Comments on: Hey, How Fast Is That Spinning?

By: Jereme Green

Jereme Green — Mon, 11 May 2009 15:06:03 +0000

This looks like a great tool to have when you want to check the specs on a motor

By: fred

fred — Sun, 10 May 2009 19:57:08 +0000

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

By: Phil

Phil — Sat, 09 May 2009 05:07:34 +0000

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.

By: james b

james b — Sat, 09 May 2009 04:54:35 +0000

Can somebody explain the mechanics of how it does it regardless of the direction?

By: PandaRapper

PandaRapper — Fri, 08 May 2009 22:34:30 +0000

I have no need for this, but I want one

By: Dustbuster7000

Dustbuster7000 — Fri, 08 May 2009 20:16:41 +0000

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.

By: ToolGuyd

ToolGuyd — Fri, 08 May 2009 17:59:03 +0000

I wonder how accurate these are…

By: KMR

KMR — Fri, 08 May 2009 17:44:47 +0000

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.