What is this? (Starrett tool)

[wgander]

Anybody know what this is for? Is a part missing?
I inherited it and can't figure out what it's for. There's an index mark on the edge of the inner disc, next to the raised surface. Turning the knurled, splined end rotates the inner disc. The part with the knurled surface on one end is about an inch long, and there are splines on both ends. That piece may be removable, but it's stuck fast. There's a pinhole (about the diameter of a paper clip) on the bottom edge of the main portion and there's what appears to be a set screw or retaining screw at an angle into the main portion above where the shaft enters it.

[joedw00]

Does it look anything like this. http://www.josephmarc.com/page-64941.html Then if you do a search for Starrett Speed Indicator No. 104 + Box Pat. 1905 (http://www.google.com/search?q=Starrett+Speed+Indicator+No.+104+%2B+Box+ Pat.+1905&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a) you will get a lot if information.

[wgander]

Thanks for the links.
It's a 104 Speed Indicator that measures revolutions, used with a stop watch you can determine RPM.
I'll have to rummage through the tools I saved and see if there are any tips for it, but I don't remember seeing them.

[dave_t]

Here is an explanation http://bbs.homeshopmachinist.net/showthread.php?t=25693

[JPG40504]

Does it look anything like this. http://www.josephmarc.com/page-64941.html Then if you do a search for Starrett Speed Indicator No. 104 + Box Pat. 1905 (http://www.google.com/search?q=Starrett+Speed+Indicator+No.+104+%2B+Box+ Pat.+1905&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a) you will get a lot if information.

This is a good summary of how it works.(from the second link above)

The top one would have a little rubber pointed tip on it that could be held in the center point of a turning shaft such as a line shaft or machine running off a line shaft, a threshing machine drive belt, etc. By timing the number of turns of the little dial in a minute, it gives the revolutions per minute. At 100 RPM it would turn "button to button" once(look on the face at the two little buttons) at 1000 RPM it would turn ten times in a minute, at 2000 rpm it would turn 20 times, etc. You held it in your hand with your thumb on the button--point on the shaft-- and counted the number of times the moving button went under your thumb while holding your pocket watch in your other hand. Of course, you could just watch it, too. But many of these I have seen have the numbers on the dial about wore away from turning under a thumb. The other numbers around the dial are fractions or percents of a turn. I can't see in your picture but many of them have two sets of numbers, on for each direction of the turning shaft. In the book that came with them there is a chart of speeds for number of turns and fractions, etc. Somewhere in all my stuff I have a virtually new one of those in a box. They must have sold a million of them. I think every blacksmith and machinist would have had one, every steam engine operator, etc.

[wgander]

Thanks for the info

[JPG40504]

Thanks for the info

Thanks for the question. Did not know them existed! Still not too old to learn.:D

[heathicus]

Thanks for the question. Did not know them existed! Still not too old to learn.:D

Agreed! I love old tools and that's a pretty neat one!