Hey, How Fast Is That Spinning?
By Benjamen Johnson
Hold the rubber tip of K-D Tools’ hand-held tachometer to the end of a rotating shaft, and its dial will tell you how fast the shaft is turning, no matter if it’s spinning clockwise or counter-clockwise. The 2-3/4″ diameter and 4-1/4″ long tachometer can measure rotational speeds between 100 and 4,000 RPM.
You can find this handy little tachometer selling for as little as $95. K-D Tools also makes an extension shaft as well as extra flat and pointed tips.
Hand-Held Tachometer [K-D Tools]
Street Pricing [Google]
Via Amazon [What’s This?]
May 8th, 2009 at 11:44 am
Seriously? $95…
You can buy digital laser tachometers for 1/4 o f that price and theyl will read anywhere from 0-9,999 RPM very accurately. Handy for maching work (measure RPM of a spindle, or spinning work piece)… setting snow blower / lawn mower carbs, and just measuring the rate of anything that spins.
May 8th, 2009 at 11:59 am
I wonder how accurate these are…
May 8th, 2009 at 2:16 pm
I used one of these (or one just like it at any rate) on a work site in India for measuring the velocity of conveyor belts. Provided you can keep good contact pressure between the rubber tip and the measured item, they are pretty accurate, certainly good enough for my purpose. We didn’t pay nearly that much for it, but I think KMR’s idea is much better: non-contact, probably as accurate if not more so, no moving parts to get jammed with sand.
May 8th, 2009 at 4:34 pm
I have no need for this, but I want one
May 8th, 2009 at 10:54 pm
Can somebody explain the mechanics of how it does it regardless of the direction?
May 8th, 2009 at 11:07 pm
I’ve had one of these things for about 35 years or more, and it was given to me by someone who had it many years prior, and it has not changed a bit in all that time.
As for how it works, it’s the same as a mechanical speedometer. It uses a spinning magnet to induce eddy currents in an aluminum drum or armature which is attached to the needle via a shaft and held at zero by a spring. The faster the magnet spins inside the drum, the greater the induced electrical eddy currents in the aluminum become and create a drag, overcoming the spring force and moving the pointer to a position calibrated to that specific RPM. It’s bidirectional much the same way as a doorknob, the spring holds the pointer at zero, but unlike single-direction movements, the pointer has no zero stop and is able to spin both ways. The spring will always bring the pointer back to zero.
May 10th, 2009 at 1:57 pm
Not much use for these in my business - but I’ve seem combo devices like the one made by Extech:
http://www.tequipment.net/Extech461995.asp
May 11th, 2009 at 9:06 am
This looks like a great tool to have when you want to check the specs on a motor