Author Topic: A cheap tachometer  (Read 1983 times)

Online mklotz

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A cheap tachometer
« on: March 26, 2013, 10:14:20 PM »
It's seldom that one needs to know the rotational speed of the lathe accurately but, if you do and you don't have a tachometer about, here's one way to do it.

Get a length of all-thread and a nut to match it.  Grip the all-thread in the chuck and make two marks on it a convenient distance apart.  Thread the nut on up to one of the marks.  Now, with the lathe running, grasp the nut (use needle-nose pliers) and time how long it takes to move to the next mark.

Given:

d = distance between marks (in)
p = pitch of all-thread (tpi)
t = time for nut to move between marks (sec)

then:

speed (rpm) = 60 * p * d / t
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Regards, Marv


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Online Tennessee Whiskey

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Re: A cheap tachometer
« Reply #1 on: March 26, 2013, 11:15:56 PM »
You don't reckon smarts like that might have come from eating those calf brains and aigs, now do you? I remember before I smelled nitro, burning rubber and perfume, there was a group of us that would work practical problems like that. Now, I enjoy the practical problems so I can try to  remember the rest.

Yo Redneck,
Eric

Offline Chris J

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Re: A cheap tachometer
« Reply #2 on: March 26, 2013, 11:28:41 PM »
It's seldom that one needs to know the rotational speed of the lathe accurately but, if you do and you don't have a tachometer about, here's one way to do it.

Get a length of all-thread and a nut to match it.  Grip the all-thread in the chuck and make two marks on it a convenient distance apart.  Thread the nut on up to one of the marks.  Now, with the lathe running, grasp the nut (use needle-nose pliers) and time how long it takes to move to the next mark.

Given:

d = distance between marks (in)
p = pitch of all-thread (tpi)
t = time for nut to move between marks (sec)

then:

speed (rpm) = 60 * p * d / t

What a great tip, thanks.
Don't believe everything you read on the internet - Abraham Lincoln.