The Super Scraper
My students, colleagues and I are always thinking or hearing about tools we’d like to see. Some of them are real tools that do some job better than the ones we're used to; some are better or cheaper editions of old favorites and some are purely wishful thinking and will never exist in the real world. This page is a showcase for all of them, real or imaginary. It is left as an exercise for the viewer to distinguish between them, although I will try to identify the imaginary tools with the ACME label:
I am not, nor do I intend to become, a supplier of lutherie tools. If I know a source for a tool, I will try to include the information and links.
In Il Segreti di Stradivari Simone Sacconni wrote (p 46) : ... scrapers were made from blades of sabers. Since they were of very hard steel one could not turn the edge and therefore they were used like a knife. When I began working with Carleen Hutchins she used such a scraper, and I have finally made some for myself. This is, in my estimation, the best possible scraper for builders of arched instruments.
It works on the same principle as scraping with a broken piece of glass; a common technique among carpenters. A very hard material can take an exceedingly keen edge and when it is perpendicular, as it is in broken glass, it can last for a long time even if the material is brittle. This tool has the advantage over glass of having a shape that is well defined and re-sharpenable.
The scraper shown above was made from a power hacksaw blade. My students and I have made several out of O-1 oil hardening tool steel. The thickness should be 3/32" or a little more. I find it easiest to rough shape the tool with a file before hardening it. It is heated (O-1 steel requires about 1450° F) and quenched to bring it to full hardness. This will normally cause some warpage. I have hollow ground the surfaces of mine to facilitate leveling the edge. Do not anneal or temper it to remove the warp as it will reduce the keenness and edge holding ability. Once the surface can be polished level all the way around the scraper it can be sharpened.
I find it easiest to hollow grind the edge perpendicular to the centerline of the scraper:
Simply set the tool rest on your grinder perpendicular to the wheel and grind all around. Use as fine a wheel as possible and don't apply too much pressure. If desired, the edge can be further dressed on a fine stone with or without a guide block.
In use, this scraper will give an extremely smooth cut even on soft or highly figured wood. It has little tendency to chatter due to it's weight and does not heat up. It is much easier on the thumbs than a normal scraper as it is not sprung in use. To re-sharpen simply lap the surface on a fine stone and re-grind the edge.
The scraper shown was sharpened after the ASIA Symposium in March and retained a usable edge for two months. It took less then two minutes to re-sharpen. My kind of tool!
At present there is no source I know of for this type of scraper, but one of the major lutherie tool suppliers has expressed an interest in making them. If they do, I'm sure they will let you know through their ubiquitous catalog.