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可穿戴设备
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.
中级
Two to three days
说明
1
1
Beam and knife edge
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.
此步骤所需材料：
工具钢扁钢1 个所需工具：
金属锉
手摇钻
6 英寸数显卡尺
铁匠炉
淬火水桶
安全眼镜2
2
Stand and bearing
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.
此步骤所需材料：
硬木条2 个
低碳钢圆棒0.3 m所需工具：
金属锉铁匠炉淬火水桶3
3
Pans
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.
此步骤所需材料：
黄铜板1 个
上蜡亚麻线3 m所需工具：
铁皮剪手摇钻金属锉4
4
Trim to level
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.
所需工具：
金属锉5
5
Cast the weights
Cast the weights
Melt brass and cast a row of plain cylinders a little heavy in green sand.
此步骤所需材料：
黄铜锭2 公斤
木炭1 as required
铸造砂5 公斤所需工具：
铁匠炉
耐火黏土坩埚
坩埚钳
砂型箱（上箱与下箱）
电焊手套6
6
Adjust the weights
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.
此步骤所需材料：
水1 升所需工具：
量筒金属锉7
7
A binary set of weights
A binary set of weights
正在加载 Jupyter 笔记本…
8
8
Limits
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.
材料
9- 1 个占位符
- 2 个占位符
- 0.3 m占位符
- 1 个占位符
- 3 m占位符
- 2 公斤占位符
- 1 as required占位符
- 5 公斤占位符
- 1 升占位符
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