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Equal-Arm Balance on a Knife Edge, with a Set of Brass Weights

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작성자

Penny

14. 10월 2026

Equal-Arm Balance on a Knife Edge, with a Set of Brass Weights

The oldest weighing machine is a beam with equal arms balanced on a pivot, a pan hanging from each end: put the load in one pan and known weights in the other until the beam lies level. Balances go back to the Fourth Dynasty of Egypt. A hardened knife edge makes it sensitive and a long pointer shows the smallest tilt; the weights are cast in brass and adjusted against each other. The picture: our diagram of the balance, its knife edge, pointer, pans and weights.

중급

Two to three days

안내

Beam and knife edge

File a straight beam from flat tool steel with a hole exactly in the middle and one near each end, the two end holes equally far from the centre. Forge and file a short steel knife edge, harden and temper it, and fit it through the centre hole, edge down. File a long pointer onto the beam.

이 단계의 재료:

공구강 평봉1 개

필요한 도구:

금속용 줄

손 드릴

디지털 캘리퍼스 6인치

대장간 화덕

담금질 통

보안경

Stand and bearing

Make an upright stand of hardwood with a hardened steel V-block on top, shallower than the knife edge, so the beam rocks freely. Mark a zero line behind the pointer.

이 단계의 재료:

경목 오리목2 개

연강 환봉0.3 m

필요한 도구:

금속용 줄

대장간 화덕

담금질 통

Pans

Cut two equal brass discs, dish them slightly, drill three holes in each rim and hang each from an end hole on three equal cords.

이 단계의 재료:

황동판1 개

밀랍 먹인 아마실3 m

필요한 도구:

판금 가위

손 드릴

금속용 줄

Trim to level

With both pans empty, file the heavier side until the pointer rests on zero. Swap the pans and check again: if the pointer moves, the arms are unequal and the end holes need moving.

필요한 도구:

금속용 줄

Cast the weights

Melt brass and cast a row of plain cylinders a little heavy in green sand.

이 단계의 재료:

황동 잉곳2 kg

숯1 as required

주물사5 kg

필요한 도구:

대장간 화덕

내화 점토 도가니

도가니 집게

주형틀(상형과 하형)

용접 장갑

Adjust the weights

Balance the largest weight against a litre of water measured in the cylinder (one kilogram, our reference), filing it down until the beam is level. Make the smaller ones by balancing pairs against a larger one and against each other, filing each to level.

이 단계의 재료:

물1 리터

필요한 도구:

눈금 실린더

금속용 줄

A binary set of weights

Jupyter 노트북 불러오는 중…

Limits

The balance's form and use are as Wikipedia describes; the sizes and the water reference are ours. Water's density changes a little with temperature, so the reference is good to a few parts in a thousand.