5 ms·
It's hand scraping all the way. For initial standards, the author recommends just going with the straightest thing you have in your shop, then just scrape away
by q3k 5y ago
It's hand scraping all the way. For initial standards, the author recommends just going with the straightest thing you have in your shop, then just scrape away until things mate well.
The books are light on the theory of precision and accuracy, but I would be surprised if most readers of Gingery books didn't also have a PDF of 'Foundations of Mechanical Accuracy' somewhere :). These days nothing about this process is practical, it's all basically an exercise in bootstrapping.
Duckduckgo for 'gingery lathe' if you're interested in seeing results, people have been building these for decades.
- Turing_Machine 5y agoThe Whitworth Three Plates Method should be on anyone's list of the Greatest Engineering Discoveries of All Time. The fact that you can make a precision flat surface starting without any precision tools is pretty amazing at first glance.
- jacquesm 5y agomelt some metal and float some glass on it. That's a very quick way to get a nice reference surface.
- deleted 5y ago[deleted]
- cellularmitosis 5y agoFloat the glass on molten metal?
- jacquesm 5y agohttps://en.wikipedia.org/wiki/Float_glass https://en.wikipedia.org/wiki/Float_glass
- Turing_Machine 5y agoFloat glass is pretty flat, but I'm not sure regular glass is temperature-stable enough for the task (and of course, it's fragile). Temperature-stable glass (e.g., Pyrex) usually requires a lengthy annealing stage. Granite surface plates are pretty popular, though. Maybe glass would be okay for light duty. Speaking of glass, amateur telescope makers can grind mirrors accurate to within 1/4 wavelength of light, using nothing but abrasive powders and patience, but they start out with a pre-cast and annealed Pyrex blank.
- Turing_Machine 5y agoI do use a piece of float glass on my 3D printer bed, and it works well enough. Maybe I'll see if I can figure out how much it distorts when heated (not enough to cause a noticeable problem with the relatively low-precision stuff I've been making thus far). Some people do use borosilicate glass (like Pyrex) for this, but I've been satisfied so far with a piece of regular float glass window stock I had cut to size at Lowes.
- jacquesm 5y agoThere are glass compositions that are very thermally stable, this is a very well researched area because so many pieces of the science puzzle depend on it.
- jacquesm 5y agoNo, but it can get you a pretty good starting point to make something that is really flat. For instance, three pieces of float glass alternated using successively finer grains will get you insane levels accuracy in a relatively short time. To the point where you'd need a laser interferometer to detect where you still have high spots.
- SAI_Peregrinus 5y agoFloat glass is nowhere near as flat as a hand-scraped cast iron surface plate can get. Smoother, yes, but less flat.
- jacquesm 5y agoIt's a pretty good starting point though, and with a little bit more work and some powder you can get it near perfect.
- carre12345 5y agoWhat do you mean by 'hand scraping'? You know, I've never really thought about it, but I would think that grinding two same-material surfaces together with an abrasive compound would result in flatness if the pressure is even.
- q3k 5y ago(Hand) scraping refers to https://www.youtube.com/watch?v=REeGn4hN1Bg https://www.youtube.com/watch?v=REeGn4hN1Bg . With two surfaces you can still have some bias (convexity/concavity) even though they appear to be relatively flat, you need three surfaces for absolute flatness. See the Whithworth Method described earlier in this topic. If you're interested in this sort of stuff and want a video introduction, see: https://www.youtube.com/watch?v=gNRnrn5DE58 https://www.youtube.com/watch?v=gNRnrn5DE58