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# How do you make more accurate tools from less accurate ones? Answered

I was wondering, in a general sense how people make more accurate tools from less accurate ones.

More specifically, I was reading about reprap and it said it was possible to make components of itself from other previous repraps. However, the errors in them would compound and make less and less accurate/precise models. Therefore there would be some limit to how many times it could replicate.

But, for instance. A lathe requires an accurate/precise leadscrew to control x axis motion. Using a lathe it is possible to make another leadscrew however this would be less accurate/precise than the one already on the machine.

So for my true question. How do they make more accurate ones than the previous ones. If all the current lathes in the world are +- 1mm then how would you make the next set of lathes that are more accurate/precise than that without a piece of machinery that originally had better accuracy. (sort of a chicken and egg problem) Is there some type of machine or algorithm or something that allows a machine to make something that is more accurate/precise than itself.

Thanks

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The origins of the screw-cutting lathe for example go back a very long way. Henry Maudsley is credited with a lot of the early work on precision machines. I have read books on how he made the first accurate leadscrews for example, using corkk nuts that straddled multiple threads, and took up the average position of them, increasing precision each time.

Couple with Maudsley's work, you have to look carefully at what Sir Josepth Whitworth, a great pioneer of metrology and engineering did - it is said that, as Whitworth entered engineering, people would talk of a bare 1/16th of an inch (1.6mm) as very good work. By the end of his career, routine measurements, to a precision of 1 millionth of an inch were being achieved.

Making flat surfaces is a key part in the evolution of metrology, and the invention of the the three plate method was important too.

Circular division is a key field, also tied to precision gearing techniques.

It is remarkable just HOW accurate handwork can be. We routinely expect handwork in my field to be < 0.010" without struggling.

Steve

Excellent answer to a question that has tugged at the edges of my imagination for some time now. Thank you for the recommendations of Maudslay and Whitworth, along with the three plate method and circular division.

One trifle though: Henry's last name was Maudslay. Henry Maudsley was a psychiatrist.

The other answers here are very good. You should certainly give careful thought to what their authors have to say.

Krb686 hits on one key point in his post: knowledge. I'll elaborate here to say that this doesn't just refer to knowledge of a specific field, like knowing how best to shape a material and how it will react under certain conditions. When working to build more accurate machinery using less accurate machinery, knowledge of the specific parts you're working on, and the effects of your actions can be essential. A scientist or machinist can do great things with the resources at their command if they know how best to apply those resources.

There are probably many ways in which people throughout history have used less accurate machinery and instruments to produce more accurate machinery and instruments. I can't speak to what DID happen, but I can sketch out how it COULD happen.

1. This might sound like an unhelpful answer, but I promise this point is important later:

The simplest means of achieving accuracy is transference and replication. Need a sufficiently accurate part? Make it on a sufficiently accurate machine. In many cases the output of the machine is less accurate than the machine itself. Special effort is required to do better than this. Many modern machines are delivered from the manufacturer with hardened steel control surfaces that are more accurate than any part the user will ever need to produce with this machine. In these cases the part is "accurate enough", though quite naturally the question does arise: how can we do better if we only have something less accurate than we want to produce?

2. From the first point flows a very important precept: not all accuracy is derived from a more accurate source. Just because your existing machine doesn't produce your desired level of accuracy very easily doesn't mean that it is UNABLE to produce more accurate results. Carefully measuring the results and adjusting the machine can produce more accurate parts than those the machine itself is built from. Wait, you ask, how can we measure more accurately?

3. For measurement, make multiplication work to your advantage, and not against you. Avoid situations where multiplicative and additive effects could lead to compounded errors. Use levers to perform multiplication for you. We've all exerted a small to moderate force on a long lever in order to exert a greater force over a shorter distance. We can invert that idea and use it to make dial indicators. These dial indicators will measure very small differences in part size and translate those differences into much larger, lower force movements of an instrument needle, behind which we will place paper gauge labels with easy to read graduations. Ok, so now we know how inaccurate our parts are, but what can we do about it?

4. We will take our more precise measurements and use them to create more accurate parts than our machine currently uses, through great craftsmanship, trial, and error. We will do this painstakingly, often using shims and very careful manipulation and measurement to achieve what would be relatively simple to do with a more accurate machine, with far less effort and skill required. Our work product will not be easily repeatable using the same equipment, and will often be confined to the endeavors of one machinist or one laboratory. However, over time these efforts will pay off. Our precise work will enable us to make more accurate measurement instruments and more accurate versions of our starting equipment. This more accurate equipment will enable us to more readily repeat the work we did with such great care and craftsmanship, only this time our excellent results will be much easier to achieve. Using such high effort and craftsmanship, we can again achieve greater accuracy than was readily available from our improved equipment. Ok, now we've achieved greater accuracy than was readily available, and we built better machinery than we started with. Now what?

5. Because we can't achieve greater accuracy on our own, we have to make sure our achievements can help others so they can help us. We must now make this more accurate machinery available to everyone. The comparatively primitive machinists who regard 1/16th of an inch as highly accurate need to learn new standards on new machines. We will eventually reach the limits of what can be achieved through purely physical means. Our machines will make optical grinding more accurate and less labor intensive. That change will lead to massive advances in optics, again, the use of multiplication in our favor. The laser will become not only possible, but commonplace. Advances in electronics will become possible. Computer controlled electronics will make great accuracy available at the push of a button, instead of the work of a lifetime.

Someday, the machinist of tomorrow will ponder how anyone could make a machine more accurate using a less accurate machine.

I just leave this here
http://www.totallyscrewedmachineshop.com/documents/FoundationsofMechanicalAccuracy.pdf

I think the answer to this question that is key is that with an inaccurate tool, knowledge, repeated trials, and accounting for errors, more accurate tools can be made. I have always thought about this question myself as well. Think back to cave men days. How did humans as a whole progress from using extremely inaccurate rocks being pounded together to the accuracy of tools today?

Another thing to consider is crossing different areas of science and engineering. Some technological aspects ALLOW for the creation of more accurate tools. It's all about the building blocks. How did humans create the Empire State Building much larger than themselves? Building blocks. How did humans create computers that calculate linearly millions of times faster than themselves and have transistors merely hundreds of atoms in width ? Building blocks.

A Whole sometimes allows for more than the sum of its parts. Also take for example the discovery of the laser. This piece of technology ALLOWED for more accurate tools.

Check out the most perfect sphere ever created, which has rough spots that vary no more than 3 atoms in width.

http://www.newscientist.com/article/dn14229-roundest-objects-in-the-world-created.html

The reprap prints a part for a newer design or upgrade for the reprap or new machine.

i can only answer the question in a rational calculational sense. consider the screw driver not in it's self a complexed machine, but a mere "tool" to utilize in order to complete a more complex task. such as making a machine that would do the screwing instead of you having to screw, once you had the machine made it would most likely if set at the correct mechanical timing could outspeed a person and deliver much more speed and precision than you could with a screwdriver. so in that logical sense a tool could make a more precise version of itself.

It's amazing how often this question comes up in my mind too..
For example, how do you have a flat and square block, without having a reference??
Finally, after a LOT of thinking I came up with a answer for the screw thing, as long as your guiding it from a thread you SHOULD be able to move at a consistent rate.. Think of the way a die moves down a rod to thread it.. It's using it's previous work as a reference and can cut consistently the same distance.
But it is always a question in my head, how dis we ever get to a point where we can achieve such high precision, and consistently??
But I have always marveled at how we have got there, especially since building 2 cnc's and having a intrest in making all my tools myself

I think if you wanted to find out how to create more accurate tools from less accurate ones, a good start would be at the beginning. I'm a huge fan of the book series by Dave Gingery.

His books let you follow development through the industrial revolution so you have a clear path to go from the creation of one tool to another. Hand tools build a foundry, foundry builds the lathe, lathe builds the shaper, shaper builds the milling machine, milling machine builds the drill press, etc.

Following this process, a drill press is (arguably) more precise then hand drilling the same hole. A miter box will give you more accurate cuts then the saw you used to create the box.

I realized that I never mentioned, that Gingery's books are not an analysis, they actually teach you how to create these tools.

Many measuring and layout operations can be self-correcting, or used for self correction, like squaring a square, or straightening a straightedge. Look around this site for examples.

Operator's skill has A LOT to do with what the tool does.

Aside from the changeover from humans to automation, which imo changed the game considerably, I think it all had to do with the accuracy a skilled operator brought to the party, along with standardization of metrics and likely, the clever use of the same principle upon which the slide rule uses... (anyone else have one of those vernier calipers that shows the principle in action?)

And good eyes. There was a time when I could accurately, by sight, tell you to ~.05 mm what a measurement was. Granted, after several stupid accidents with lasers, a severe knock to the head with a 1" thick steel bar, a couple chips in the eye from stones I was working, and the added effect of the aging process, that is a definite *was.

There IS a real method by which it happens. I learned it once, but all I have to fall back on now that the memory has faded is what I wrote above, which is just "logicking", rather than actual delivery of a known method.

The original screw cutting lathe was made by James Watt - He used a common lather called a big Wheel that was driven by several heavy workers taking turns at the large fly wheel that powered the lather - Gradually using then next generation more and more accurate lathes are made until you get to the standard you require

In general working to high tolerances requires you can first measure to that accuracy and that you have a standard with which to compare or all measurements will be different.

Whitworth developed the principle of standards when making guns for the UK army and needing common parts that could be interchanged even down to the level of screws and nut and bolts so he defined a standard for the whitworth thread that is still used today.

It begs the question: How do you make the measuring equipment in the first place: this was Maudsley's great innovation. Whitworth WORKED for Maudsley.

Steve

The way you make more accurate tools is to either account for the errors during design and manufacturing (ensure that the errors are in places which are noncritical), or to use more-accurate tooling/procedures.

In the case of RepRap, I believe the former applies. The critical measurement is the leadscrews, and those are NOT being manufactured by the previous generation of RepRap. Errors in the piece which mates to the screws can be absorbed either by always driving in a single direction with some effort to minimize backlash, or by shaping the threads which engage the screws so they're a sufficiently tight fit to apply pressure against both sides of the screw threads despite any manufacturing error. Either will ensure that manufacturing error in that component is not cumulative over successive generations.

Very interesting and useful concept. So you have in mind replicate tools with less accurate ones but tweak the measurements and make them accurate. Awesome!