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jfmckenna:
We did make a video on sharpening those: it should be on the Stew-Mac site. Basically, it's easiest if you have a bench grinder. I use the 'fine' wheel: I don't know offhand what the grit is. Set the tool rest so that the wheel hits the edge of the scraper in the center of the thickness: that way you're grinding perpendicular the the face and get the same sort of burr on both edges. Lap the surface flat to get rid of the burr: I use a diamond stone but a belt sander works too. Run the scraper edge around the grinder to produce a new burr.

I like to touch the edge up on a stone between grindings, again, using the diamond stone. After lapping the surface I just hold it up perpendicular to the stone (the hollow grind makes this easy) and rub across the edge until you get a new burr. This really helps maintain the straightness of the flat edge between grindings. The fine, sharp burr really works well on figured woods, and also on softwood. I don't use any sandpaper on fiddles, but just go with the scraped surface from this fine burr.

One of the big advantages of the hard scraper IMO is that it's so much easier to sharpen once you know how. If you don't have a bench grinder you could try a carbide skate sharpener. It has a much tighter radius than the grinder, but once you've established the hollow it should work well.

Thanks Alan. I do have a bench grinder. I will look for that video.

We had a lengthy discussion in the shop on this subject, which - as is often the case with individuals intent on getting the last word on a topic - continued via text and secure message app over the course of the work week. In summary:

A standard 6" x 2-1/4" card scraper (5-7/8" x 2-1/2" for some European sourced scrapers such as the Bahco/Sandvik) is perfect for the job on a flattop. Scrapers only work well when they are very sharp, and as scraping binding usually involves cutting through lots and lots of glue, frequent resharpening will be necessary if the job is to proceed with any sort of dispatch. For much of the work, it is only necessary to put a rough edge on the scraper - one directly from a mill file, and a quick consolidation and turn of the rough burr...this process takes perhaps 60 seconds from start to finish, so 5-6 sharpening cycles consumes far less time than trying to continue the job with a dull tool. We usually don't bother stoning the edges until all of the excess adhesive has been removed, and it's time for a final light pass with a fine edge (although some makers will go directly to P220 at this stage, bypassing a final scrape).

One of the key advantages to the commonly available medium-weight (0.030"-0.035" thickness) card scraper is length - long enough to bridge the entire width of the side and bindings, which simplifies maintenance of a flat, true side, and dramatically speeds up the process of bringing things flush versus having to work each binding individually.

While working both bindings at the same time - a task impossible for scrapers much under about 5" - speeds up working the sides, that additional edge length also makes it easier and faster to bring the top and back bindings down with very little angular deviation from what is already introduced by the top and back radius. With one side of the edge safe'd, there is still considerable blade length left to ensure the scraper is skewed from the grain direction by 15 degrees or more.

Worth noting re: card and other un-jigged, straight-edged scrapers:

- Safe the same end of both edges when working the top and back...when dull (dust versus shaving, and hopping over versus cutting through glue), tape the other end and strip off the tape on the still sharp portion of the edges

- Skew the blade by at least 15 degrees from the top or back grain direction on softwoods and some hardwoods with varying surface hardness to avoid having the scraper 'hoop' from early-wood to early- wood (and creating a corrugated, torn-out surface)

- The scraper will tend to follow lumps and bumps of glue; frequent changes in skew angle - even a few degrees when working the sides - will allow these lumps and bumps to be efficiently leveled

- The area where wooden binding joins over the neck and tail blocks, at the corners of a Florentine cutaway, and the corner of the body/cutaway join on a Venetian cutaway can be a challenge due to the limited registration or inability to get much of a skew angle change...use a sharp, clean 8" or 10" mill bastard file with a tape-safe'd end to work these small areas once the bulk of the leveling is done elsewhere

- A 10" or 12" mill bastard and a scraper/saw jointer (we like the simpler Veritas 90 degree-only model without the 45 degree surface added in the later variant of the tool, but both are acceptable) makes quick work of stripping off the spent burrs on a card scraper (be careful - the ends of the scraper are very sharp). Consolidation and generation of a burr on the edge is useful but may not be needed for coarse work.

I should mention that we do have and use the Carruth scrapers in this shop for a number of jobs, and find them most suitable for working instruments with carved or pressed arched tops and backs. With an 8" CBN wheel and Veritas tool stands, sharpening can be done without heat build-up and with reasonable speed. But with all respect due Mr. Carruth and his brilliant scrapers, I would suggest that the humble card scraper is a tool better suited to the rough-and-tumble job of cutting through all that abrasive adhesive to get the initial level of bindings done in a reasonable amount of time.

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Good insights Woody.

I have often thought about a tool that would be a mix of your process and the hard scraper. That would be a long, hard* scraper that could span the depth of a typical ribset allowing you to more easily scrape both bindings at the same time or flush up the side to the bindings all at once. I find it difficult to do that with a card scraper because I always end up adding some flex to the scraper. I suppose I am blaming the tool for my lack of skill but I still feel like a hard scraper would be easier and probably stay sharper longer for this task.

* I recognize that was unfortunate phrasing

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You could make a hard scraper from a 6" or 8" joiner knife.

Full disclosure:
I learned about hard scrapers from Carleen Hutchins, who got the idea from Saconni, who said that was what Strad used. The hard scraper I use is the first one I ground from a power hacksaw blade. As it happens, it's M2 steel alloy. When my students tried it they insisted on getting them, and we ended up making them in the classes, usually from A2 or D2 alloy. One of the students has a brother-in-law who runs a machine shop, and I helped them work up the design of the scrapers they're now selling through the usual suppliers. For a number of reasons revolving around cost they ended up using D2. My scraper holds an edge about three times as long as the commercial ones. I would love to see somebody come out with the 'delux' version in M2, but it would probably cost twice as much. I don't get any sort of remuneration on those scrapers, and was surprised when they put my name on them, although I do understand why they did.

I’ve been traveling for work this week but I’m glad the question brought out all this good data.

I’ve been leaving the binding 0.020 proud which I think I can eliminate now that I’m using CA.

Good idea about knocking the inside edge off, I will try that.

Brad


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