# What's a speed indicator used for?



## Ebel440 (Oct 1, 2014)

I got an old starrett improved speed indicator number 106 I think. It has no model number but looking in an old catalog that's what it looks like. I have never seen one before and no one at my work knows what it is. What's it used for? Is it just to check rpm on a lathe?


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## Alan Douglas (Oct 1, 2014)

Perhaps it's from the days of overhead line shafts and belts, where there would be no way of knowing the speed except to measure it.


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## dgehricke (Oct 1, 2014)

The 104 and the 107 speed indicators are model numbers from Starrett tools. They were used to measure the speed of machine spindles ,shafts, wheels and other rotating applications. the 104 was good for RPMs up to 2000 rpm and the 107 was good for 5000rpms.
hope this helps.
regards
dgehricke


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## Ebel440 (Oct 1, 2014)

I found the model 106 improved speed indicator in a 1915 catalog and the one I found seems to resemble the 106 the most. It has a patent on the tool from 1897. I saw a 104 for sale the same day and it was a little different.


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## Bill Gruby (Oct 1, 2014)

It is an early form of hand held tachometer. It measures speed in RPM's. 

 "Billy G"


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## Vladymere (Oct 1, 2014)

Knowing the spindle RPM and the diameter of your stock you can then determine the stocks surface feet per minute which is used to determine the depth of cut.




Vlad


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## pebbleworm (Oct 1, 2014)

I have one and it is fun to use.  And definitely the cheapest speed indicator you can find, if not that precise.  I like it.


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## kd4gij (Oct 2, 2014)

I have one. What are thay used for?:thinking: Well thay are fun to play with. Everybody should have one.


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## Ebel440 (Oct 8, 2014)

I played with it a little but didn't try it on my lathe yet. I'm guessing you need to time it for a minute and that's your rpm?


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## kd4gij (Oct 8, 2014)

Yes it is real hi tec. You just need a watch to use it. ATime it for 1 min or a half min to get your RPM's And then turn it back to "0" by hand.:roflmao:


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## pebbleworm (Oct 8, 2014)

It's like taking the pulse of the machine.  If you have a variable speed motor with no tachometer it really is helpful in zeroing in speeds and feeds.  At least for someone who has no claims to being a professional machinist.  If you are dealing with this stuff all day, every day you would have a sense for it.


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## mixdenny (Oct 21, 2014)

They still sell them, they are pretty much unchanged in 100 years. The earlier ones are collectible, here is part of my collection.   Dennis


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## The Liberal Arts Garage (Feb 29, 2016)

You're   Mostly right- most useful in o.h. Belt days. The high- tech guy had a horse
timing watch in a hunting case. Gave mine away as a curiosity. ........BLJHB


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## 4GSR (Feb 29, 2016)

I bought one new in 1978 to use to set the analog tachometers to the motor RPM's on DC motors back then.  The photocell ones they had back then cost over $1000 bucks! Company was too cheap to buy one.  Now, I have one that that is electronic digital, still photocell, but much smaller scale, that I only paid about $35 bucks for.  The Starrett one was half of my paycheck back then, a whopping $75!  Something like that.  I still have it, too.


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## gi_984 (Mar 1, 2016)

I actually picked up one off Craigslist for $20.  I'll eventually get around to checking the actual speeds on some of my machines at different settings.


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