How to do it, and how to become pretty good at it
In preparing this material, my goal has been to make it useful to both the beginner and the experienced worker.
If you have little or no experience with scraping, the first part should enable you to develop step by step the skills you are looking for, in a way that each step will build on the previous ones, and will lead you seamlessly to the more advanced topics.
If you already have experience with scraping and are looking for ways to increase your skills, I believe this may be the kind of material you have been looking for.
If you are an experienced craftsman, perhaps with years of scraping behind you, you will find here a number of approaches, some unconventional, some well known but at times considered from a different angle, and some that perhaps you will find to be new, which I hope will blend with the skills you already have. Also, you may find what is here useful for guiding others with less experience, toward greater proficiency.
My first exposure to metal scraping was in Italy in the 1950's, as a teenager. I made friends with a skilled Master Scraper, and was fortunate that he let me hang around his shop, so I got to observe him and his Apprentices at work, on and off, several hours a week for a number of years. Although that probably delayed my puberty by a year or more, it gave me a direct sense for what high quality metalworking, and scraping in particular, are like, which I have treasured ever since. It also gave me the opportunity to observe how a Master Scraper goes about teaching others who have various degrees of proficiency. Eventually I went through his complete training program.
Metal scraping is a technique for removing, progressively and in a controlled way, very thin layers of metal from the high areas of a surface, making it increasingly even until it reaches a very high degree of flatness. Think of a metal surface as having high and low areas, like miniature hills and valleys of a terrain. With each scraping pass you remove some material from the peaks, and so make them lower. After a sufficient number of passes, you will have brought the peaks down to the level of the valleys, and the surface will have become flat.
Learning to scrape is easy. It is easier than learning to ride a bicycle, swim, run a lathe, use a hand plane, carve wood, or for that matter use a metal file properly. In my opinion, the aura of difficulty and even mystery that has surrounded metal scraping has been due to the difficulty in finding clear and practical information about how to do it. Of course, like with any other skill, mastering the finer points of scraping metal takes patience, care, perseverance, and determination. And like with any other skill, or art, no matter how much one has learned there is always more one can learn. Yet with only a moderate investment of time and energy, you can learn to scrape metal surfaces with a routine accuracy comparable to a good grinding job. And as scraping becomes a natural part of your repertoire of skills, the occasions in which you will find it useful, even essential, will steadily increase.
Scraping can be done inexpensively. If you need to watch your finances, and have already a bench grinder with a cool grinding wheel, you can buy or make the essentials you will need to do a wide range of scraping, within a budget of around $100 (in 2012). With again that much you can get also several "nice to have" and some bells and whistles. And with a few hundred dollars more you can get setup to grind, lap, and even make, your own carbide scrapers.
Once you will have learned to scrape with some proficiency, you will be able to recondition many worn out or even damaged measuring and layout tools, your own or those you can find inexpensively at flea markets, on ebay, or from retiring machinists, and restore and even surpass their original performance. That includes, with the use of carbide scrapers, tools that are hardened and ground. You will also be able to make your own precision tools, as well as attachments, jigs, and accessories to extend the capabilities of your equipment, which could not be made satisfactorily without scraping some of the critical surfaces. And, perhaps most importantly, once you can take for granted that you will be able to scrape certain surfaces as needed, you will be able to conceive new projects with a greater degree of freedom, and enhance their design accordingly,
Scraping is also essential to bring lathes, milling machines, and machine tools in general to their best performance. Not only worn out machines in need of reconditioning, but perhaps even more these days, many of the new small low cost machines aimed at the amateur market, that are becoming increasingly available. More and more of their sliding surfaces are merely milled, and not always to the best a milling machine can do. As we know, if the sliding surfaces are not finished properly their movement will be uneven, accuracy and resettability will suffer, there will be lack of rigidity in operation, and more rapid wear of the surfaces. That wear in turn will require more frequent adjustment of the gibs, and increasing difficulty to do so properly along their full range. In time, as someone said, "you can tighten it, or move it, but not both at the same time."
Scraping can improve the situation substantially, sometimes even dramatically. With careful scraping and some TLC in other areas, even a very inexpensively built or worn out machine usually can be turned into a precision and high performance tool. A well scraped machine will have the smoothness and "velvet feel" that makes it a pleasure to use, and will give many years of accurate and trouble free service. And when it eventually wears out, you can scrape it again, and again make it work like new.
The material you will find here begins assuming that you have no previous experience in scraping, takes you step by step through the fundamentals, and is designed to give you an early hands on experience. It then covers intermediate subjects, such as changing the way to mark a surface as it progresses toward its final flatness, common pitfalls encountered during scraping and how to get around them, scraping dovetails and other sliding surfaces, or testing a surface for instability and detecting convexity. It then deals with a number of advanced topics, such as techniques to produce high grade surfaces, scraping hardened steel, pinpointing, or marking by evaporation.
At the end you will find a number of projects for building or upgrading tools and small machines, where scraping is central. They will show and illustrate in detail how to apply what we will have described, and what scraping can be used for. Some of those tools can find their place in any well equipped workshop, and you might want to replicate them directly. Others, more specialized, may suggest different projects along the same lines.
I would have liked to make this available free, but, let's face it, I have to eat. So as a compromise, HERE is a free preview of the complete package, intended to be nourishing by itself as well as to wet your appetite for the whole thing.
Or if you have already decided that you want the complete package, click HERE to order.