Planimeter

[dnalot]

Didn't know these existed now I have one. Is it of any use to a machinist? It came with a lathe mixed in with a bunch of old micrometers and such. Played around with it for a few hours before I figured out what it does. What it does is measure the area of an irregular shape. The round block has a sharp point in the center and acts as an anchor. Now you just trace around the shape you want to measure and then read the dials.

Mark T

 

[jwcnc1911]

That is awesome! I've never seen one of these used. If you ever get into anodizing or electroplating surface area becomes important. Outside of that I've never seen an "area" call-out on a print.

 

[enfieldbullet]

that's amazing! please get more pictures!

sounds like a physical integrating(as in calculus) engine. those are somewhat rare.

 

[mu38&Bg#]

Used by people who worked with maps. The mechanism sounds interesting, I'll have to look up how it works.

 

[thayer]

My father still has the one that I borrowed while in college for a class in yacht design. We used them to generate areas of the hull cross sections which we then integrated to find total displacement, righting moments, etc. Fun to have and know how to use, but with CAD so prevalent I expect they are less practical than a slide rule these days.

Thayer

 

[albertorc19]

Wonderful instrument, it was used to calculate areas in maps and plans. I've just seen one in a pawn shop, they wanted about 100 dollars for it. It has not any use for me but I really like those fine instruments.

 

[RonGinger]

No steam engineer could be without one. You 'took a card' with an indicator, then measured the area of the curve to determine horsepower. You did one on each end of the cylinder to tell if the valve was adjusted right.

I was at the last running of a BIG 3 cylinder rotary sewerage pumping engine years ago and we were taking cards then- that was the only time I have ever actually seen it done.

 

[Tin Falcon]

Yep the area under a curve is power.You can calculate with calculus or get a good estimate with a planimeter. great for calculating the area of a lake or pond on a map.
Tin

 

[jwcnc1911]

I was having tool envy, already bidding on one on eBay.

 

[Mainer]

Someplace I have a writeup of the mathematical theory of their operation. We used planimeters in one of my engineering classes, maybe thermodynamics.

We always used the dial reading as a relative value only. We'd "calibrate" the planimeter by tracing a square of known area on the graph -- maybe a 10x10 block -- and using the resultant dial reading to figure out a scale factor to use when measuring the actual area of interest.

 

[rodw]

I had one of these and used it on maps. I twas built in the 50's and I gave it to a young Surveyor. He said he thought he knew what it was as everything he did was digital and that was over 10 years go. Very cool bit of gear. I always thought of them as being used for cartography, never machining.

 

[Mosey]

Great old tool, you are fortunate to have. Enjoy it.
There is an old thread here that shows old devices like that.
Soon, analog clocks will be turning up at flea markets, and we can explain to the youngins how they worked in the day to tell time. And, handwritten or drawn objects as well.
CAD programs do a nice job of calculating areas under a p-line.
Mosey

 

[rickhann]

Prior to the digital age, it was a common instrument in any Civil Engineering office or public works office that dealt with road construction. It was used to determine the individual areas of roadway cross sections, at usually 50 or 100 hundred foot intervals. Each cross section would be either a cut section or a fill section or a combination of both. Knowing the areas of each section and the distance between sections, the quantities of earth needed to construct a roadway could be determined. Back in the early 60's during the peak of the Interstate road construction boom, I was a construction engineer for the Illinois Highway Dept. When construction on the highways was shut down for the winter, the construction personnel would be reassigned to the design office. We would be given stacks of plan sheets, a planimeter, and told to "buggy" them. Don't know the origin of the term "buggy", but after a few weeks of "buggying" cross sections for 8 hours a day, we would become buggy! Rick

 

[Gedeon Spilett]

An other way to estimate areas is to copy the design onto cardboard, cut out the shape, weigh and compare it with a standard, I did that when I was student !

this one is the planimeter of Oppikofer (1827). The point p follows the perimeter of the curve and the counter V measures the area drawn by p. The clever point is the cone. the x dimension remains linear while the y dimension is coupled with the cone to the counter, hence measuring the product xy.

 

[Mainer]

Here's a picture of the Dietzgen I bought years ago. I think I may have used it once in the past 20 years. It looks to be newer than the K&E that dnalot has, but basically the same thing. It was for sale, used, for $35 and I couldn't resist.

 

[Shopguy]

Very nice example. But as mentioned kind of obsolete in this day of computers.
Haven't seen one of these in years. I recall they were used for calculating cut and fill on road engineering and in my world for calculating the area of pressure volume diagrams in engine testing.

 

[jwcnc1911]

An other way to estimate areas is to copy the design onto cardboard, cut out the shape, weigh and compare it with a standard, I did that when I was student !

this one is the planimeter of Oppikofer (1827). The point p follows the perimeter of the curve and the counter V measures the area drawn by p. The clever point is the cone. the x dimension remains linear while the y dimension is coupled with the cone to the counter, hence measuring the product xy.

Great. Now I gotta make one of these!

 

[hilij]

John from Malta, I agree with RonGinger the planimeter was used to calculate IHP on steam engines after you took a card with the indicator. I do have a Dobie Macinnes indicator still in original box and also a planimeter. The first I bought in a car boot sale the other I bought on Ebay. I would post a photo when my children show me how))

 

[Hopper]

Of course it is of use to a machinist. For impressing your mates no-end when they visit your shop.
Nice piece of kit just to look at and play with!

 

[rickhann]

John from Malta, I agree with RonGinger the planimeter was used to calculate IHP on steam engines after you took a card with the indicator. I do have a Dobie Macinnes indicator still in original box and also a planimeter. The first I bought in a car boot sale the other I bought on Ebay. I would post a photo when my children show me how))

I am a bit confused as to what you are saying. By stating that you agree that the planimeter was used to calculate IHP infers that it is a single use instrument. It is an instrument used to find the approximate area from a scale drawing. Using it to find the indicator diagram area is but one of a myriad of uses for the planimeter. Rick