rod-mill project - "mains" electric motor advice

Hi everyone I have been shown how to do this with power-electronics and "off-the-shelf" gearbox, etc. With all speed-control needed. A friend had made a small welding positioner. Hence adapted it:

• VFD - 1ph-to-3ph v
• 3ph induction motor v
• worm-drive gearbox You turn a knob setting the output Hz. Adequate speed range.

Having seen this - that it works and does everything wanted - will simply do it this way. Have friend's equipment on "unspecified loan' in my car to take home and play with more.

Hi everyone I have been shown how to do this with power-electronics and "off-the-shelf" gearbox, etc. With all speed-control needed. A friend had made a small welding positioner. Hence adapted it:

• VFD - 1ph-to-3ph v
• 3ph induction motor v
• worm-drive gearbox You turn a knob setting the output Hz. Adequate speed range.

Having seen this - that it works and does everything wanted - will simply do it this way. Have friend's equipment on "unspecified loan' in my car to take home and play with more.

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That is an excellent way to learn what works. The potential problems are cost and custom machining. In that instance I'd look up and save the components' data sheets and see how their max power ratings compare to what was needed and what you intend to do. I've been burned by guessing that something was good enough, my sawmill left a trail of broken ball bearing innards until I switched to a more reputable and expensive brand for the blade guides.

I hardly ever find the same device twice as second hand and must decide on the spot if what I found is suitable, which may depend on its power rating. People dispose of what they can't use, typically because they are either inadequate or broken. I tested that contactor for pull-in voltage and contact resistance.

I will go with "off the shelf". Now seen what's needed. Time si too valuable.

• have the thing working (hopefully!) and making inroads here in Cornwall
• free to get on with other things I have to do - would cost me more in what I have not done than I could save not "placing orders" for what is spec'd for the job.

One "blessing". Gearbox must for sure have a torque rating. Derive torque. Found it's gloriously simple - relation of power, torque and revs. P=tau.omega

P=power (Watts) tau = torque (Newton.metres) omega = rotation-rate (radians/s) Latter makes total sense - well it does for me :-) Radian is where a radius is wrapped around the circumference. Very often gives vast simplifications (compared to working in angular Degrees or Revs Per Minute, etc.). Prompted that way, I can easily see from first principles how "P=tau.omega" can be derived, giving total satisfaction in applying it.

So I can look through spec.sheets for "off-the-shelf" gearboxes.

I have a 30:1 gearbox on loan. However, reckon 7:1 would make the drive "synchronous" (if ran motor at mains frequency, would give the right drive speed). Of course you need speed adjustment to make the mill(s) work exactly right - but what you are asking is very achievable - say +-25% - which an induction motor can do no problem. [welding positioner - is so low power draw for small parts that eg. 10% of the mains synchronous speed it is designed for is not a problem] So going to have to get a 7:1 ish gearbox for mill.

Speed control should be wide enough to run rod-mills and ball-mills on the same rollers-on-a-frame, no mechanical changes needed.

I calculated for the "metallurgical" part of the rod-mill - everything which is and is within the "shell" ("drum"):

• 65RPM of shell rotation rate
• 127W of power draw

P=power (Watts) tau = torque (Newton.metres) omega = rotation-rate (radians/s) Latter makes total sense - well it does for me :-) Radian is where a radius is wrapped around the circumference. Very often gives vast simplifications (compared to working in angular Degrees or Revs Per Minute, etc.).

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I took night school classes to keep up with my day job. The analytic geometry teacher gave many practical hints that made working with sines and cosines simple, but in Degrees. For me learning advanced math from night school teachers who used it as a tool in their day jobs was much easier than from those in college who considered it an abstract art form. In night school I aced calculus classes I'd barely squeaked through in college. I was probably correct to take chemistry which I could pass instead of more mathematical electrical engineering. DC isn't bad, AC requires advanced calculus.

Phase modulation for digital radio employs similar trigonometry but in Radians, expressed as a multiple of pi, 2*pi being a full circle. I struggled to quickly mentally convert between 45 degrees and pi/4 etc, also between decibels and voltage, when listening to explanations of what an engineer wanted me to build or interpreting an instrument display.

Electronics keeps the name omega for radians per second but in print substitutes the small 'o' (omicron) which looks like 'w'. Large omega means Ohms. Likewise the square root of -1 became 'j'.

Now that you have refined your estimate, before spending both you might consider if the desired result is worth the available time plus budget.

I had the same decision to make when designing and quoting custom equipment and with collecting my own firewood. When overtime was available my time was more valuable working it than logging. There was enough down time between R&D projects to stay far enough ahead on the wood, plus cutting and handling it substituted for a health club.

I could never correctly estimate the time to complete a new type of project. Cutting corners early just cost more time later. Last summer's sawmill work took twice as long as planned, much of it unexpectedly repairing and upgrading equipment. The "2000 Lb" gantry eventually lifted 3600 Lbs. The driving time to replace locally bought hardware store parts with stronger industrial ones ate up half a day.

Update these many weeks later...

Video on YouTube:

I put in a few trowels of "sharp sand" - image of result here:

What's seen in video is a contraption. Never-the-less, can do a range of valuable tests hopefully - informing the next iteration of the project.

Regards,

Update these many weeks later...

Video on YouTube:

I put in a few trowels of "sharp sand" - image of result here:

What's seen in video is a contraption. Never-the-less, can do a range of valuable tests hopefully - informing the next iteration of the project.

Regards,

--------------------------- Congratulations. Did you learn anything worth sharing about designing and building low budget powered machinery?

Yes

• blag anything and everything you can - gifted or "on unspecified loan"

• have a lot of mates

• volunteer at societies so you meet people and are not floundering alone

• help others, so help comes back to you

• do go out and do other things - take time out - it's amazing how you can bump into people who know about what it is you are doing

• as ever, there's the balance between: think it through, often doing calculations ^ v get tools in your hands, get started, and try what seems possible

• if you face a significant capital cost, think what it's worth to you in a lifetime. Whatever it is is likely to have some use, and "going for it" "opens doors".

Technically:

Speed control is now in power-electronics.

Expanding that: speed control of electric motor powered machines is now using power-electronics using the "inverter" principle. They've "hit the mainstream".

It goes:

"mains" 1ph v VFD (Variable Frequency Drive) - "inverter" VFD v

I find that in places like the Philippines (what "the West" would call "third world") they have been improvising specialised machines for several years - approaching 10 years now - certainly 7 years judging by YouTube videos. The VFD's (Variable Frequency Drives) all look about the same. Probably one source - or a city where all the makers are concentrated using overwhelmingly the same components.

The cost of the VFD's is some fraction of the cost of the motor - less than 1/3rd - typically more like 1/4. Begs the question - why bother with a single-phase motor any more?!?

The ability to "chop" at higher than the input frequency - empirically I found that that implementation of the rod-mill was optimal at 55Hz to the motor. Our mains here is 50Hz... That bit of "headroom" "saved the day". (the device, the VFD, refuses to go above 60Hz output - likely don't want "the heat" from people turning up at hospital with bits of motor embedded in them?)

That's about it. Glad I went for it. On the "in a lifetime" principle. Work came to a stop while international trade re-aligns and I went for this. Other story here for me is that we have got a diamond core drill working at our hobby mine nearby - and there is some chance of that leading to gainful employment. The thing would need a 300HP compressor "at grass", but we can run it in bursts on the air in the air-main acting as a receiver. Has a 20HP (?) air-motor. Enough while we go through the learning curve. So I have had two big themes in this time.

And ... I have taken the time writing to you all, as a thank-you for timely advice and suggestions. I've had a coffee while doing it. I have quite a list of to-do's and missions today.

Best wishes from here in Cornwall, England.

Yes

• blag anything and everything you can - gifted or "on unspecified loan" ...

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Thanks for writing the nice summary.

I've followed that first one almost to excess, at tech-oriented flea markets, second hand dealers who buy auction lots of industrial equipment and local metal fabricators' scrap piles. Last night I visited the local Maker Space and found I had at least one of almost all metalworking machinery and electronic test equipment they did, except for CNC, which I haven't needed because so much of what I make is cut-and-try matching to existing parts.

I should have mentioned these earlier. Sorry, age-tempered CRS.

In my limited experience with 2 VFDs they come with a default maximum output frequency, 50Hz IIRC with mine, which you have to change in the configuration if you want to run faster. The first ABB VFD was changed to 100Hz, the 2nd a Chinese one to 400Hz. RTFM.

This is my experience too.

Joe

At one that is closing I bought what they had in 10TPI Acme taps. Two are over and under 0.500", 0.480" and 0.520". The size doesn't matter if I'm making a replacement shaft, but what would they normally have been used for?

YOu could go a bit faster as a test with everything out of the way, then settle on what you want?

My pleasure. Thanks for the guidance on this and all other matters.

YOu could go a bit faster as a test with everything out of the way, then settle on what you want?

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That's a question to ask the motor manufacturer. More speed gives greater iron loss heating and greater centrifugal force on the rotor assembly components. I haven't yet abused motors; measuring the frequency response of Variacs showed me that they were closely designed for their rated frequency, losses rose and efficiency dropped rapidly above 60Hz, even at low voltage. I had considered using them in speaker crossover networks. Also applying more than the rated voltage to Variacs and transformers increases the iron loss by increasing the magnetic field strength above its design limit. The loss is visible as an increase in no-load current, which is proportional to voltage below the design limit and rises sharply above it.

For example I saw twice the no-load loss in a welding transformer at 130V as at 120V. At 140V 750W out required around 1000W in. 140V could come from a motor speed regulated gasoline generator set to deliver 110V at full load.

A motor's rotation makes it a generator whose voltage output opposes the power supply and thus limits the current to what the load requires. As the load slows the motor it generates less "back" voltage and allows more current, which permits the motor to drive the load, within design limits.

The 220V grinder motor I tested drew 4A, twice the rating, when stopped with

A simple analog current meter is enough to watch for excessive current draw when experimenting. Measuring the power consumed requires a more sophisticated meter that separates "real" from "apparent" power, Watts from Volt-Amps.

The ABB VFD I was using was connected to an inverter rated TEFC motor, like that one you showed in your clip, and rated to operate at up to 2X the nominal speed at 50Hz, it was powering a flat lap for glass and V belt speed reduction to the lap platter. I only had to balance it slightly to have it run smoothly from min to max speed and no drama even at resonant speeds before balancing. Nice feature of the VFD was scaling of the output display so I had it display platter speed rather than motor speed.

The Chinese VFD set to 400Hz was powering a 24k rpm spindle which is what it was supplied for but it came with basic default parameters so it had to be programmed to run up to 24k rather than 3k so I configured it to run from the VFD panel as a basic test of the VFD and spindle, next is to change the settings for external run input and 0-10V speed control.

What happens if you run things faster in your application you'll have to assess with the components you're using.

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Safety factors are usually greater than 1.5x except in aviation. Chain for instance is designed for 4 times the rating, proofed at 2 times. Important structures may use 5x. My old copy of the AISC steel manual gives loading at

The Springsteen concert film on TV is too distracting to continue.

For what it's worth... Compilation of recent events

It's our local scene here in West Cornwall - interest in geology, mining and minerals. All are joint endeavours Projects have been going from strength to strength.

Most recent is separating galena - lead ore - on a shaking table. "My" rod-mill project and the rod-mill working was a necessary link in the chain. I've been asked if the rod-mill is portable - ie. can it be slung in a car and taken to where there's some minerals actions? That is how far it's gone. The answer is yes just about - but nowhere near as much as I'd like it to be portable. The design where the shell rolls as it will on four wheels, two driven - enables the cylindrical shell to be put in the passenger footwell, where it stays put hemmed-in by the small space and balancing the car, while the frame with motor should go in the back - maybe everything else out of the boot (truck) onto the passenger rear seats and the frame with motor in the boot so it is restrained during travel. Else fold-down the rear passenger seats and in it all goes. Obviously - that the mill runs on domestic "mains" easily, within a fraction of what our "mains" can supply (always 3kW at any socket) and could be on the end of a 10's of metres extension lead totally helps.

The one about about the inverter VFD (Variable Frequency Drive) drawing

Best wishes, Rich S