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Digital Tachometer

Discussion in 'Tutorials and Tips' started by Emiliano Achaval, Jun 20, 2019.

  1. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Since I upgraded to a new VFD (That's another story!) I do not have the RPM easily available, the vfd is inside a cabinet, the cover has 4 screws. I was curious about the speed I was chasing threads. I want to be able to tell people in Raleigh at what speed I chase threads. Someone recommended this inexpensive tachometer from Amazon. I tried it today. At first, I almost threw it in the garbage can. It was giving me crazy readings. Then I realized the shop light was shining on the shiny surface where I had placed the reflector tape. I added some painters tape, then the reflector on top of that. Instantly better. I was surprised to find out I was chasing at around 500 rpm. A little too fast.
     

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  2. Mark Jundanian

    Mark Jundanian

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    Personally I like a "speedometer".

    What is the gizmo you bought?
     
  3. hockenbery

    hockenbery AAW Advisor Staff Member

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    Alan Batty told me to slow the lathe to where I can see the spindle threads.
    This is around 300 Not as accurate as a tach.

    One time our club was doing some park demos. I was chasing threads on a mini lathe 500 lowest speed.
    I could do it because I knew how but it was way too fast for me to teach a club member.
     
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  4. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    The problem at 500 is that the odds of hitting the back and blowing or shredding threads greatly increases. Great tip about being able to see the spindle threads!
     
  5. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Hello Mark, you can see a picture of the gizmo I got from Amazon on the original post, above. I'm a little confused, what is the difference between the 2? A speedometer sounds like would give you miles per hour, LOL
     
  6. Mark Jundanian

    Mark Jundanian

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    It was a figure of speech. Some turners feel that RPM information is irrelevant. I am in the camp that finds it useful to have some type of readout.
     
  7. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Would Be interesting to find out how many of those turners are chasing threads. I would take a guess and say that you don't if you did, you instantly would appreciate knowing your rpm. Until I started playing with my chasers, I never looked at my speed.
     
  8. Mike Brazeau

    Mike Brazeau

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    I borrowed one of similar design several years ago and made up a chart for my Oneway 2436. It was mostly a curiousity but I have used the chart occasionally. Their are inexpensive digital readouts on Amazon which are driven by a magnet glued somewhere that a transducer can interact with.
     
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  9. Kent Jaffrey

    Kent Jaffrey

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    I just bought that exact tachometer. I got an old variable speed Woodfast lathe with a stuck speed control knob. After I got it unstuck and “working” I wasn’t sure if I was getting the full speed range and whether a half turn was half the maximum speed indicated. So 5 minutes with the meter and I can now know the speed without guessing. Helpful for a newbie until I get a feel for speed.:)
     
  10. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Hello Mike, I'm curious, would a magnet one be more accurate than the one with the tape, also, more of a permanent solution? Do you know the name of it? Thank you and Aloha
     
  11. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I would go with the optical system. Unless the magnetic system has a Hall effect sensor, the magnetic pickup sensitivity is dependent upon rotation speed. The optical sensor is easy to set up (theoretically, at least). :D
     
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  12. Hy Tran

    Hy Tran

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    I have this on my Robust AB:

    https://littlemachineshop.com/products/product_view.php?ProductID=2658&category=

    It's an optical readout mounted on the handwheel shaft (between handwheel and back of the headstock). Black-and-white tape is good enough (or black paint/white paint).

    Have had no issues with dust accumulating on the shaft.

    I would not use the magnet ones, because you're spinning the magnet around at great speed. (There are ways around that, but let's not get too complicated...)
     
  13. Don Wattenhofer

    Don Wattenhofer

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    The permanently mounted tach readout on my cheap grizzly is driven by a magnet mounted into the driven pulley in a manner that dose not allow it to fly off but an optical unit would do just as good a job. I have an optical hand held unit that I had when I was working that I purchased long before Amazon and cheap clones and it never fails to give an accurate reading, even with shiny shafts or bright shop lights.
     
  14. Steven Forrest

    Steven Forrest

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    I got basically the same unit as Emiliano, (and have a Stubby S750 as well). I ran the lathe at each of the numbers on the speed dial for both low speed and high speed pulley sets, wrote them all down on a card, and hung it from the lathe. Whenever I care, I can check. Used the tach for less than an hour, got my money's worth out of it. Close enough for horse shoes.
     
  15. Keith Mombourquette

    Keith Mombourquette

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    Just today I received and installed a hall effect tachometer from Amazon. I put the magnet right on the shaft of my lathe and wrapped it with a couple of layers of packing tape. Works perfectly.

    [​IMG]
     
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  16. William Rogers

    William Rogers

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    Ok, I do have a cheap hand held unit. I bought it years ago when I had my PM 90. Mainly to see the range and if I had the Reeves drive set to optimum speeds. I had a Laguna Revo with digital readout, but to me it was just an “on” light. So I guess I’m saying a digital readout on the lathe is not something I use. I think it is beneficial to have a handheld unit for random checking, but don’t see much advantage to having a readout on the lathe.
     
  17. Jeff Courtman

    Jeff Courtman

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    I've actually ordered the parts to build one - think I've spent $23 bucks all told. https://learn.adafruit.com/pro-trinket-tachometer/overview

    Going to put it on my new Vicmarc! If you know someone who likes to tinker with mirco-controllers should be a snap! I'll let you guys know if I'm sucessful or not.
     
  18. Tom Albrecht

    Tom Albrecht

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    Can you share a couple photos of your setup?
    And more info on the setup/install process?
     
    Last edited: Sep 7, 2019
  19. Mike Johnson

    Mike Johnson

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    Tom,
    There is a documentation article on the link he listed that shows the sensor dimensions and how it is mounted along with the wiring diagram for the sensor to the display. You could easily drill and tap a hole for a mounting screw to hold the sensor or use an adhesive or magnet to adhere a sub-base for the sensor if you don't want to drill into your headstock. 3M makes a self adhesive mounting tape that works well for small sensor mounting and components. The sensor has 24 inch leads which would be long enough for a typical lathe installation, you would have the same options in mounting the digital display.
     
  20. Hy Tran

    Hy Tran

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    Will do, but it'll be a few weeks before I get to it. I'm 3 hrs away from my Robust, and I've got miscellaneous travel.
     
  21. Tom Albrecht

    Tom Albrecht

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    Last edited: Sep 29, 2019
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  22. Tom Albrecht

    Tom Albrecht

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