Need help with a tool reading shaft RPM

[nylon4020]

I have a 4020 with a 686 blower on it. It blows alot of snow but only about 15 feet in a big piled row. I have not used other blowers on this 4020 but have used plenty of other blowers and they tossed snow out into a thin covering around 40 feet. I was questioning my shaft rpm. My wifes grandfather gave me a tool that his father had given him that was used to measure the speed of any spinning shaft. They used it on threshing machines.

This tool has printed on it L.S. Starrett Athol Mass USA Pat April 13 1897 It has gradations on the dial that are 0/100 with a nub marker, 10/90, 20/80, 30/70 and etc. The spinning part of the dial has a gradation line and a nub marker. I am assuming that timekeeping is needed to make a reading but I have no idea how to read the tool. The 1.5 inch spinning shaft has a 3 faced point on it that is placed end on into a rotating shaft to spin the dial. I know that I set my pto up at 540 rpm on the instruments and then come down and us the tool on the shaft. But how to read it I don't know. Any help would be appreciated.

John

 

[nylon4020]

Found this picture of it on this link
http://www.libertytoolco.com/pics/2134-3.jpg

 

[nylon4020]

sorry trying a live link see if this works
Pic of tool link I hope

 

[1944bgardner]

There should be a rubber cone on the end that you hold against the shaft, each increment is 1 revolution. One time around with the inner dial is 100. You have to use a watch with a second hand to time it for one minute, to get your RPM's. Hope the picture helps.

 

[rustyfarmall]

(quoted from post at 10:43:14 08/16/10) sorry trying a live link see if this works
Pic of tool link I hope

Here's the picture

It looks very similar to one I have, except mine is a Craftsman.

 

[gtx1967jewison]

some of them are just tachometers with direct read that look like that too.

 

[Green57]

The graduation is depending of the clockwise ou counterclockwise rotation of the shaft. So if your dial rotate clockwise, you use the outside number. If your dial turn counterclockwise, you use the inner dial.

 

[nylon4020]

Hey guys,

Thanks for the info and the pic posting. Neat old tool. I was supprised that a tool of that era is selling for only 8-10 bucks on that website. Nowday it would be made in china and still cost 79.99 and would never live to be 113.

John

 

[JMS/.MN]

That"s the same tool Dad used in the 40s-50s to check shaft speeds on the AC combine- have it now, and found a second one at an auction a few years ago. You do need to watch the second hand on your watch to get the reading. Rubber nub fits into the center drill hole on the shaft. Center drill hole was made as the first step in turning the shaft in the lathe. Brings it to true center in the lathe.