2D Printed Tachometer For A Lathe

If you ever wanted a reason to have DC lighting pointed at the spinny part of your mill and lathe, [Bill] tells a great story. One day, he noticed the teeth on his lathe chuck would change color – red, then blue, then red. His conclusion was the fluorescent lights above his workbench was flashing, as fluorescent lights normally do.

Imagine if the teeth on [Bill]’s chuck weren’t painted. They would appear stationary. That’s usually a bad thing when one of the risks of using a lathe is ‘descalping.’ Buy an LED or incandescent work light for your shop.

This unique effect of blinking lights got [Bill] thinking, though. Could these fluorescent lights be used as a strobe light? Could it measure the RPM of the lathe?

And so began [Bill]’s quest for a 2D printed lathe tachometer. The first attempt was to wrap a piece of paper printed with evenly space numbers around the chuck. This did not work. The flash from his fluorescent bulb was too long, and the numbers were just a blur. He moved on to a maximum-contrast pattern those of us who had a ‘DJ phase’ might recognize immediately.

By printing out a piece of paper with alternating black and white bands, [Bill] was able to read off the RPM of his chuck with ease. That’s after he realized fluorescent lights blink twice per cycle, or 120 times a second. If you have a 3″ mini-lathe, [Bill] put the relevant files up, ready to be taped to a chuck.

31 thoughts on “2D Printed Tachometer For A Lathe

  1. “Imagine if the teeth on [Bill]’s chuck weren’t painted. They would appear stationary. That’s usually a bad thing when one of the risks of using a lathe is ‘descalping.’” Behave yourself, you’d know if a lathe was on. They aren’t exactly noise free.

    1. In an ambient with other machines, or even after using the lathe for some time your brain stops paying attention to the noise. Your peripheral vision that plays a big party in you body spatial awareness can also be deceived by the strobe effect.

      1. Separately true, but irrelevant facts.

        If you can’t tell if your lathe is running or not, you probably shouldn’t be playing with a lathe or any other power tools. Seriously… people have been using lathes for a very very long time. And they know whether their lathe is running or not. Why would your lathe be running if you are not actively using it? Have people become retarded?

        If suddenly a generation of people cannot determine it, its because the generation has become stupid.

        Make a hack because it is cool (this is cool and useful for speed indication) and stop with the ridiculous justifications for it after the fact.

        1. Not all machine shops are single-user, for a start. Yes, people have known of the problems with fluorescents for years, and there are high-frequency ones available to mitigate strobing (as I have in my ‘shop). To take the “it won’t happen to me because I’m too skilled/clever” view is neither skilful or clever…

          1. “To take the “it won’t happen to me because I’m too skilled/clever” view is neither skilful or clever…”

            And the opposite of that is to excuse your own stupidity.

            I’m sorry but if you don’t know your lathe is running, you are a candidate for a darwin award. Pure and simple. Death will get you eventually.

          2. I wonder how many got a the darwin award for thinking they were too badass to not know if ‘x’ equipment was running… and I’d probably guess death get to those people first too.

        2. I think we should rely more on the word of those who use such tools for real and less on our own opinion. People have been injured for years while working on power tools. Real people, even the clever ones, made real mistakes when they have to judge based on contradictory sensorial information, like their vision saying that the tool is not running while the hum dimmed through muffles telling its not. Thats not theory, thats real life. Regards!

        3. If you’re that cocky, [Justice_099], then you deserve whatever you get when your number comes up. Any electrical/mechanical tool with moving parts should be treated with extreme caution. If, when you are working around such a tool, you remind yourself that “it’s a matter of when, not if”, you’ll be in a far better frame of mind.

          Your attitude betrays a lack of maturity and experience, and anyone with such an attitude would have no place in my shop. At any given moment, you only get one opportunity not to screw up. A lifetime of accumulated moments requires only one moment of inattention to ruin everything. Your words here seem to suggest that you’re fast-tracking toward such a moment.

      2. Everybody is missing the obvious fact here. A fluorescent light does NOT, repeat NOT, behave like a strobe light (where very short bursts of light are produced at regular intervals). Yes, there is a sinusoidal component to a fluorescent light’s output, but there is a large steady component as well. My point is that a fluorescent light will NEVER make a chuck look stationary, even if the frequency is exactly right. Yes, you will see a faint stationary “ghost”, due to the sinusoidal component, but you’re never going to mistake that with a stationary, non-rotating chuck.

        Now, something positive. I once saw a video where this concept was taken to the extreme, and a synchronised strobe light used to illuminate the lathe work, causing it to appear perfectly still. The results were incredible –


        I’d really like to see someone replicate this. I did a lashup once just running a strobe from a signal generator and adjusting the frequency (it wasn’t synced with the spindle) and it worked OK. It was rather frightening to know that the chuck was rotating, but appeared stationary!

        1. THAT WAS INCREDIBLE. One of the most amazing machining videos I’ve ever seen- I never would have thought to use a strobe light like that! This is like X Ray vision on internal boring- incredibly incredibly cool!

          Thank you for posting that!

        2. Thank you. I’m surprised the obvious needed to be pointed out, but apparently it did. I’ll add that a modern electronic ballast has even less sinusoidal component than the old magnetic ones.

          1. “modern” (at least 10 years ago+) electronic ballasts drive the fluroscent tubes in the kHz range from a DC buffer cap, inverter and HV transformer = more or less constant glow & not much 50/60Hz mains hum left in there.

        3. lathe – check; bright led module with modulation input – check; pulse/signal generator with delay – check; parts for an reflected light barrier – check; time to throw it all together and play with it – nope :(

          fun fact: there is a gym named after the company which made the video 10min from here – lvlup for small world

    2. My father used to work as a metalworker in a workshop. In an environment like that there is always a lot of noise and workers share the equipment.

      When his department moved to a new building many years ago, the new workshop had fluorescent lights everywhere. Trust me, the company soon realised that wasn’t such a good idea.

      Sure, perfect discipline makes this a non-issue. But everyone makes mistakes, especially the intern.

    3. My father was a carpenter for 65 years. The only personal accident of note is a kickback with a custom built saw. He also ran a very successful shop for about 30 years before retiring. Employed quite a few people.

      He was deaf since he was 10 so hearing the equipment obviously wasn’t an option. The key to not getting seriously injured was to familiarize himself with ALL of his equipment and to ALWAYS pay attention.

      I would see this as my father’s idea of adding lightbulbs to his equipment. Another clue as to the state of the machine but it shouldn’t be an excuse to be less attentive. Knowing the RPM would be an added bonus I suppose. But father and I never cared for flourescent lights in the shop so…..

      And no… he has never been separated from any of his body parts.

  2. This is brilliance. The fact that he rediscovered something that others already knew does not make it less brilliant.
    He had the kind of mind truly intelligent people have- he saw something with certain unrelated electrical properties,
    and found a way to use them to measure direct mechanical ones, with no prior knowledge.

    I had seen those speed measurement disks before, but never seen one made for a cylinder like this- which I think only he has done. This is immediately practical to people who own a lathe. Always meant to add a tachometer readout to my Taig,
    but this might work just as well for now.

    Cool stuff!

    1. Assuming ordinary 4′ tubes with a magnetic ballast, you’re right. They flash at 120Hz, and when they do they’re slightly bluer. But the conduction period is only a few ms or so, and the yellower phosphor is the primary light source for the rest of the time.

      Benham’s top / Fechner colors are part of how vertebrate visual systems work, and will not happen with a digital camera.

  3. I’ve seen the EPA use light flicker detecting tops as a cheap energy auditing tool. The flicker indicates the presence of a fluorescent light with a low efficiency magnetic ballast. (More energy efficient electronic ballasts flicker too fast to be detected.) The difference in power between the two is only a few watts, so it wasn’t always economical to change out the light fixtures.
    I made a 3D printable model of the top here: http://www.thingiverse.com/thing:593720

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