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  • Digital photo tachometer info wanted.

    I'd like to have a tachometer in the shop. Anyone know if this thing looks promissing as a simple means of confirming speed of lathe, mill, dp and belt grinders?
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    Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

    It is true, there is nothing free about freedom, don't be so quick to give it away.

  • #2
    Don't look promising to me.

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      I don't see what you are referring to?
      For many years I used a "Strobatack" (sp?) to measure rotation
      speeds. They take a little care in using but are good. Don't know if
      they even still exist but bear consideration.
      ...lew...

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      • #4
        Originally posted by Your Old Dog
        I'd like to have a tachometer in the shop. Anyone know if this thing looks promissing as a simple means of confirming speed of lathe, mill, dp and belt grinders?
        I don't know about your thing, but I got one of these off ebay ($20 to $30) plus shipping..... I'm happy with it.

        The small picture is the one I got...sturdy case for long-term nonuse


        Last edited by Deja Vu; 01-27-2008, 02:52 PM.
        John M...your (un)usual basement dweller

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        • #5
          I'm making one for my lathe. I'm using a vintage analog amp-meter so it fits in with my vintage lathe

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          • #6
            I picked up two from Princess Auto. I think they were around $60 each. I don't use them very often but they sure are handy for verifying RPM. I have used them on the lathe and mill but I got them primarily for checking rpm on diesel engines. Kinda hard to use an inductive type tach on a diesel.

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            • #7
              If you're in a do-it-yourself mood, this page http://www.jeffree.co.uk/pages/speedmeasurement.html has some good ideas for home-brew tachometers.
              ----------
              Try to make a living, not a killing. -- Utah Phillips
              Don't believe everything you know. -- Bumper sticker
              Everybody is ignorant, only on different subjects. -- Will Rogers
              There are lots of people who mistake their imagination for their memory. - Josh Billings
              Law of Logical Argument - Anything is possible if you don't know what you are talking about.
              Don't own anything you have to feed or paint. - Hood River Blackie

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              • #8
                http://bbs.homeshopmachinist.net/sho...d.php?p=292238

                He's selling on Ebay and has actually referenced this thread. I'm still very happy with the meter and have no qualms recommending him.

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                • #9
                  Here is a sneak preview;

                  This is how I measured the rpm of my new high speed spindle. I'll be posting more in a new thread later.

                  First is a simple IR phototransistor mounted next to the spindle with a regular incandescent bulb shining on the reflective metal. Half the spindle diameter is covered with black electrical tape.



                  That's the cheap part.

                  The other part is a frequency counter.



                  That is the reading in revolutions per SECOND.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    I did the exact same except used a rare earth magnet and a bobbin of wire I wound. My freq meter is lab quality and was picking up 60hz from the bobbin, of course as there's so much of it around the shop, so I clamped the coil with back to back diodes and removed most of the windings. The resulting near square wave worked out fine and it was quite accurate. What it lacked was portability. The intention at the time was to build it into the system permanently, and I bought a small 4-digit tach just for the purpose, but the portable has proved so handy that I dropped the home brew project.

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                    • #11
                      I'm going to use a Hall effect sensor, a rare-earth magnet, and add a thin ferrous toothed gear to the spindle. The gear doesn't engage anything - its purpose is to focus the magnet's field on its points so the Hall sensor can pick it up easier. The more revolutions, the more current measured by the sensor. This is then fed to the amp-meter (ammeter?)

                      The devil is in the details of course.

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                      • #12
                        Here's a couple I've had the opportunity to calibrate.

                        http://www.harborfreight.com/cpi/cta...emnumber=41727

                        http://www.extech.com/instrument/pro...99/461895.html

                        http://www.extech.com/instrument/pro...99/461825.html

                        For inexpensive units, they should be able to give you a better than 0.5% accuracy.
                        No matter where you go, there you are!

                        Hal C.

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                        • #13
                          I've got this unit I picked up out of a junque shoppe for $8:



                          Press the button and one "barrel" lights up like a flashlight, the other holds a photodetector. You need a reflector, and the unit was originally sold with a packet of stick-on dots, but naturally they weren't included- this thing's gotta be 30 to 40 years old. It uses a 3" long 6v battery for pete's sake.

                          Anyway, that parts easy- $1.95 for a reflective stick-on house or mailbox letter at Home Depot and a plain stationery type hole punch, and you have all the stick-on dots you need.



                          You calibrate it by pointing it at a fluorescent light and adjusting the needle to 7200. After that, it's seemed dead on. Works fine, and it's already proven very handy- instead of making a bunch of calculations between the motor and two jackshafts for a bandsaw, I just read the saw tire wheel speed directly, and worked out the SFM from there.

                          Doc.
                          Doc's Machine. (Probably not what you expect.)

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                          • #14
                            Originally posted by Deja Vu
                            I don't know about your thing, but I got one of these off ebay ($20 to $30) plus shipping..... I'm happy with it.

                            The small picture is the one I got...sturdy case for long-term nonuse


                            Thanks Deja Vue, that's the one I meant to post but didn't. Sorry I didn't get back sooner.
                            - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                            Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

                            It is true, there is nothing free about freedom, don't be so quick to give it away.

                            Comment


                            • #15
                              You're welcome...
                              I'd like to have one that has the "contact" feature incorporated as you often can measure without the little reflective tapes to attach.

                              As it is now, after running around and finding all the turning objects on the premises to stick and measure , I've settled to checking the lathe chuck and the variable speed makita router on my homemade table machine. I've got a QC tool holder that protrudes farther than desired and too high a speed introduces vibrations or can loosen the tool from centrifugal forces on the retaining spring .

                              John Meissner
                              Last edited by Deja Vu; 01-28-2008, 09:47 AM.
                              John M...your (un)usual basement dweller

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