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  1. #1
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    Default Those cheap handheld digital laser tachometers - any good for machine tools?

    An eBay search for "laser tachometer" wil bring up a ton of generic handheld devices for $10 to $30. Most of them look the same.

    I was looking through reviews on Amazon for the same thing, and noticed that someone said there that these devices only work well for speeds above 1000rpm.

    (Quite a few reviews too from people receiving defective units, so it seems a bit luck of the draw - but that's another issue)

    Has anyone here used one of these devices on machine tools, to read down to about 40rpm?

    Does it work? Because I'm thinking it would be handy checking spindle/chuck/cutter speeds where I'm too lazy to check what belts I've got on, or the VFD is set off 50Hz.

    But it would be useless if its only reliable above 1000rpm.

    Ian

  2. #2
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    Hi Ian,

    I have these speed displays installed on both my mill and bandsaw and another waiting for use on my lathe.

    http://www.ebay.com.au/itm/0-56-DIGI...87032aa&_uhb=1

    They have proved to be very reliable and stable in operation. Based on my experience with them, they will work over a very wide range of speeds from 1 rpm up to (in my case) 3000 rpm, not that I run anything at 3000 rpm. I just wanted to test it.

    If you do a thread search you will see quite a few others here have used this display with similar results. Probably the biggest constraint on your speed range display will be the sensor. It took me several attempts/experimentation to find a sensor with a fast enough response to read speeds about about 1000 rpm. There are also several different types of sensors, magnetic, photo, induction. I opted for an induction sensor and it has worked well.

    I used a notched disc that has 3 segments and so the sensor would "see" 3 pulses/rev. At 1000 rpm, thats 3000 pulses/min or 50Hz. Some of the induction sensors on ebay don't have a response time much past this. I have found that these induction type sensors work well about 3000 rpm (or 150Hz). Also, be cautious, most of the data of these induction sensors say they have a response time up to 150Hz but 50Hz is more realistic.

    Here's the induction sensor I have used (after some experimentation):

    http://www.ebay.com.au/itm/PL-05N-DC...06da880&_uhb=1

    All up, for under $20 delivered.

    Cheers,

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  3. #3
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    Hi Guys,

    This is a similar device to the one used on a lot of the Chinese mills and lathes. They do require a fairly sharp edge on the input signal pulse to register accurately. The one on my mill uses a ring of holes in a thin steel disk with a slotted optical detector.
    Its main issue is that it is sensitive to electrical interference from any nearby source. Mainly the mill's drive motor and its electronics.
    Though just turning on a florescent light causes the display on mine to crash now and again.
    Best Regards:
    BaronJ.

  4. #4
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Gunnaduit View Post
    An eBay search for "laser tachometer" wil bring up a ton of generic handheld devices for $10 to $30. Most of them look the same. . . . .
    I bought one of those units about 8 years ago when they cost ~$50 and I and many others have used it many many times since then.
    I cross checked it against a much more expensive unit at work and they agreed with each other to within 1 rpm. I also compared both to a mechanical tacho and they agreed to within the limit of reading of the mechanical tacho.

    Most people that claim they don't work properly don't understand how they work.
    They operate by sensing a change in its laser reflection and most problems arise because rotating shafts often contain a number of possible reflective surfaces. One guy I loaned it to had problems but it turned out he was trying to use it without the supplied reflective tape, when used the tape it worked fine. These units also can't be used too close or too far from a shaft. Occasionally I do get an odd reading (usually too high) but its nearly always due to a reflection. If you have an idea what the shaft speed is in the first place that is handy or you can reduce refections by blacken the area of rotating shaft with black felt marker.

  5. #5
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    Quote Originally Posted by BobL View Post
    I bought one of those units about 8 years ago when they cost ~$50 and I and many others have used it many many times since then.
    I cross checked it against a much more expensive unit at work and they agreed with each other to within 1 rpm. I also compared both to a mechanical tacho and they agreed to within the limit of reading of the mechanical tacho.

    Most people that claim they don't work properly don't understand how they work.
    T.
    Ditto.

    At very low RPM you must give them time to average/calc the speed.

    Also, as they are reflective I often use plain white chalk as a marker and it works fine at close range.

    Worth every cent as far as I'm concerned.

    I always take the battery out when not used as I have heard they can run down otherwise.

    Rob
    The worst that can happen is you will fail.
    But at least you tried.



  6. #6
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    Oops! I should have read your title better. It was regarding HANDHELD OPTICAL tacho's. I have a cheapie one of those too. As Bob says, they can be erratic in the reading if not used under proper conditions. i.e. a shiny shaft etc. What I tend to do is run black insulating tape on the moving part and then put the reflective tape on. If they receive a proper reading, they are fine.

    WRT the previous sensor I was talking about, I also had issues initially with noise from either the motor or VFD and giving an erratic display. I fixed the issue with a basic low pass filter into the input of the display. From memory it was just a 0.1uF cap between the input signal and ground. This fixed the issue and it since has worked extremely well.

    Cheers,

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  7. #7
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    It's looking hopeful then. Another question though:

    I just had a look at my mill's vertical head attachment. It doesn't have any length of exposed shaft to speak of, so if I were to stick the reflective dot onto one face of the hex nut that holds the 3/8" drawbar, would it work, or would the hex corners create spurious readings?

    Perhaps I should blow ~$20 and find out for myself, but I'm a miser.

    PS, Simon the hard-wired (non-handheld) solution looks good too, but if I can get away with having one handheld device for all my machines to get occasional readings, all the better.

    Ian

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    Quote Originally Posted by Gunnaduit View Post
    It's looking hopeful then. Another question though:

    I just had a look at my mill's vertical head attachment. It doesn't have any length of exposed shaft to speak of, so if I were to stick the reflective dot onto one face of the hex nut that holds the 3/8" drawbar, would it work, or would the hex corners create spurious readings?


    Ian
    Highly likely you will get confused/useless readings.

    It would be better to mark the mill shank with black texta and add a chalk mark.

    Rob
    The worst that can happen is you will fail.
    But at least you tried.



  9. #9
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by nearnexus View Post
    Ditto.
    At very low RPM you must give them time to average/calc the speed.
    Also, as they are reflective I often use plain white chalk as a marker and it works fine at close range.
    Worth every cent as far as I'm concerned.
    I always take the battery out when not used as I have heard they can run down otherwise.
    Rob
    I have changed the battery twice in 8 years on mine

  10. #10
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    I would give them my vote too. As I said in another thread, mine just stopped working, but a replacement is on the way. I checked it against my mill going thru the gears and it appeared to be pretty close. I have a Brother labling machine which produced lots of bits of shiny white tape that get cut off. I tried one of these as a reflective strip and it worked. I don't think I will ever run out. Good to know that chalk will work if I do.

    Dean

  11. #11
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Gunnaduit View Post
    It's looking hopeful then. Another question though:

    I just had a look at my mill's vertical head attachment. It doesn't have any length of exposed shaft to speak of, so if I were to stick the reflective dot onto one face of the hex nut that holds the 3/8" drawbar, would it work, or would the hex corners create spurious readings?
    If they create spurious readings then cover it with black fleet marker.

    There is a simple way of identifying if you are getting spurious readings and that us to use one piece of reflective tape and take a reading. Then add another piece of tape to the shaft and you should get double the initial reading. If you get less than a double increase in the reading then it's time to get the black felt marker out.

  12. #12
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    Quote Originally Posted by nearnexus View Post
    It would be better to mark the mill shank with black texta and add a chalk mark.

    Rob
    Yes, right, I was forgetting that it will work with any high-contrast datum.

    Incidentally, being quite behind the times by the looks of all the old hands who already have these, I first saw it when going through the Element14 (Farnell) catalogue - $89. Then looked at Jaycar - $79. Both no-name generic devices that seem to be just the same as the $20 eBay no-name ones. Not even an Anglo-sounding brand name to justify the extra fifty bucks.

    Ian

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    Quote Originally Posted by BobL View Post
    There is a simple way of identifying if you are getting spurious readings and that us to use one piece of reflective tape and take a reading. Then add another piece of tape to the shaft and you should get double the initial reading. If you get less than a double increase in the reading then it's time to get the black felt marker out.
    Bob, nice tip.

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    I actually used mine to check the speed on my pencil air die grinder.

    Did a YT video on it.

    http://www.youtube.com/watch?v=j-2UOSp1Ptc

    Might be of interest.

    Rob
    The worst that can happen is you will fail.
    But at least you tried.



  15. #15
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    Quote Originally Posted by Gunnaduit View Post
    Yes, right, I was forgetting that it will work with any high-contrast datum.

    Incidentally, being quite behind the times by the looks of all the old hands who already have these, I first saw it when going through the Element14 (Farnell) catalogue - $89. Then looked at Jaycar - $79. Both no-name generic devices that seem to be just the same as the $20 eBay no-name ones. Not even an Anglo-sounding brand name to justify the extra fifty bucks.

    Ian
    It just depends on whether you want to help them with paying the rent on their big flash shops etc. As mentioned, I have a replacement on the way. I recieved an email to confirm I was doing the right thing, and it was a problem with the unit, then another email to say a replacement was on the way. See if either of those two retailers will do that, sight unseen? You will probably have to take it back then wait a month while they ponder whether to ..... we'll replace it..../ we'll shaft this one.

    This is not a specific claim for either of those retailers. Just a general impression regarding retailers. I feel it is safer to buy from EBay than most shops.

    Dean

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