Hand Held Tachometer

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Hand Held Tachometer

Post by germaneighter » Thu Apr 18, 2019 2:09 pm

Has anyone used a hand held digital tachometer for setting mill speed? If so, can you supply any feedback?

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Re: Hand Held Tachometer

Post by GlennW » Thu Apr 18, 2019 3:26 pm

I use one for setting spindle speed for CNC tapping using a floating tap holder. Works great!

Operating machines is perfectly safe......until you forget how dangerous it really is!

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Re: Hand Held Tachometer

Post by warmstrong1955 » Thu Apr 18, 2019 3:49 pm

I have a couple....used 'em on a kazillion diesel engines, and even some gas-burners and electric driven things.
Only used one on my lathe one time, to adjust the knob to match the RPM dial, and on the mill, to see how accurate the dial on it really is....

Regardless....they are accurate critters, so if you need to adjust the RPM to a RPM or two, a good and easy way to go.

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Re: Hand Held Tachometer

Post by BadDog » Thu Apr 18, 2019 4:54 pm

They make contact and non-contact varieties. Most contact are mechanical, all non-contact are electronic. The former may provide direct SFPM measure and can work applied to the end of a shaft, the latter require a distinct optical reference (usually reflective tape) along the circumference (or at least sufficiently off access of rotation depending on device resolution).

I have both varieties, and have used them exactly as Bill describes. And some folks have permanently mounted them (usually non-contact) to provide day-to-day reference. But I wouldn't want depend on that exclusively. Like bill suggested, just use it to adjust the mechanical dial to be as close as possible, make a chart for a cone-pulley setup, or come up with an adjustment factor if otherwise not adjustable.

For example, when I got my Roll-In Diemaster vertical bandsaw, it has a feedback mechanical dial that gives approximate speed based on reeves drive pulley position. But the Diesmaster originally came with a slow and/or fast pulley, and the sfpm dial is a 2 rotation (goes around twice from slowest to fastest). I got it from the previous owner who hated it using it to cut cro-mo tubing because "it burns through expansive blades in no time". My first thought, "you are running it too fast" That's what I said to myself, what I said out loud was "I guess I'll have to figure it out. Sold!". Seller didn't have it under power, but when I got it home and turned it on (came with burned up 1" blade), I had to monkey with it to figure out which rotation it was on, and it sure looked WAY fast compared to the dial. No contact tach was handy, so just got RPM x band length, but could have used the SFPM option on my (quite old) contact tach. In any case, it was running nearly 3x stated speed. Based on internal pockets full of aluminum chips, I'm guessing 2 owners back set it up for aluminum. Anyway, I looked at the motor shaft, and see 2 pulleys there, one slid out of position, and a substantially larger driving the main belt. Hmm, looks like the little one should be about right, probably OEM. Swapped around, and the SFPM dial is confirmed to be within a couple percentage points of measured speed (easily accounted by reeves wear). Loving that saw, and no more need for the tach, so battery out and back into the cabinet...
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