Mrpete222 has one

[jwmay]

Way to go! See, it seems these guys forgot the Cardinal rule of HSM. Which I always thought was “celebrate every posted purchase with hardy approbation and lavish praise.”
I for one, am stoked that you have bought something you wanted, and excited to find out what you learn with it.
Now if’n I wanted to have a permanent mechanical rpm readout, I might scavenge something from the pick a part car yard. But it’s been very seldom I thought knowing the precise rpm would help me. There’s a lot I don’t know though. Maybe your experiment will make me a convert.

 

[Forty Niner]

I saw this on tubalcain's YouTube channel so I had to have one . It's a tachometer , put the rubber plug on a spindle and it tells you the RPM .
I was thinking I would rig this up on a bench mill stand . Those digital read outs offend me .

and
it is cordless!
requires no batteries!

 

[great white]

Probably operates on this principle:

Way to go! See, it seems these guys forgot the Cardinal rule of HSM. Which I always thought was “celebrate every posted purchase with hardy approbation and lavish praise.”
I for one, am stoked that you have bought something you wanted, and excited to find out what you learn with it.
Now if’n I wanted to have a permanent mechanical rpm readout, I might scavenge something from the pick a part car yard. But it’s been very seldom I thought knowing the precise rpm would help me. There’s a lot I don’t know though. Maybe your experiment will make me a convert.

Automotive tachometers are electric. Gas vehicles take the tach signal from the ignition, diesel ones (typically) take signal from the alternator.

Unless you go back to something like 1910 you won’t find a mechanical tach in an autowrecking yard. If you want to try and adapt a mechanical tach, look in motorcycle scrap yard for bikes before the mid 90’s….good luck trying to correct it to be accurate though….

 

[jwmay]

Probably operates on this principle:


Automotive tachometers are electric. Gas vehicles take the tach signal from the ignition, diesel ones (typically) take signal from the alternator.

Unless you go back to something like 1910 you won’t find a mechanical tach in an autowrecking yard. If you want to try and adapt a mechanical tach, look in motorcycle scrap yard for bikes before the mid 90’s….good luck trying to correct it to be accurate though….

That’s good info! I don’t have any interest in doing it anyways.
It’s funny to me though how I told you I don’t know anything about cars without meaning to. Lol

 

[ChazzC]

Mechanical speedometers & tachometers work on the same principle: the rotating shaft is connected to a either permanent magnet which is inside of a metal cup or attached to a metal disk which is located between the poles of a permanent magnet; the cup or magnet (depending on the design) is connected to the indicator needle shaft. Eddy currents drive the indicator shaft which works against a hairspring to show a measure of the induced current. Since the OP referenced Mr. Pete, here's a good video from him showing the guts of a mechanical speedometer. A mechanical tachometer works on the same principle.

I have a beautiful Hasler Chronometric Speed Indicator set from Herman H. Sticht that I picked up somewhere at least 40 years ago:



This works on a different principle: you place the end of the shaft (with an appropriate tip, see attached) against the target rotating spindle and press the red button, which resets the hands & winds a mechanical timer that runs for ~4 seconds when the button is released; while the timer is running, the hands count the number of shaft revolutions based on the internal gearing; when the time runs out, the hands stop and you read the RPM (or FPM if you attached the wheel tip). This Hasler is basically an improved version of the B&S and Starrett Speed Indicators in that it has a built-in timer (and is easier to read!).

I have compared the results of the Hasler with a good quality contact tach and IIRC it was within a couple of percent of the modern instrument. However, the Hasler Chrono is more of a curiosity than anything else, particularly since you can get free apps for your phone that read reflective tape just like a hand-held non-contact tach.

Here is a link with a little more info on the Hasler Chrono.

 

[great white]

I use one of these for small engines:



It’s called a “sirometer”.

Great for engines that don’t have a tach and don’t have a convenient way to hook one up (magneto ignitions mostly), yet need to have the rpm accurately set. Small engines tend to throw rods when over-sped, so you want the max rpm set accurately. Ride on mowers, push mowers, chain saws, weed whackers, pressure washers, etc. It works on anything with an engine.

You can even use it to narrow down vibrations in a vehicle using the "Hz"scale. Little bit of math involved, but you can use it to differentiate between something like tire vibration as opposed to drive-line vibration.

Basically, you drop it on the engine somewhere on a horizontal flat surface, turn the housing to extend the wire until it makes its maximum arc (from the engine vibration) and then read the rpm scale.

Devilishly simple, unbelievably accurate. Its one of those “forgotten” tools from way back when.

Supposed to work on anything with a turning shaft, but I’ve never tried it on anything besides engines, so can’t say how it would work on electric motors, lathes, etc.

Might get you through until you figure out how you want to measure rpm on your own equipment.

I use a simple magnetic pickup and digital gauge on my lathe:





Bracket for the sensor, a magnet stuck on the headstock shaft and a wall wart for power. The rest is just mounting the gauge and running a couple wires. Easy peasy. My rpm gauge is mounted in my speed control box, but you could put it wherever you want with a simple bracket.

Lots of options for measuring rpm….

 

[Weldingrod1]

Reed or tuning fork based vibration tachometer are another non electric solution, but good for a permanent installation.

Sent from my SM-G715A using Tapatalk

 

[great white]

Reed or tuning fork based vibration tachometer are another non electric solution, but good for a permanent installation.

Sent from my SM-G715A using Tapatalk

That's basically what the Sirometer is. It's not really a permanent mount type thing. It's more of a "check it and forget it" type of tool. I'd go more along these lines if I wanted something more permanent:

Only problem will be getting one that reads low enough for the slow speeds often used on a lathe. The electronic ones excel in that range....

 

[pontiac428]

You do realize that the surface speed on the lathe changes with every thousandth of infeed as you work, making high precision RPM readout kind of superfluous. That's why most lathes take the whole range and divide it into something like 12 or 18 steps, and you pick the most suitable one to allow you to work without fussing with it. Lathe speeds literally are either too slow, too fast, and just right. None of this matters to four significant digits.

Edit- and even if it did, what difference does knowing the number make?

 

[great white]

shaft rpm translates to surface speed with a bit of simple math. I simply do the math at starting point and adjust the rpm as needed while working.

Works for me, easy peasy.