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"Cen-Tech" Photo Sensor Tachometer?

Discussion in 'Chainsaw' started by max2cam, Mar 8, 2009.

  1. max2cam

    max2cam AboristSite Guru

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    Anyone use Harbor Freight's "Cen-Tech" photo sensor (no wires) tachometers tuning their chainsaws?

    Says that it reads up to 99,000 RPM
    Stores readings
    +/- 0.05% accuracy
    runs on 4 AA batts
    Price: $49.99

    I had a little mishap with my Solo 690 chainsaw the other day and feel the need to get a tachometer so I can accurately tune all of my saws and not just guess them. I wonder if this unit sold by Harbor Freight will do the job okay and if anyone uses one.

    Thanks
     
  2. sloch24

    sloch24 AboristSite Guru

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    Haven't used it, but like many others here, I don't think a photo-tach will do much good with a chainsaw... They need to see something moving. They usually work with a reflective piece of tape.

    In my opinion, an inductive tach is the only option. I have a Tech Tach that I bought from a site sponsor around Christmas.. it works great.

    Just my 2 cents
     
  3. max2cam

    max2cam AboristSite Guru

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    Could you direct me to that sponsor so I can look at the tach you're talking about?

    Thanks!
     
  4. Edge & Engine

    Edge & Engine Addicted to ArboristSite

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  5. max2cam

    max2cam AboristSite Guru

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  6. Edge & Engine

    Edge & Engine Addicted to ArboristSite

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    No. This tach senses the pulses coming from the coil (off the spark plug wire). The photo sensor tach, like sloch24 said, has to have something moving (physically) to sense. Like he said, a piece of reflective tape on the flywheel, or something like that.
     
  7. max2cam

    max2cam AboristSite Guru

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    Got it.

    Thanks for the clarification.
     
  8. sloch24

    sloch24 AboristSite Guru

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  9. BobL

    BobL Addicted to ArboristSite

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    Yep I agree.

    I have both and the photo-tach (bought for another purpose) is a right PITA to use for CS tuning compared to the inductive. The photo tach has to reflect off a reflective patch on rotating component like a clutch so the standard clutch cover has to come off and then you need some kind of plate to retain the B&C. Fortunately my 076 milling saw has a tranparent section in its clutch cover like this.
    [​IMG]
    The laser needs to reflect off the rotating patch attached to the clutch so some kind of jig is needed to hold the phototach in place or a second person to aim the laser at the reflector. It's possible but it is not easy.
     
  10. pokny

    pokny New Member

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    A naive question about the photo tach

    I have a stupid question, but I'll ask it anyway - why can't you measure the rpm at the sprocket? If there is no load on the drive- so the clutch doesn't slip, isn't the rpm the same as the crank rpm? This way you could put a white or reflective spot on the sprocket and measure with a non-contact tach
     
  11. ericjeeper

    ericjeeper Addicted to ArboristSite

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    Running a saw without a bar and chain is a good way to make parts fly. imho
     

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