Anyone know what this tool is used for?
A friend has had it in his drawer over 20years and we can’t figure it out.
The long shaft rotates and turns the inner dial. The outer dial turns also, slower than the inner.
Whole thing is about length of your hand.
Made by Starrett in USA – www.starrett.com
UPDATE: Answer Found
I received response from email I left with the Starrett people. They sent me a pdf of instructions, some of which I reproduce here:
#104 & #107 SERIES SPEED INDICATORS
The #104 (black body) and the 4107 (nickel body) speed indicators are inexpensive units for checking the RPM’s of a machine spindle, shaft, wheels and similar applications. This is accomplished by placing the point on the end of a shaft and counting the number of revolutions of the dial.
The #104 can be used for up to 200ORPM. When the point is applied to a revolving shaft, the inner disc is held from turning by firmly pressing on the raised knob with the thumb or forefinger. Then by releasing, the pressure at the time the knob on the outer dial coincides with the knob being held, the disc will revolve. Every 100 revolutions of the spindle is counted by feeling the inner knob pass under the thumb or forefinger. Timing the number of revolutions for a minute will give the RPM.
The #107 is similar to the #104, except it can be used for higher speeds because the revolutions are automatically counted up to 5000. The large outer dial has one hundred graduations, each representing one revolution of the spindle. The smaller inner dial has 50 grooved lines on its face, each representing 100 revolutions of the spindle (or one complete turn of the large dial). A spring, finger attached to the case engages with one of the grooved lines of the small dial, preventing the dial from revolving until the large dial makes one complete turn. With each complete turn of the large dial, the knob trips the spring finger and the small dial moves along to the next grooved line, thus showing that 100 revolutions of the spindle have been made. One complete revolution of the small dial indicates 5,000 revolutions of the spindle. These speed indicators were made from before 1900 until approximately 2006.
It would not be possible to date these as there was very little change throughout this time.