Ideal Tachometer

Unlike step pulleys where there are discrete combinations and speeds, Reeves pulleys have a continuous range of speed.  On machines with Reeves you turn a knob until an indicator points at your desired RPM on a tag.  But how do you know if the it is correct?  To determine the speed measure in revolutions per minute (RPM) a tachometer is needed.  I was curious to know if my machines were rotating at the speeds listed on the tags so I started looking for a tachometer.  Sure, I could pick up a cheap digital tachometer from Amazon or I could look for something else.   So, off I went to Ebay where I was able to win an auction( against no one else) for an Ideal Electric Tachometer.  Specifically it is a Model 50-002B made by the Ideal Commutator Dresser Co. of Sycamore, IL.  The Ideal Commutator Dresser Co was a previous name of todays Ideal Industries that still makes electronic equipment.  It looked to be in great shape with the exception of a broken leather handle which didn’t bother me.  Here’s the nice case it came in.

Here’s what’s inside the quasi padded wooden case.  As you can see everything looks great.

Here’s all the parts out of the case.  From left to right on the top row there is the Indicator, Generator, and an extension cord for “Separable” use.  On the bottom row from left to right there is a wheel for measuring feet per minute (FPM) and several rubber tips.

The tachometer requires no batteries.  When the Generator is spun it creates a voltage which moves the needle on the indicator.  The tachometer can be used with the Generator directly attached to the Indicator as shown below or it can be connected with the extension cord.  The Hi/Lo switch changes the range of the Indicator from 0-2500 to 0-5000 RPM.

Here’s a picture of the extension cord hooked up for use in “Separable” mode.

In the box, underneath the Indicator, is a calibration card from the Ideal company.  I’m guessing this is the calibration card that came with the tachometer when it was made.  As you can see it was made some time in 1945 and calibrated in July.  It was calibrated at different speeds in both hi and lo modes.  The instructions state that it is “accurate within plus or minus 1% of the full scale deflection.”  Doing the math reveals this to be true.  All things considered it seems to be a fairly accurate machine.

Speaking of the instructions, here’s a picture of them if you’re interested.  Per #7, I wonder if I could still send it back for service.  I’m guessing no.

Just because it was accurate 67 years ago doesn’t mean it still is of course.  So, to test it I used the motor on my band saw.  Without a load on an electric motor should turn at the rate listed on the motor tag.  In the case of the Century motor on my bandsaw the tag lists 1750 RPM.   Using the tachometer is simple.  You set the switch to the RPM range you expect to be in, or Hi if you don’t know, and then press the rubber tip of the generator to the end of a spinning shaft.  The shafts on most machines have tapered holes in them from the machining process at the factory giving you a good place to put the tip.  Here’s a picture of the tachometer testing the RPM of the Century motor.

Lets take a little closer look at it. Note the tachometer was in Lo mode so the top scale is read.  It looks pretty close to me.  I also tested it in the Hi range with similar results.

Now that I know it works I can use it on my other machines.  Here’s a picture of me testing the speed on my Clausing 15″ drill press.  I’ve set the drill press to 3000 RPM but as you can see the tachometer reads about 300 RPM high.  This is probably caused by the old belt that I have on the machine which has stretched over time.  Changing the speed to 2000 RPM showed 2200 RPM on the tachometer so the drill press speed error seems to get larger at higher speeds.  Perhaps I’ll pick up a new belt at some point and adjust the drill press to turn at the correct speed.

For my outlay of $22 bucks on Ebay I’m happy with the tachometer.  It certainly is better built that the cheapies.    If it has lasted this long and is still accurate I don’t think it’ll suddenly go haywire in the light duty application I use it in.

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3 Responses to Ideal Tachometer

  1. Tim Graydon says:

    Old school, cool!

  2. gary says:

    I’ve got one too, but the generator part is missing-mine was made in 1958
    Any idea where to get a replacement part?

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