Stepper Motors -- a back story to my scraper-sharpener project.
While working on my "low speed motor" side of the project, I encountered a problem. When I turned the power supply on, often as not the stepper wouldn't spin -- it would just buzz loudly. This happened for several different steppers, including a new one. So what was going on?
I did figure out that I could get the stepper to turn by giving the diamond disk a good spin with my hand, but wasn't sure why until I read an article written by some college students who designed and built their own stepper motor controller. The controller included speed and acceleration control. They mentioned that a stepper has limitations with regard to acceleration. If requested to accelerate too quickly, the stepper can't follow so it will lose steps.
I think my simple oscillator circuit is the culprit. It immediately starts oscillating, so the stepper is requested to basically instantaneously accelerate. That's not going to happen so it exhibits the ultimate in lost steps -- it loses them ALL and just turns into a noisemaker.
To solve this I am working on a modification to my 555 oscillator that will produce a ramped output frequency. My first attempt using a capacitor on the control pin didn't pan out so back to the drawing board.
I suppose I could replace my oscillator with a microcontroller but that just seems like overkill. But then I could claim I have the beginnings of a CNC sharpening setup <g>.
Monday, February 15, 2016
Sunday, February 14, 2016
Making the tools to make the tools
Recently I've started learning how to scrape metal. The purpose: improve the fit of machine tool surfaces, like milling machine dovetails. Practically speaking, I want to improve the inexpensive tabletop lathe and milling machines I currently own. They are a good illustration of "you get what you pay for". Although I do have to say that I've made useful stuff on them, doing no improvements other than adjusting them. But as I've become a little more proficient on them, some of the shortcomings have started to annoy me. So began an unexpectedly long (still in progress) sequence of getting tools to improve other tools, only to discover that they're not so great, either.
So I found my self in a sort of bootstrap mode. The starting point was a granite surface plate and what turned out to be a very non-flat surface gauge. So, scraping had to start there before I could even begin to work on my mill. But in fact, I had to go back even further. First, about scraping.
The scraping process involves marking the surface of the item you want to improve. A very flat granite surface plate is loaded with blue pigment, and the work is rubbed over the surface plate. The high spots on the work are marked. They are removed using a sharp scraper. Repeat. A gross oversimplification, but that's basically what is done. At the end, you should have a very flat surface. But not necessarily one that is parallel or perpendicular to anything else you care about. To achieve those other things, you need a good dial indicator and a surface gauge to hold it. I got a decent dial indicator, but the cheap surface gauge I bought quickly revealed itself to be insufficient. It rocked when placed on the surface plate, to the tune of about .006" -- impossibly bad for the kind of standards that scraping can achieve. So my first task became clear: fix the surface gauge. Except it really wasn't the first step, as it turned out.
Through a number of false starts I arrived at the _real_ first step I needed to take: build a setup to sharpen tungsten carbide to make proper scrapers. The photos below show what I came up with. And it works.
Photo above shows the diamond lap (charged w14,000 grit diamond), tool support and tool holder. The scraper is held in place with a set screw that is in one of the steel blocks attached to the holder.
I got the diamond disks from a lapidary supply company. I got 150, 320, 600, 1200 and 3000 grit disks, and 14,000 grit diamond powder. I used the back of one of the coarse disks and charged it with the 14,0000 grit. A disposable aluminum loaf pan is used to hold water -- the disk rotates thru the water for lubrication. The 14,000 grit disk was used dry.
Closeup of holder and 3/4" carbide scraper. The left end of the holder is designed to accept brass inserts with different radii. The support has a fence on the end closest to the diamond wheel (shown at the top of the photo). The brass insert is pushed against the fence, so the end of the scraper describes an arc. This is how I ground a known radius on the scraper.
A photo showing my "low speed motor". It's a stepper motor with a driver. The step pulses are generated with a 555 timer-oscillator.
This is a slow-speed setup so there is little chance of heat buildup. The idea was to have a setup that can also be used to touch up HSS tool bits, and maybe the odd knife or two.
This setup worked very well. The scraper now removes metal pretty effortlessly. I'll sharpen my smaller carbide bits with smaller radii so I can use them for the fine work.
Recently I've started learning how to scrape metal. The purpose: improve the fit of machine tool surfaces, like milling machine dovetails. Practically speaking, I want to improve the inexpensive tabletop lathe and milling machines I currently own. They are a good illustration of "you get what you pay for". Although I do have to say that I've made useful stuff on them, doing no improvements other than adjusting them. But as I've become a little more proficient on them, some of the shortcomings have started to annoy me. So began an unexpectedly long (still in progress) sequence of getting tools to improve other tools, only to discover that they're not so great, either.
So I found my self in a sort of bootstrap mode. The starting point was a granite surface plate and what turned out to be a very non-flat surface gauge. So, scraping had to start there before I could even begin to work on my mill. But in fact, I had to go back even further. First, about scraping.
The scraping process involves marking the surface of the item you want to improve. A very flat granite surface plate is loaded with blue pigment, and the work is rubbed over the surface plate. The high spots on the work are marked. They are removed using a sharp scraper. Repeat. A gross oversimplification, but that's basically what is done. At the end, you should have a very flat surface. But not necessarily one that is parallel or perpendicular to anything else you care about. To achieve those other things, you need a good dial indicator and a surface gauge to hold it. I got a decent dial indicator, but the cheap surface gauge I bought quickly revealed itself to be insufficient. It rocked when placed on the surface plate, to the tune of about .006" -- impossibly bad for the kind of standards that scraping can achieve. So my first task became clear: fix the surface gauge. Except it really wasn't the first step, as it turned out.
Through a number of false starts I arrived at the _real_ first step I needed to take: build a setup to sharpen tungsten carbide to make proper scrapers. The photos below show what I came up with. And it works.
I got the diamond disks from a lapidary supply company. I got 150, 320, 600, 1200 and 3000 grit disks, and 14,000 grit diamond powder. I used the back of one of the coarse disks and charged it with the 14,0000 grit. A disposable aluminum loaf pan is used to hold water -- the disk rotates thru the water for lubrication. The 14,000 grit disk was used dry.
This is a slow-speed setup so there is little chance of heat buildup. The idea was to have a setup that can also be used to touch up HSS tool bits, and maybe the odd knife or two.
This setup worked very well. The scraper now removes metal pretty effortlessly. I'll sharpen my smaller carbide bits with smaller radii so I can use them for the fine work.
Sunday, March 29, 2015
Avogadro's number, the Faraday constant and the electron's charge
Avogadro's number: 6.02X10^23 ions per mole. The Faraday constant: 96,500 coulombs per mole. The charge on an electron: 1.6E-19 coulombs per electron.
Why this post? A small illustration. The background is this: A college physics exam, "cheat sheet" allowed. I brought my cheat sheet, but it had an omission that resulted in consternation during the exam. For a particular question, I _needed_ to use the fundamental charge on the electron. Sorry, I don't recall the exact question, maybe because it was over 40 years ago. But I clearly recall the process I used to address this particular problem because I had neglected to write down this fundamental constant on my cheat sheet. Panic! Woe! At least, initially. Then I thought about it. I did have some information that would allow me to calculate the charge of an electron. Yes, I was fairly certain that I knew the value: but I was in a bit of a panic at the time. How to verify? I happened to have two other important constants on my cheat sheet (but I was certain of them anyway). One was Avogadro's number, the number of atoms per mole of a substance: 6.02X10^23. And the other number, Faraday's constant, which gives the number of coulombs ( a measure of charge) per mole. Dividing Faraday's number by Avogadro's number gave me the charge on a single ion AKA electron: 1.6X10-19.
I used the calculation to solve that particular test question.
Why would anyone be interested in Faraday's constant, other than someone with a peculiar memory for odd physical constants?
Two industries come to mind. One is the electroplating industry. If we know the surface area of something we want to plate, and the thickness we wish, we can use Faraday's constant to calculate the current * time needed to get that thickness. Oh, yeah: Q (coulombs) = current * time. Why is this important? What if you're plating something expensive, like silver. Electroplaters made a shitpot of electroplated silver pieces for folks because it was relatively cheap: but they needed to very precisely manufacture the pieces, including the thickness of that precious silver layer...too thick and they lost money, too thin and the pieces wore out too soon. Faraday to the rescue.
Another industry: the infant electric utilities. They needed to know how much electricity they had delivered to each customer. If they diverted a small percentage of the delivered current to an electroplating cell, they could determine the amount of power consumed by weighing the amount of silver that had been plated.
In both cases, capitalism demanded it: and physics delivered.
While it might seem that physics and the real world have significantly parted ways lately, that's far from the truth. The LED light bulb is a great illustration (pun intended) of this. It is a story of many different disciplines. I will likely elaborate on this in another post.
Quiz time. Here's another useful "constant" I use regularly: .301030. What is it? No, it's not found in physics or chemistry.
Why this post? A small illustration. The background is this: A college physics exam, "cheat sheet" allowed. I brought my cheat sheet, but it had an omission that resulted in consternation during the exam. For a particular question, I _needed_ to use the fundamental charge on the electron. Sorry, I don't recall the exact question, maybe because it was over 40 years ago. But I clearly recall the process I used to address this particular problem because I had neglected to write down this fundamental constant on my cheat sheet. Panic! Woe! At least, initially. Then I thought about it. I did have some information that would allow me to calculate the charge of an electron. Yes, I was fairly certain that I knew the value: but I was in a bit of a panic at the time. How to verify? I happened to have two other important constants on my cheat sheet (but I was certain of them anyway). One was Avogadro's number, the number of atoms per mole of a substance: 6.02X10^23. And the other number, Faraday's constant, which gives the number of coulombs ( a measure of charge) per mole. Dividing Faraday's number by Avogadro's number gave me the charge on a single ion AKA electron: 1.6X10-19.
I used the calculation to solve that particular test question.
Why would anyone be interested in Faraday's constant, other than someone with a peculiar memory for odd physical constants?
Two industries come to mind. One is the electroplating industry. If we know the surface area of something we want to plate, and the thickness we wish, we can use Faraday's constant to calculate the current * time needed to get that thickness. Oh, yeah: Q (coulombs) = current * time. Why is this important? What if you're plating something expensive, like silver. Electroplaters made a shitpot of electroplated silver pieces for folks because it was relatively cheap: but they needed to very precisely manufacture the pieces, including the thickness of that precious silver layer...too thick and they lost money, too thin and the pieces wore out too soon. Faraday to the rescue.
Another industry: the infant electric utilities. They needed to know how much electricity they had delivered to each customer. If they diverted a small percentage of the delivered current to an electroplating cell, they could determine the amount of power consumed by weighing the amount of silver that had been plated.
In both cases, capitalism demanded it: and physics delivered.
While it might seem that physics and the real world have significantly parted ways lately, that's far from the truth. The LED light bulb is a great illustration (pun intended) of this. It is a story of many different disciplines. I will likely elaborate on this in another post.
Quiz time. Here's another useful "constant" I use regularly: .301030. What is it? No, it's not found in physics or chemistry.
Kickoff of Dabblers Lair
For some time I've been thinking about a blog that describes my various tech-centric (mostly) activities. Done not in the vein of trumpeting the victories but as a process of taking a concept or thought and making it real. Or analyzing it and concluding it's impractical or impossible.
My interests have a broad range. Here is an incomplete list.
Machining, as a process of learning how to shape metals and plastics accurately, with few-to-none of those "oh s**t" moments when you figure out you just blew several days of machining.
Nitrogen vacancy centers (NV centers) in diamond. An elegant quantum-mechanical system that could find its way into applications like quantum computing, supersensitive magnetometers, MRI, etc. A system that is relatively easy to experiment with (I think), given a few items available off of Ebay, Amazon and Edmund Optics.
Mathematics. Example: I recently have become interested in the mini-Kossel type of 3D printer. It is elegant in its own way, because the XYZ movements are accomplished by combining 3 identical actuator mechanisms. Conventional XYZ printers use an XY table, with all its foibles, and a Z gantry, also with interesting issues. However, mathematical analysis of the Kossel has shown that its resolution depends on the current position of the printer head. I think the specifications shown for Kossel-based 3D printers are best-case and don't necessarily reflect what users will experience.
Chemistry. I ran across a reference to "magnesium oil", which is used as a topical source of dietary magnesium. If you browse the 'Net for health supplements you will find information which suggests that everyone is short of every element under the sun (literally). My interest was picqued because I was not aware of any benign organo-magnesium compounds. A lot of organo-metallic compounds do things like spontaneously combust in air (like diethyl zinc), or are horribly toxic, like methylmercury. So what is magnesium oil? Turns out it is a fairly concentrated solution of magnesium chloride. Applied topically, it is easily absorbed through. Turns out that it is easy to make using table salt (sodium chloride) and epsom salt (magnesium sulfate).
Here's how it is done. Make two saturated solutions of table salt and epsom salt. Mix the "right" volume of each one so each magnesium ion has two chloride ions available to it. This can be done by looking up the solubility constants for each, calculating the molarity of the resultant solutions and....the rest is left as an exercise for the student <heh>. Now throw the combined solution in your freezer and wait a day or so. The magnesium chloride crystallizes out of solution because its solubility greatly decreases at low temperature. Working quickly, strain out the crystals. Voila, magnesium chloride, which can be redissolved & used for "magnesium oil".
And on and on.
MK 3-29-15
My interests have a broad range. Here is an incomplete list.
Machining, as a process of learning how to shape metals and plastics accurately, with few-to-none of those "oh s**t" moments when you figure out you just blew several days of machining.
Nitrogen vacancy centers (NV centers) in diamond. An elegant quantum-mechanical system that could find its way into applications like quantum computing, supersensitive magnetometers, MRI, etc. A system that is relatively easy to experiment with (I think), given a few items available off of Ebay, Amazon and Edmund Optics.
Mathematics. Example: I recently have become interested in the mini-Kossel type of 3D printer. It is elegant in its own way, because the XYZ movements are accomplished by combining 3 identical actuator mechanisms. Conventional XYZ printers use an XY table, with all its foibles, and a Z gantry, also with interesting issues. However, mathematical analysis of the Kossel has shown that its resolution depends on the current position of the printer head. I think the specifications shown for Kossel-based 3D printers are best-case and don't necessarily reflect what users will experience.
Chemistry. I ran across a reference to "magnesium oil", which is used as a topical source of dietary magnesium. If you browse the 'Net for health supplements you will find information which suggests that everyone is short of every element under the sun (literally). My interest was picqued because I was not aware of any benign organo-magnesium compounds. A lot of organo-metallic compounds do things like spontaneously combust in air (like diethyl zinc), or are horribly toxic, like methylmercury. So what is magnesium oil? Turns out it is a fairly concentrated solution of magnesium chloride. Applied topically, it is easily absorbed through. Turns out that it is easy to make using table salt (sodium chloride) and epsom salt (magnesium sulfate).
Here's how it is done. Make two saturated solutions of table salt and epsom salt. Mix the "right" volume of each one so each magnesium ion has two chloride ions available to it. This can be done by looking up the solubility constants for each, calculating the molarity of the resultant solutions and....the rest is left as an exercise for the student <heh>. Now throw the combined solution in your freezer and wait a day or so. The magnesium chloride crystallizes out of solution because its solubility greatly decreases at low temperature. Working quickly, strain out the crystals. Voila, magnesium chloride, which can be redissolved & used for "magnesium oil".
And on and on.
MK 3-29-15
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