Note: In the next day or two, we will release our new card scraper over at Crucible Tool. In preparation for the release, I am preparing a lot of instructional material, including a video and a photo tutorial of how I sharpen a card scraper. You might find this helpful. You might not.
I’ve never met two people who sharpen their card scrapers using identical methods. As a result, there is more misinformation about sharpening card scrapers than sharpening any other woodworking tool. And that is saying a lot.
The following technique is based on 20 years of daily practice and a decade of research into historical methods. I won’t bore you with the spreadsheets and the bibliography. Instead, I’m going to explain the process using as few words as possible.
For those of you who learn using video information, I’ve also made a short film that will be released soon.
Step 1: Remove any Existing Burr or Hook
The first step for me is always – always – to burnish the faces of the scraper to eliminate any existing burr or hook. The burr could be the result of manufacturing. Or it is the remnants of the hook on the tool you’ve been using.
Place the scraper down flat near the edge of the workbench. Press the burnisher dead flat on the scraper. Press down – hard! – and glide the burnisher across the face of the tool. Five or six good strokes will do. Repeat on the other three faces.
Step 2: Stone the Narrow Edges
To get perfect 90° corners, use a block of wood as guide and stone the long edges of the tool. Shift the block of wood around so you don’t wear a groove in your stone. Use the sharpening stone that you use to begin your typical honing process (a #1,000-grit waterstone or a soft Arkansas oilstone, for example). Seven or 10 strokes should be enough to stone away any extra metal. (Note: There is no need to hone the short ends of the scraper as these don’t cut.)
If, however, this is a new scraper, you might need to stone the edges on a coarse stone for a few minutes to ensure the edges are dead 90° to the faces and consistent. Future stonings will go faster once the tool is set up.
Repeat this process with the block of wood on a polishing stone, such as a #5,000-grit waterstone or a hard Arkansas oilstone. Look closely and continue the work until the edge is consistently polished. The first time you do this on your tool it might take a few minutes. Subsequent sharpenings will require only 10 strokes or so.
Step 3: Burnish the Faces
Wipe a little oil on the scraper and the burnisher. Place the scraper flat on the bench again and repeat the same burnishing process you used to remove the burr. Remember: Use hard downward pressure (yet the burnisher should still glide across the face of the tool).
This burnishing polishes the face of the scraper (much the way a hard bone will burnish soft wood) and push a little steel up on the tool’s edge. This step improves the durability of your hook and makes the hook easier to turn.
Step 4: Burnish the Edges
Secure the scraper in a vise with one edge upright. Wipe a little oil on both the scraper and the burnisher to make your work easier. Hold the burnisher parallel to the floor and burnish the edge with moderate downward pressure (a bit less than you used on the faces). Five or six smooth strokes will do.
Tilt the burnisher about 5° to the right and burnish one corner of the scraper with five or six smooth strokes. Run your fingers up the scraper to feel if you have turned a hook. The hook is slight and subtle, much like the burr you turn on the backside of a chisel when sharpening it.
If the hook is not there, repeat with more strokes with the burnisher tilted at 5° to the right until a hook appears. Try adding more downward pressure to see if that helps.
When you have a hook, tilt the burnisher 5° to the left and repeat the burnishing process for the other corner. When you have two good hooks, flip the scraper over in the vise and repeat Step 4 for the second edge.
Clean the scraper with an oily rag and get to work. To improve the longevity of your burr, store the tool in a cardboard or paper envelope. The hook is as fragile as the edge on a paring chisel.
— Christopher Schwarz
So this is also how Calvin Cobb, Radio Woodworker, would do it?
Ha! I must have clicked that by accident. Nice catch, Mr. Detail Man.
Cool. I thought I had this down. These instructions already gave me two ideas I can use immediately. Block of wood on the sharpening stone to guarantee the 90 degrees, and the oil to make the burnishing easier. I used to make the local pets go nuts. Now I know why.
What is that burnishing tool you are using to turn the edge?
The Arno burnisher.
Do you ever use the other, sharp, side of the Arno burnished for anything?
It is useful for turning a hook on so-called “super-hard” scrapers. If I cannot get a hook turned on something, I flip the Arno over, and its pointed little friend finishes the job.
Lee Valley has a carbide sharpener that looks like the hindquarters of the Arno, though I’ve never used it. I experimented a little with the pointy Arno, but it never gave me better results than the round end. But all of my scrapers are pretty old, and not hard like some of their newer cousins.
Have you seen the process that Peter Galbert demonstrated in Fine Woodworking a few issues ago? It eliminates the chance of grooving your stones. Peter, as a chair maker, is also a person who uses curved scrapers daily.
I use the side of the stone for narrow things that might leave a grove.
I have found a fatal flaw to that after a few years. But if you haven’t – godspeed.
Chris, I know you will almost certainly stay mum because it might touch too closely on the sharpening wars, but I am too curious not to ask — would you mind sharing what about Pete’s approach you’ve found to be problematic?
I have to say that I’ve tried this method multiple times in my head, and have found the result less than optimal. Perhaps I’m doing it wrong?
That’s funny right there.
Maybe you are doing it correctly and you’re just not visualizing your shavings properly.
How might you adapt this process for concave scrapers, like ‘chair devils’?
Currently, I’m using a round file, then wet-dry sandpaper on an oak dowel before the burnishing rod. It seems to work, but I’m a neophyte so I have no basis of comparison – is there a best practice?
The reason there are so many ways to sharpen a scraper is that how it works depends on how you hold it, especially the angle. Everyone does that differently and needs a different burr. I hate using someone else’s scraper.
When you put it in a jig (your chair devil) and fix the angle of attack it’s a bit more important to make sure your burr is right. The best way to get that right is to slightly alter your angle through trial and error until you get something that works. You might find a concave hand held scraper useful for learning what the chair devil ought to be doing.
It’s simple to make a convex scraper by filing or grinding. For one like Chris is using, I would mark the shape out and clamp it in a vise a bit past the line, knock off the excess with a hammer (using eye protection), and then file the rest. Concave is a bit harder. If you have a full size commercial scraper (or old saw blade), you can snap it down to a size you like and then mark and grind. Scoring can help the snapping but isn’t strictly necessary if you are careful. Don’t burn the steel.
It’s easiest to somewhat match the radius of the file to the concave edge, but the last one I did was about a 4″ radius shaped with a small mill file (flat) and it worked just fine. Draw filing is best and that’s hard with a small diameter round file. Use a light touch and a fine single cut file if possible. To finish I use a round wood block maybe 3/4″ high of slightly smaller radius than the scraper with 150 grit sandpaper on its edge. I put the scraper and the block flat on a table and spin the block as I draw the abrasive down the edge. Having a few shims lets you raise or lower the scraper to use more of the paper. Repeat with finer paper if it makes you happy. I then stone the flat face
I sometimes add another step by burnishing the edge square first then drawing the burr out (Chris’s step 3) then move on to step 4. I do step 3 at a slight angle which I find works well with concave curved edges. The amount of pressure you use makes a huge difference. I lube with oil from my forehead or cheek.
If your chair devil has a thick blade you may want to file at an angle other than square, especially if the blade is close to perpendicular to the wood stock. You may not need a hooked edge and that may vary depending on the wood, your mood, and/or the cycle of the moon.
Great explanation! My teacher Phil Lowe always chides me about using a wood block, calls it “training wheels” but it does ensure a perfect 90.
Do you use a pointy tip on the scraper to turn back the burr, the way Phil teaches? I couldn’t get the hang of that, not for love or money.
John, I’m working on that. I use a 15x loupe to see if I’m getting the correct result. I’m getting it right about a third of the time. When I don’t get it right, I’m no worse off.
Minor correction: it’s not so much to turn back the burr but to put the burr at a repeatable/reliable angle. This has helped me consistently pick up shavings.
If there’s any way you could post a photo showing what the burr looks like under magnification when the scraper is ready for use, it would help me a lot–I’m having trouble understanding what I’m aiming for, which is making it tough for me to know whether I’m there.
(that’s a lie–I’m 100% sure I’m not there. I’m just not sure where “there” is)
I’m afraid I don’t have the magnification to show it. The hook is usually about .002″ in length. The only real test is to use it. If it makes shavings, you are there. Dust… not there. Probably the fastest way to learn it is to have someone teach you in person. They will immediately see your problem(s) and set you straight.