequency of the current. I want a range of 0 to 60 rpm's, so putting a 30-to-1 gearbox on the motor gives me a perfect 0 to 60 output speed range. That range comes by using the VFD, which produces three-phase output at any frequency over the range of the motor. So at min frequency, I get 0 rpm's and at 60 Hz I get 60 rpm's. The other point of the gearbox is that three-phase motors have very little torque at low speeds. By attaching the gearbox, I can run the motor at 150 rpm's to get 5 rpm's at the output. If I ran the motor directly at 5 rpm's I would have very little torque. But with the gearbox, I have plenty of torque, even at my lowest needed output speed. As to using a pulley system, that wouldn't be practical at all in my shop. I use all sorts of different speeds when making mirrors. On small mirrors doing fixed-post grinding or polishing, I need 60 rpm's. Midsize mirrors might max out at 50 rpm's and big mirrors probably no faster than 30 rpm's. When figuring mirrors, I might want to run as low as 3 or 4 rpm's for delicate work. But for rough parabolization, using something between 6 and 10 rpm's is more efficient. With my VFD, gearbox and three-phase motor, I just dial up the speed I want. A pulley system would not be suitable at all for the work that I do. On your suggestion to use a heavy-duty stepper motor instead of my three-phase induction motor... Let's say I'm running a 10-pound turntable with an 80-pound mirror and a 20-pound polishing tool. Plus, I need to add a 10-pound weight to speed up the polishing. So my stack weighs 120 pounds, and quite a bit of the weight is offset and not balanced around the pivot point of the turntable. And during polishing, there is a considerable amount of friction between the polisher and the mirror. Do you have in mind a stepper that could drive that amount of weight and frictional load? The closest I've come to your thought is when I bought a big ClearPath servo motor for use on one of my machines. That motor delivers up to 4600 oz-in of torque, but it cost me over $800. Worth it, as we can develop amazing software to control the motor for all sorts of great custom performance features. Joe, I don't know what "most knowledgeable people would do" but I know my motor is a very economical solution to my specific needs, and I am very, very happy with the flexibility and performance.
Sorry I did not realize you needed that precise a speed for grinding mirrors. I just went through the same issues of having to control an AC motor and, in hindsight, I regret not taking my friend up on his offer of a DC motor which he suggested "could turn a house" for $75. I just decided to go with pulleys and my 3D printer is taking care of that. I'm not putting the sort of loads on my machine as you are though. AC motors are a real pain for variable speed. So, if you don't mind me asking, how much did all of this set you back ? If i ever thought of using a stepper, i would use a worm gear and they can produce a fair amount of torque as well as buffer out the steps. A worm would break it down to a crawl though, requiring the stepper to have to run probably beyond it's rated RPM max.
@@SmeeUncleJoe "AC motors are a real pain for variable speed." Not so much if they're three phase like used in this video. You can typically get a used 3-phase motor for $40-60 (all kinds from 250W - 1.5kW) and a used VFD to control them for maybe another $60-80. That said, most of the articles I've read recommend only going +-20% of the rated speed after which you could potentially overheat the windings, like AnotherGlenn above commented, but, as Gordon replied, in practice this didn't happen for him. Probably depends on your specific requirements, air temp, loads, etc.
@@perspectivex I'm interested to find deals like that, if I had that need. I've never seen that equipment for that cheap. The thing is shipping too. I'm up in Canada. I just don't understand why a person would not reach for a dc motor for applications like this but the OP said he needs that kind of horsepower and I'm not going to second guess him on that. People are giving away treadmills and if a motor and drive from one can easily move a .......... salad dodger ... to jog, I'd think it could handle turning a glass blank with a loaded grinding tool on it.
@@SmeeUncleJoe I don't know if you've tried setting up automated searches on ebay and any other used goods sites that are popular where you are but if you do that I would think that within a few months a cheaper motor would pop up. I tend to get really good deals just because I have searches running for a year or more. Obviously if you need it right away that doesn't work. I don't think there's too much wrong with a DC motor but a far as I understand it they are more expensive for the same power and you might need a special controller. I think treadmill motors might work fine and even though they might be way more expensive new if you salvage one from a machine then it's a big win. Jeremey Fielding does several videos all about motor types and tradeoffs with teardowns. They're very informative; ua-cam.com/video/ASywVBU0ZwE/v-deo.html "How To Wire A Large DC Motor And Control The Speed; Treadmill Motors and Universal Motors 019", and ua-cam.com/video/CeF1I18DhNc/v-deo.html "Building A Variable DC Power Supply From Treadmill Parts: 054", among several others. At least one guy made a mirror grinding machine with one, "The new ones I'm building for up to 28" use surplussed DC treadmill motors run by a Variac (AC auto-transfomer) feeding a 25 amp bridge diode for 0-40rpm at 50v or so... I figure it makes around 3/4 HP there." www.cloudynights.com/topic/399497-type-of-motor-to-grind