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What is this tool? Ebay, OT?

proFeign

Cast Iron
Joined
Oct 2, 2007
Location
Santa Barbara, CA
Maybe OT, but learning about new tools is never OT if you ask me:

http://cgi.ebay.com/Vintage-Brown-S...ryZ92085QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

What the hell is this thing? I want it, but I have a serious tool addiction...

Description from lister:

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I have no clue. It's in great shape and dated 1922. Custom wood box.
 
It’s a tachometer. You stick the end shaft into the centre of a revolving shaft, the dial counts the revolutions, you measure the revolutions against time. Like over 15, 30 or 60 seconds, Best used with a Fob watch in its day. I think the dial was calibrated for 1 minute.

The two holes in the case lid would have been for rubber contact tips. I think one of them would have had a diameter that was calculated to also give feet per minute readings, think flat belts.

(Adding on edit.) We used to have one of those or very similar hanging in the milking shed for when the power went out, and you used to back the tractor up and drive the vacuum pump off the P.T.O. I wouldn’t have seen it in 30 years.

I think the round rubber tip, would have been .318 thou to give you an inch circumference. From that you could work out feet per minute etc.

Regards Phil.

 
I have 1 of those in my toolbox,A kid gave it to me 25 years ago,I just checked my Drill presses with it a month or so ago.Probably used it 20 or so times in my other ,working life.
Gw
 
I have a couple, the sad truth is they work 'ok' but due to all the variances they are not especially accurate. At least not in today's world where we are used to exact or close to exact numbers.
 
Maybe OT, but learning about new tools is never OT if you ask me:

http://cgi.ebay.com/Vintage-Brown-S...ryZ92085QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

What the hell is this thing? I want it, but I have a serious tool addiction...

Description from lister:

s.gif

I have no clue. It's in great shape and dated 1922. Custom wood box.

Hey, I have one like that but I think it's a Starret. I bought some tools from my Father in law and that was among the things I bought. I thought it didn't work because it kept spinning, but reading here I see it is supposed to, and it's not going to give a direct reading.
 
I would suggest "revolution counter" as a better designation than "tachometer". A tach, such as you have in an automobile, gives numbers that represent revs per unit time, such as revs per minute. If your car's tachometer, which is usually calibrated in rpm, reads 7500, your engine is spining at 7500 revs per minute. The device you have simply counts revolutions, period, and not revolutions per unit time. If after making a measurement the device reads 15, its sensing head, along with the spinning component you held it against, has revolved 15 times. If your measurement period was 1 minute, then the speed of the component was 15 rpm. If your measurement period was 20 sec, then the speed of the component was 45 rpm.
 








 
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