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[Shop-talk] Tachometers

Subject: [Shop-talk] Tachometers
From: TR3driver at ca.rr.com (Randall)
Date: Sun, 15 Jan 2012 20:01:00 -0800
References: <073a01ccd0d0$4eaac090$ec0041b0$@rr.com> <003901ccd3e2$c91332d0$5b399870$@cablespeed.com>
> Check e bay for a machinist's tachometer. It is a little 
> device that looks
> like a large key. 

Thanks, Gerald.  I am familiar with those, but using one is somewhat
problematic for me as I don't carry a watch (nor a wall clock in the shop
area).  It also makes me nervous to have my hand near a spinning shaft while
I have to look away at something else.  And I like the idea of being able to
measure surface speed directly, rather than having to do the computation.

Instead, I picked up one of the digital contact types at HF this morning.
In fact, I just came in from measuring all 16 lathe speeds (but haven't
tried to check the numbers for consistency yet).  It seems to work well
enough.  The readings are not rock-solid, but I think that is probably
because the lathe and it's single phase induction motor don't actually hold
a constant speed very well.  The reading got more stable when I laid my hand
on the chuck (to provide a bit of load) and the worst case waver was less
than 1% of the reading.

-- Randall  

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