Scaling from pictures

[Occasional machinist]

In this video I show the technique that I use when I need to make up parts from drawings or photos. I made up a replacement indexing plunger for one that had been lost some time in the past. The job itself was interesting but the technique I used to get the proportions right will probably be of interest

[Elizabeth Greene]

That's lovely! Thanks very much. I have some basic experience with this in Fusion 360, but your method of pulling the dimensions off the parts diagram is 10/10.

[Occasional machinist]

Not a problem. Sometimes if you need parts for an older machine tool or piece of equipment, this is one of the few ways of getting them

[Toolmaker51]

If found economically, proportioning dividers and/ or a comparable Perry-graf slide rule, provide takeoffs as well.
Another scheme saves drawing in MS Paint, then using those isometric projections to generate the scaling axes. That someone should market isometric graph printing paper in 1 degree increments, ain't gonna happen.
My go-to parallels the demonstration, not having CAD, Paint and SketchUp have worked, but drafting board and related tools remains favorite. Photos are bigger challenge than drawings, picking an object to set scale, sleuthing required.

[Occasional machinist]

... Photos are bigger challenge than drawings, picking an object to set scale, sleuthing required.

Sometimes I will annotate a photo or drawing with multipliers of a 'dimension' on the part, so you get the proportions of the part but without tying it to a particular dimension. Leaves it a bit open until you can find a part, photo or even a feature that you can scale (a hole for an attaching bolt perhaps, or a handle of some sort).

[unmore]

One very interesting trick in this situation is to use Henner Zeller's Augenmass (eyeball measure) https://github.com/hzeller/augenmass.
With it, If you have or can guess one measure on a picture, you can draw quotation lines for other dimensions. It's possible to draw and measure angles as well.

[Occasional machinist]

Angles are tricky. Usually I use the lengths of the sides to work out using trig if they are anything other than 45 degrees as if scales vary on the different axis, getting a number can be tricky. That's where a drawing of what you have scaled helps too, as it provides a useful check of what you have - that is, does it look sensible?