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Filing to a Line: Marking Out, and Knowing When to Stop
A file does not know where to stop. That is the whole problem: the part is right until one stroke too many, and there is no way back.
So the work is done before any filing starts. A line scribed into the metal, not drawn on it; the line left visible rather than filed away; and the discipline of approaching it from the safe side, slowing down as you get close.
This is also where filing stops being a rough operation. A part filed to a scribed line by hand can hold a tenth of a millimetre, which is tighter than most people expect and quite good enough for most of what gets made.
中级
3 hours
说明
1
1
Scribe a line — never draw one
Scribe a line — never draw one
Coat the surface with marking blue, let it dry, then cut the line with a scriber held against a square or a rule. The scriber removes the blue and cuts a fine groove into the metal, so the line is bright, thin and permanent.
A pencil line is about 0.5 mm wide and rubs off; a marker line is wider still and dissolves in cutting oil. Neither can be filed to accurately, because half the width of the line is more than the tolerance you are working to.
Scribe once, firmly. Going over a line repeatedly produces two or three parallel grooves and then you have to decide which one you meant. On soft metal like aluminium or brass a scriber cuts deeply, so a lighter hand is needed.
此步骤所需材料：
蓝色显示剂1 个所需工具：
划针
固定角尺
直尺规2
2
File to the line, not through it
File to the line, not through it
Work until the scribed groove is just being touched along its whole length, and stop there. The finished surface should still show the line, or half of it.
Which half is a decision made before you start. For a part that must fit INTO something, leave the line on — file up to it and no further. For one that something must fit into, take the line off. Deciding halfway through is how a part ends up a millimetre undersize.
Getting the line to be touched evenly along its whole length is the real skill. If it is being reached at one end first, that end is low: ease off there and concentrate the stroke on the high end, which is the cross-filing diagnosis applied to a line instead of a surface.
所需工具：
锉刀（手用锉）
放大目镜
重型台钳3
3
The tolerance a hand can actually hold
The tolerance a hand can actually hold
正在加载 Jupyter 笔记本…
所需工具：
放大目镜
计算器
笔记本
游标卡尺4
4
Saw first, file last
Saw first, file last
Cut close to the line with a hacksaw — about a millimetre outside it — and file only that last millimetre away.
The removal-rate figures in the cross-filing rung make the case: three millimetres off a small face is over an hour of filing, and a hacksaw takes it in under a minute. Filing exists to make a surface true, not to remove stock, and using it for bulk removal is the commonest reason a beginner decides hand tools are hopeless.
Leave enough to clean up the saw marks and the wander — a millimetre is comfortable, half is tight, and sawing exactly to the line means any wander cuts INTO the finished part with nothing left to correct it.
此步骤所需材料：
低碳钢板1 个所需工具：
钢锯锉刀（手用锉）重型台钳
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