allbrit planimeter

[ARACParticipant @arac]

[ARACParticipant @arac]

Hello all…I have purchased a used Allbrit polar planimeter (yes I am from the days of a drafting board and pencils). It does not have the original instruction manual. If any fellow engineer has one will you please give me a copy…of course postage will be provided or if scanned can be sent directly to me. Thanks

[roy entwistleParticipant @royentwistle24699]

I just googled it, instructions are on line

Roy

[Clive FosterParticipant @clivefoster55965]

Arac.

If you get stuck I have one in the loft somewhere which could be dug out in slow time.

Clive

[Bob LambParticipant @boblamb44747]

ARAC – I have one complete with instructions together with the supplementary instruction leaflet. This second leaflet has a calibration chart for the individual numbered planimeter. I have to admit I gave up any hope of trying to use it when I read the example they gave in the instructions…… "Required, setting for 3 chains = 1in. to read in acres. Standard setting from table = 23.89."

Somehow I don't think I will be using this but it is well made and comes in a pretty case!

If you want a copy of the instructions let me know but I doubt if you will get a calibration sheet for your particular model!

Bob

[John Paton 1Participant @johnpaton1]

It makes me feel truly old to say I was trained in using these – it always fascinated me how rotation in a single axis could derive a two dimensional area. It is a very precisely made instrument and a delightful piece of precision engineering. I have kept two for this reason alone!

The planimeter should come with a small rotating arm on a fixed central pad and having a dimple in the arm and a pointer line scribed at the arms outer end which you use to ensure you start and finish its rotation at precisely the same point. The arm would have an area stamped on it being unique to this 'test piece'. You put the pointer of the planimeter in the arm's dimple and rotate the arm of the test piece exactly 360 degrees and this will turn the wheel on the planimeter a certain number of divisions. That can then be related as a proportion to the 'standard area' stamped on the test arm and used to establish your own calibration chart.

If the test piece is missing it would be possible to make your own as it depends only upon a very precise measurement of the distance between the arms central pivot point to the 'dimple' and multiplying this by itself (pi r squared) and then again by Pi (3.1416) to give the test area figure.

The table simply relates that ratio to various drawing scales and settings of the 'elbow joint' of the planimeter along its arm.

The tool is still useful for obtaining areas and perimeter lengths from style plans and maps, but has been largely replaced by digital drawings and computer aided design software which calculate perimeters and areas of complex shaped items with even greater accuracy and far less effort.

[ARACParticipant @arac]

Thank you all for the responses and Bob Lamb for his scanned copy of the operating instructions of the Allbrit.

I am a novice to the forums but now a convert to them. Perhaps a 'loner' no more!!

Steve

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