Engineer

It depends entirely on what you want to do with the 'line'.
If it's the centre line on a wooden bow stave split from a log, then a rough pencil line following a taut string is adequate.
If it's a part of a jet engine then something created by a CNC machine or laser is probably more appropriate. It's all about context.
A straight line can also just exist virtually by defining it's ends.
KrisDel^TM can supply a huge variety of virtual lines specially coiled for easy shipping.
Del (I like playing with string)

1) Take one piece of string, longer^[1] than the straight line you wish to generate.

2) Apply tension. Do not exceed breaking strain of string. If you're really fussy, do it in zero gravity (free fall would be OK) and under vacuum.

[1] This is to allow the ends of the string to be grabbed/clamped/tied/nailed or otherwise secured.

Draw one line with the alleged straightedge. Turn it over and draw another line more or less coincident with the first.. If the two lines diverge, just split the difference. Take a look first for dings and scratches, and adjust accordingly. Rinse and repeat until results are satisfactory.

This is what I was taught in Metrology 001, and far be it from me to dispute my illustrious professor.

mount laser on ball head of tripod. point at surface the line is to be on.

turn on laser.

place small mark at top of indication on the surface move incrementally.

repeat as needed.

join the dots.

Del was that 'virtual line product' coiled for 'shipping' or for 'shaping?'

Milo

Are you talking about a Euclidian or non-Euclidian straight line? Inertial or non-inertial frame of reference? How many dimensions is the space containing the line? Is the line supposed to be timelike or spacelike? Do you need the entire line, or just a segment of a line?

The intention is to generate a straight line on a flat surface. A compass generates a circle - there's the clue!!!!

I know - I know! A pair of compasses with legs of infinite length!

You hold the straightedge up, pointed away from your eye, and look along its length. You will be able to see if it is straight. If not, hit the shorter side, not at the very edge, with a ball peen hammer to make it stretch a little and so straighten the ruler. Repeat until it is satisfactorily straight.

My metre rule is now 1050mm long with an attractive scalloped edge....where did it all go wrong
Del

A possible new item, then, for KrisDel™ Industries: Fiddlebow Breadknives!

Well, you shouldn't have hit it that hard (too bigga hammer). _Novices....

Every CAD drawing package can draw a perfectly straight line every time. For a hard copy use the print function.

Is this what you were after? I cannot think of any situations that cannot be handled by either a CAD drawing, metal ruler or laser pointer. Are you talking about lining up a staright line with other objects?

Can you please explain your application in a little more depth.

Its actually a wonderful ontological engineering paradox.

How does one intitially"generate" a straight line if one does not have "straight" lines to derive the "straight " from.

I really loved the "Euclidean noneuclidian" comment, it helped me see this as more a thought experiment...

Milo

My mate René says if he thinks it's straight, it must be.
With my arrows I notice if they are bent when I hit full draw...too late then, it's gone.
Sproing................................................. thwack
Del

" It's what happens when the errors ain't straight"

Whenthesteelbarsarentstraight

Milo

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