Hand Scraping a Truly Flat Plane (1908) [pdf]

http://www.galleyrack.com/images/artifice/machine-shop/surface-finishing/hand-scraping/engineeringremin00port-pp233-237-img303-307-production-of-an-original-surface-plate.pdf

by rkagerer • 6 years ago

163 95 6 years ago

galleyrack.com

rkagerer• 6 years ago

Same content, but this link might be a little quicker: https://archive.org/details/engineeringremin00port/page/233/...

If you're interested in the topic, here's some more discussion: https://www.practicalmachinist.com/vb/general/possible-make-...

Skilled hand scrapers... can generate plane surfaces accurate to 40 millionts per foot. The same method applied to lapping of glass can generate flats to 1/2 millionth per foot... The average guy working in an open shop careful of cleanliness and uncontrolled heat input to the work will find 0.0005 per foot readily achievable and 0.0002" per foot with a little more care and effort.

HeyLaughingBoy2• 6 years ago

Without even opening that second link I can guess that Forrest Addy chimes in at some point :-)

[edit] haha. That was even his quote :-)

wcunning3• 6 years ago

I got into machine rebuilding after buying a reasonable 1950's machine shop worth of equipment a few years ago when I started in the auto industry after my master's degree. I happened onto a Craigslist ad of a machine rebuilder going out of business near the office and I picked up basically the whole kit -- cast iron surface plates, power and hand scrapers, bluing medium, etc etc. It took another 6 months before I ran into a guy who was willing to teach me to use all that equipment, up near Flint. He spent a whole career doing fitting and repair for a CNC dealer traveling all over the state and a piece of the rest of the midwest. He was just about the nicest guy I've ever done business with, and he supplies equipment and advice to a huge percentage of the Youtube machinist crowd, plus he saved me the couple grand it would have cost to go take one of Rich King's classes.

All in all, this is a great skill that will persist for a long time, longer than you might think, even if modern machines use replaceable linear rails rather than scraped ways. If you feel like taking it up, watch one of the many Youtube videos from Stefan Gotteswinter or Keith Rucker. Look into the equipment, but think about building your own carbide sharpener, scraper and handle.

Blackthorn• 6 years ago

What's the name of his YouTube channel (assuming that's what you meant by supplies advice)?

kalak451• 6 years ago

I assume he is talking about Richard King. I don't think he has his own channel. but as mentioned Stefan Gotteswinter and Keith Rucker both have videos of the scraping skills they learned from him. (Rucker has actually hosted several of King's classes in his workshop)

edit: I clearly misread the end of OP's post. Definitely not talking about Richard King.

wcunning3• 6 years ago

He doesn't have one, but Solid Rock Machine did a tour of his shop a while ago. He mostly supplies advice and equipment through the grapevine and Practical Machinist.

joncrane• 6 years ago

This is fascinating. I don't know all the terminology perfectly, but I get the gist. I love how transparent and ingenious they are.

(BTW did anyone else think of the Rick and Morty episode where Rick builds a "perfectly flat" platform for Morty to experience?)

doomjunky• 6 years ago

I'm familiar the the bubble, Morty. I also dabble in precicion, and if you think you can even approach it with your sad, naked, caveman eyeball and a bubble of f* air, you're the reason this species is a failure, and it makes mis angry!

Experience True Level!

0xff00ffee2• 6 years ago

I read this on a whim and now I'm amazed: I never considered algorithms as part of mechanical engineering. Very clever. And in a pedantic reading of Richard Dawkins, this is the kind of "meme" he was talking about.

Animats2• 6 years ago

I never considered algorithms as part of mechanical engineering.

Oh, yes. Metal work is all about calculating. The classic book is "Machinery's Handbook", published for 105 years. Machinist's toolboxes often have a built-in space for it.

defterGoose3• 6 years ago

The "bible" though, is "Foundations of Mechanical Accuracy" by Moore. Machinery's Handbook is more of a practical reference used in the shop (like when you want to know what a certain spline or thread profile should look like), whereas Foundations is more theoretical.

nohuhu3• 6 years ago

Thanks for submission, a really interesting read! I'm into restoring old woodworking machinery, and hand scraping is one of the methods for truing lathe ways that I've read about. Could possibly be required for the Walker-Turner lathe I'm working on. :)

mauvehaus4• 6 years ago

Also a woodworker here. I have to ask: how bad are the ways on this lathe and how could they get worn? Moving the banjo and tailstock on a wood lathe shouldn't wear the ways the way the routine use of a metal lathe wears the ways.

analog313• 6 years ago

The worst thing is neglect, rust, and accidental damage. In low volume use, e.g. proto shop or home shop, the ways should be virtually eternal. Keep them covered, clean and oiled.

nohuhu3• 6 years ago

I haven't gotten to measuring wear on the ways yet, don't think I'll need to scrape them but that's a possibility. This is a pet project of mine, a barn find that was in a pretty bad shape when I got it: rusty, crusty, with missing parts and undesirable modifications by previous owners. Specifically the ways are pitted from rust; worse in places that were exposed to the elements. I'll have to try and measure the effect of this pitting on tailstock positioning. I don't think banjo positioning is going to be affected, the ways are not that bad. But then there's always the obsession with perfection, so who knows. :)

I have a soft spot for pre-1950 Walker-Turner machinery, their aestetics are off the charts; I'm trying to restore this lathe to its former glory, or even better. Not quite a classic car showroom condition but as close to it as I can get without spending a fortune in time and money. :)

The current stage is painting; turned out it's pretty tricky to spray glossy enamel so it would level out smooth! Especially in our cool and humid coastal climate, paint takes a while to dry and even longer to fully cure so the process is quite challenging. Not to mention the countless hours it took to grind out casting imperfections, apply bondo filler, sand it, etc etc.

I thought I was getting into woodworking but found that restoring machinery is lots of fun in its own right, and nothing compares to the satisfaction of using a well made and beautifully restored vintage tool. Especially when I'm the one who did the restoration. :)

FlyMoreRockets• 6 years ago

One way lathe ways get worn is if the user uses an abrasive wheel to grind without covering and cleaning the ways.

anateus• 6 years ago

Folks who enjoyed this may appreciate Simon Winchester's recent book The Perfectionists, where he covers this method amongst other things. Core to the idea of perfection are machine tools, what we in software often refer to as a toolchain. The way the toolchain revolution allowed us to go from intricate one off clockwork to reliable longitude measurement, better locks, and industrialized machinery parallels compilers, operation systems, etc.

mauvehaus4• 6 years ago

I thought he went rather quickly from some of the earliest processes (boring, for instance) to stuff that's so abstract as to be removed from anybody's practical experience (disregarding metrologists, of course) and then goes farther into philosophical matters than I found interesting.

I would have much more a book that stayed in the realm of machine tools for about half the content, covering the process of bootstrapping precision in the pre-electronic era.

An interesting third quarter could discuss the limits of precision in practical mass manufacturing and the ways we work within tolerances that are economical. The engine block and head of an internal combustion engine have a large and irregularly-shaped mating surface that's subjected to repeated heating and cooling cycles. How flat do they have to be for a gasket to seal them effectively?

The last quarter of the book could cover developments in the era of CNC, and talked about the interplay between electrical components (e.g. stepper motors) and mechanical components (e.g. lead screws, timing belts, etc) and what we gain and lose in using those type of processes. Boring a hole for example, remains more accurate than CNC'ing it on a mill because good control when one x or y approaches zero becomes difficult both mechanically and mathematically.

Anybody interested in this sort of thing might enjoy "How Round is your Circle", by the way.

Ericson2314• 6 years ago

I wish we took as good care of our tools as they did!

NikolaeVarius• 6 years ago

Not flat but similar idea

https://www.cmog.org/article/hale-reflecting-telescope-palom...

Imagine hand grinding telescope lenses

https://www.youtube.com/watch?v=MjUcBWYVF9s

hinkley• 6 years ago

From what I understand, hand-grinding small mirrors is down to process as much as skill. Solid grinding compounds, once they start to wear, end up wearing themselves too. If you keep the pieces moving just so, you can eyeball a rough radius with the grinding material, and it will smooth itself out while smoothing the glass until they mate up.

Basically once you have a wheel with a high precision axle, you can make lots of curves or straight lines.

HeyLaughingBoy2• 6 years ago

Thanks for the reminder.

About 25? years ago I bought the book How to make a Telescope and two six-inch blanks and grinding materials and set off to grind my own mirror. I never finished (it was super boring and really humid in the basement of my rented apartment) and I have no idea where the "blanks" are anymore but now I live in an area well outside of town where I can see the Milky Way with the naked eye if my neighbors turn their lights off so it might not be a bad project to restart.

Bonus: I have the room to build a grinding machine so I don't have to do it all by hand.

CliffStoll• 6 years ago

Today, large telescope mirrors are finished using ion figuring: neutral atoms are shot at the surface of the mirror blank, for a precision ablation of a few angstroms. This works especially well for hexagonal mirror segments, because you can control the surface shape right to the edge of the mirror. Mechanical figuring (using ceramic or glass blanks) has troubles near the edge.

Sharlin• 6 years ago

Hand grinding telescope lenses (well, usually mirrors) is a fairly accessible hobby; you need patience more than anything else. It’s amazing how little technology you need to attain sub-micrometer precision.

DanBC• 6 years ago

I like this video from John Dobson about handmade telescopes, where he builds a complete telescope including hand grinding the mirrors. https://www.youtube.com/watch?v=snz7JJlSZvw

riskneutral• 6 years ago

There's a guy who used to give classes on hand scraping and machine rebuilding https://www.youtube.com/watch?v=TH7tZZdUr2w

paypalcust83• 6 years ago

It's interesting to get more precise and accurate machines out of the ones came before.

These days, if you want to get milling and grinding down to 1 micron without lapping using only your own expertise and some parts from eBay (air bearings and precision-ground slabs):

https://youtu.be/sFrVdoOhu1Q

The creator (Dan Gelbart) demonstrates nitrogen-tight parts without bearings, and claims zero wear or lubrication needs.

#AvEclub

jbay3• 6 years ago

It wasn't nearly so easy. Dan hand-scraped in several surfaces on the lathe; for example the headstock, to get the axis parallel to the ways, and so on.

ryanobjc• 6 years ago

I've been doing woodworking with handtools, and it's amazing what 90 year old tools can do. I bought an old stanley plane in good condition, and was able to start pulling cuttings that are 4/1000" easily. My modern lee valley plane is even easier to set, and I just did a 1/1000" shaving. That means you can surface a piece of wood to 1/1000th of an inch.

This is the kind of accuracy you typically associate with modern CNC machining.

Wood is an interesting medium - it's always in motion so it's in some ways more challenging than working with steel. You can't just machine and glue wood together if you want to make something that'll last for centuries, like old furniture used to. The art is still alive, and I encourage people to check it out!

dekhn5• 6 years ago

I think most people would say, although you might observe such sizes when cutting wood, temperature and humidity will swamp out those precisions within a day or two.

dekhn5• 6 years ago

One of my favorite parts of Feynman's brilliant talk about the limits of minaturizing mechanical devices, "There's plenty of room at the bottom":

"""If, for instance, having made a small lathe with a pantograph, we find its lead screw irregular – more irregular than the large-scale one – we could lap the lead screw against breakable nuts that you can reverse in the usual way back and forth until this lead screw is, at its scale, as accurate as our original lead screws, at our scale.

We can make flats by rubbing unflat surfaces in triplicates together – in three pairs – and the flats then become flatter than the thing you started with. Thus, it is not impossible to improve precision on a small scale by the correct operations. So, when we build this stuff, it is necessary at each step to improve the accuracy of the equipment by working for awhile down there, making accurate lead screws, Johansen blocks, and all the other materials which we use in accurate machine work at the higher level. We have to stop at each level and manufacture all the stuff to go to the next level – a very long and very difficult program. Perhaps you can figure a better way than that to get down to small scale more rapidly."""

Many ideas contributed to the modern process of 5nm lithography, but having flat surface plates whose precision is determined by the correct application of operations rather than an external standard has turned out to be one of the most profound.

Now, of course, you can buy a granite surface place with accuracy exceeding almost anything available 100 years ago, for $30. And there are youtube videos of flat surface aficinados who scrape their own.

Animats2• 6 years ago

Making a precision lead screw is an important step. Maudslay invented the modern metal lathe. His original, from around 1800, is in the Science Museum, London, and it has most of the features of a metal lathe of 1900. Or today.

A screw cutting lathe requires a good lead screw as its reference. Maudslay invented a "screw origination machine"[1], a clever special-purpose device for making a more accurate screw than the one you have. It only cuts soft metal, so the screw it makes is used in a second lathe to make one in hard steel. This is another of the key steps in bootstrapping to precision.

Early precision work was limited to flat things and round things. Take a look at a steam locomotive from around 1900. Every surface that has to be held to a tight tolerance is flat or round. That's because the precision tools of the era were the planer, lathe, and drill. The general purpose milling machine came later.

Incidentally, this is the real reason manholes were round. In the great era of city sewer-building, you could make round metal manhole covers easily, by casting and a quick lathe pass. The ring into which they fit could also be easily finished on a lathe. Making an iron rectangular frame and a lid to fit it would have been a much harder and more expensive job.

[1] https://gracesguide.co.uk/Henry_Maudslay:_Machine_Tools

kazen44• 6 years ago

If you are interested in the history of precision engineering. I can highly recommend the book titled "The Perfectionists: How Precision Engineers Created the Modern World".[1]

It does into detail on how precision manufacturing was created from the beginnings of the industrial revolution until today. The book has some funny anocdotes from history, and despite being quite long i found it easy to read.

[1] https://www.goodreads.com/book/show/35068671-the-perfectioni...

dekhn5• 6 years ago

Some of this is covered in One Good Turn: The Natural History of the Screwdriver and the Screw, which I enjoyed more than The Perfectionists. https://www.amazon.com/gp/product/B00CVR143M/

Circa mid-1960s, this defined precision: https://www.amazon.com/Foundations-mechanical-accuracy-Wayne... (at this level of precision, you need a room-within-a-room climate control, because thermal expansion of objects). That leads down the rathole of "jig borers" for making precisely located holes of precise radius and diamond turning machines which are nice for cutting optics.

SECProto• 6 years ago

Incidentally, this is the real reason manholes were round.

This doesn't pass the sniff test to me. A manhole lid fits loosely in its frame, and is simply cast. The round shape is used ecause that way the lid cannot fall into the hole (frame is a slightly narrower diameter than the lid is in any orientation)

jhallenworld2• 6 years ago

Even today modern precision work is cheaper for round things than other shapes. This is why you will not see internal combustion engines with square pistons / cylinders.

analog313• 6 years ago

There's a lovely article from 1886, written by Henry Rowland, who made the first decent diffraction gratings. He wrote about his process of lapping the screw threads to take out minor local errors. His screw didn't have to do a lot of work, but it had to be damn uniform.

https://en.wikisource.org/wiki/Encyclop%C3%A6dia_Britannica,...

StrictDabbler• 6 years ago

Why are people so obsessed with "the real reason" for round manhole covers?

Manholes are round, or were, so that they wouldn't cave in. Everything in a Victorian sewer is round. The passages are too.

You have a round hole in the ground. You need to put a cover on it. Why would you put a square cover? It's going to be smaller than the hole and restrict access or larger than the hole and waste materials.

That's plenty of reason. There doesn't have to be some aspect of machining or a brain-teaser about square covers falling in when on edge or anything else.

We put square covers on round ducts and vice versa for a bunch of reasons in HVAC today. Aesthetics, ease of making dampers, flow... it's a pain in the neck, but we do it, because something is forcing us to. You need a reason to put a square cover on a round hole.

oyebenny• 6 years ago

This reminds me of that Rick and I'm already seeing where Dr Sanchez shows Morty what absolute level is.

ivankirigin• 6 years ago

Here for this comment.

For those who don't know: https://www.youtube.com/watch?v=IMeain2cvBM

lsllc2• 6 years ago

If you're interested in metal working/machining and like "Dad jokes", check out This Old Tony on YouTube:

https://www.youtube.com/channel/UC5NO8MgTQKHAWXp6z8Xl7yQ

Here's his surface grinder rebuild which includes milling and hand-scraping various surfaces to get them dead flat.

https://www.youtube.com/watch?v=RjwKQCiDgBQ

He's super talented and the videos are fun!

gorgoiler• 6 years ago

dad jokes

”Well this isn’t the freshest mill in the world but I figured if I was going to bite off more than I can chew I might as well go the whole nine yards”

Hah. You weren’t kidding.

jedimastert• 6 years ago

https://www.youtube.com/watch?v=RjwKQCiDgBQ

Oh my goodness, is that what his older videos looked like? He's grown an incredible amount as a storyteller and video producer. Wow

lsllc2• 6 years ago

He really has, his newer stuff is epic! In these dark times, he's kept me quite entertained!

jjoonathan• 6 years ago

You just clicked on a video about making a mostly-square block of metal even more square. (pause) Just saying.

I was hooked from the start!

Prcmaker2• 6 years ago

I get great enjoyment out of Tony, but the dry humour of Mr Pete really does it for me. https://www.youtube.com/channel/UCKLIIdKEpjAnn8E76KP7sQg

tempestn• 6 years ago

This video in Dan Gelbart's 'Building Prototypes' series is a great look at producing highly accurate (flat) surfaces. https://www.youtube.com/watch?v=cwdoUjynpEk

Edit: the scraping technique in this PDF is shown at about 13:00.

cartoonfoxes• 6 years ago

I've done this myself recently, and it's a worthwhile experience if you have the patience for it.

If the short treatise in the OP interests you, I would suggest the book 'Foundations of Mechanical Accuracy', PDF easily available though I won't link here. I can also recommend the bible of hand scraping, 'Machine Tool Reconditioning and Applications of Hand Scraping' otherwise known as the Connelley Book.

csours• 6 years ago

Abom79's hand scraping experience: https://www.youtube.com/watch?v=pT5KWvglp_c

rfrey• 6 years ago

People wanting a full treatise on hand scraping should look into Machine Tool Reconditioning by Connelly, available on the used market and the usual other sources. A close runner up for books is Foundations of Mechanical Accuracy by Moore. If you can get a physical copy of the latter, and can afford it, you should - the photographs are magnificent.

Prcmaker2• 6 years ago

While I was studying engineering I worked in a machine shop. In that time I hand scraped or lapped a good few bearings and surfaces. Fast forward six years, researching optical sensing, and I've had to pull those old tricks out of the bag recently. For some reason, of all the skills and techniques I've learned, manual or academic, making a properly flat surface remains the most satisfying.

GaryNumanVevo• 6 years ago

Maybe a home machinist can answer this question.

If I'm on a desert island, I know how to make a flat plane via ABC grinding. How do I make a right angle? Do I decide on a measure, grind 12 gauge blocks to the same height and make a 3-4-5 triangle?

defterGoose3• 6 years ago

Same method essentially. You need three roughly square pieces that are checked for bearing against each other repeatedly, but this time you also have intermediate steps of checking each face for flatness against the master.

SAI_Peregrinus• 6 years ago

You make a box straight edge.

First, you make a surface gauge. A heavy weighted base with a pointer you can vary in height and distance from the base. You scrape/grind the base flat using a surface plate as reference.

You take something you think is roughly square (a long rectangular prism is good), scrape/grind one face flat with one of your surface plates. We'll call this face 1. Then scrape/grind the opposite face flat, and using the surface gauge to check height (position the box with face 1 down on a surface plate. Position the gauge next to it, with the point touching face 2 somewhere. Slide the gauge back and forth: if it gets pushed up face 2 is tilted up in that direction with respect to face 1. If a gap forms under the tip, it's tilted down.) and thereby get it parallel with face 1.

Then scrape/grind two faces which are adjacent to each the first and opposite each other flat. You now have a shape like \_/ or |_/ or such, though with a top parallel to the bottom.

You stick your surface gauge along one side, touching at the base and at some point near the top of that side with the indicating point. You then turn the WIP straight edge box 180 degrees, and see if the other side touches the indicating tip or the base first. The distance from touching both at once tells you how far out of parallel that side is from the first. You then proceed to scrape them both to be a bit more flat and parallel. Then you turn the box onto its top (face 2) and repeat that. Using 180 degree rotations in two dimensions will get you a good square.

Another thing that can be used as a check (if you can draw) is to build a compass and a straightedge. Side 1 of your box is a good straightedge! You can then use basic geometric construction to make a right angle, and can compare any finished box to that angle.

jbay3• 6 years ago

Practically, the fastest and easiest way would be to turn a good cylinder and measure the diameter at several points (or roll on a surface plane) to make sure it's not tapered, because the face will sit square to the sides even if the axis cutting the face is concave.

More fundamentally though, you can use a similar method -- start with a surface plate, and make three almost-90-degree right angles. Label them A, B, and C.

Scrape A and B so they perfectly mate with each other while they sit flat on the surface plate. They might be something like 89 degrees and 91 degrees, so scrape C to be a copy of B, and then mate it with B. From that you can tell if they're both acute or obtuse, do the correction, and repeat.

WalterBright4• 6 years ago

When I was in high school, it was popular among some of the students to make telescope mirrors. The technique of hand-grinding them to incredible perfection was both simple and astounding.

WalterBright4• 6 years ago

I remember one of the "ancient aliens" TV shows back in the 70s which claimed that the precision with which Inca masons fitted stones together was impossible without alien technology.

Then an archaeologist showed how fit two stones together with the same precision in about a half hour, using no tools at all. Just rubbing and banging them together.

I asked my mom once how the Egyptians could have possibly made the pyramids straight. She replied pull a long string tight, that's the reference. Figuring I had her this time, I asked how they could have leveled the pyramid foundation. She said dig a trench and fill it with water. The water level forms the reference.

Mom: 2 Me: 0

Gibbon12• 6 years ago

I remember an interview with an archeologist that studied the Nazca Lines. She said one year she had a grad student who was a farm boy. He showed her how to draw a long straight line by setting up a stick a 1000 feet away and then just walking towards it while dragging a another stick behind him. It was perfectly straight.

It's basically the same as the old draftsman's trick for drawing a straight line.

wrycoder• 6 years ago

What is that trick?

robin_reala• 6 years ago

I remember a theory (and I’ve no idea if it’s archaeologically verified) that the level for the pyramids was formed by building a wall around the general area. You then flood this with water and wait for it to evaporate / leak out. As the water recedes, every time a piece of land emerges get a squad of slaves to dig it down and level it out. Eventually you end up with a flat plain.

WalterBright4• 6 years ago

People also made TV shows proving that the Egyptians had discovered pi because pi was in the ratio between the base and the height, or more likely space aliens built it because pi was improbable for the Egyptians.

Then some wit torpedoed it by pointing out that if you used a measuring wheel of 1 cubit in diameter, and measured out the base using so many rotations of the wheel, and measured out the height in cubits, pi is in the ratio without needing to discover it.

No, I don't know what a cubit is. Don't ask.

aazaa• 6 years ago

Reminds me of this guy, who hand-planes engine cylinder heads using a block of wood, straight edge, sandpaper, and feeler gauges:

https://www.youtube.com/watch?v=1ch8KYiqSNg

freosam• 6 years ago

Whitworth's method of scraping (mentioned in this article) is explained in this 1858 paper:

https://en.wikisource.org/wiki/Miscellaneous_Papers_on_Mecha...

leni536• 6 years ago

Have three planes with curvatures c1, c2 and c3. Scraping 1 against 2 results in curvatures: c1' = (c1-c2)/2 and c2'=(c2-c1)/2 (proof is left as an exercise to the reader). The calculation is similar for scraping 1 against 3 and 2 against three. The three scraping operations define three linear transformations on the curvature vector c=(c1, c2, c3): A, B and C.

The article describes a cyclic permutations of these operations, so the final curvature is (A.B.C)^n*c. The absolute value of the largest eigenvalue of A.B.C determines the efficiency of this procedure, it's 1/sqrt(8). It means that by each cycle the slowest mode decays to its 1/sqrt(8) multiple. By each step it decays by (1/sqrt(8))^(1/3) = 1/sqrt(2) on average.

Question: Is there a more efficient procedure?

205guy• 6 years ago

The YouTube channel oxtoolco has a video showing lapping of surface plates. Not the same as hand scraping, but the principle of using a reference surface is similar, and the master plate looks like the illustrations in this 100-year old document. Plus I think with modern synthetic diamond abrasives, you can directly lap the plates against each other.

Lapping starts at 17:40 (they do surface measurements first): https://youtu.be/EWqThb9Z1jk

I am no machinist, but I like the glimpse into the hobby/profession shown on channels like this and others that comments have mentioned. In the video, the channel owner hires a company to service his stone regency plates, so there is an expert who comes and uses specialized tools to measure and then flatten the plates (and certify them too). You can see and experience the expertise that the guy has with these physical systems, yet it’s just one niche job in a huge engineering tool chain. It really made me think a lot about metal machining and fabrication, and how those rely on fundamental measurements and properties such as flatness.

xtiansimon• 6 years ago

While I find random publications--such as this page from _Audels machinists and tool makers handy book_, page 245 Fig 10 & 11 'Method of shifting belt of a counter shaft drive lathe while running...' [1]--about industrial processes utterly fascinating, this one on the Truly Flat Plane is abstruse.

[1] https://babel.hathitrust.org/cgi/pt?id=wu.89089662951&view=1...

Corvus• 6 years ago

I am reminded of a problem faced by geometers in antiquity of building straightedges; how do you draw a straight line when you have no existing straight line to copy from?

The book “How Round Is Your Circle?” includes some interesting solutions to this problem. https://www.goodreads.com/en/book/show/2449815

Hand Scraping a Truly Flat Plane (1908) [pdf]

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