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Having trouble sharpening a curved drawknife

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Forum topic by ColonelTravis posted 11-21-2014 02:09 AM 1823 views 0 times favorited 22 replies Add to Favorites Watch
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ColonelTravis

1190 posts in 1357 days


11-21-2014 02:09 AM

Topic tags/keywords: drawknife sharpen

Just got around to try to use this thing I picked up a while back and the blade gently curves. Sorry for the stupid question, but is that on purpose or is it bent from use? It’s difficult to sharpen well. I’ve used a file and it’s better than when I got it, but it’s not up to my standards and it gets hung up in the wood too many times instead of scraping like it should. Tried an oilstone by hand and that was making the parts I filed dull again. Obviously not doing that technique right. Any suggestions for a curved surface? Grinder? I have no idea what kind of jig to use/make to get a steady angle.


22 replies so far

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TravisH

452 posts in 1398 days


#1 posted 11-21-2014 03:11 AM

When I bought mine from the “antique” store I first focused on lapping the back. I used a combination of stones and sandpaper and worked on pulling it sweeping it towards a handle, repeat sweeping to the other handle. After that I focused on the bevel. I held one handle and pressed the other side into my stomach and used a smooth cut file to work the bevel. I then went to a wet stone and rubbed the bevel until polished and smooth.

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TheWoodenOyster

1275 posts in 1398 days


#2 posted 11-21-2014 03:15 AM

This is the method I use. I don’t know if it’ll work on a curved surface. I guess it would depend on which side the bevel is on. Is the bevel on the concave side or the convex side?

-- The Wood Is Your Oyster

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ColonelTravis

1190 posts in 1357 days


#3 posted 11-21-2014 03:57 AM

Bevel is on the concave side. I’ve seen that video, Oyster, thanks. Saw some others but didn’t see anything with a blade curved like mine. Maybe I should look into how to sharpen a scorp.

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summerfi

3315 posts in 1150 days


#4 posted 11-21-2014 04:26 AM

Admittedly I’ve not personally seen a ton of draw knives, but I’ve never seen one curved in that plane. In the plane 90 degrees to that, yes, but in that plane no. I’m wondering if it may be bent. Also, you mentioned that it doesn’t “scrape” like it should. Maybe you selected the wrong word, but a draw knife shouldn’t scrape. It should cut smoothly just like a knife or a plane iron. Is there a maker’s stamp on the tool? A picture 90 degrees from those (laying flat) may shed some light on things too.

-- Bob, Missoula, MT -- Rocky Mountain Saw Works http://www.rmsaws.com/p/about-us.html

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unbob

718 posts in 1366 days


#5 posted 11-21-2014 05:33 AM

My secret weapon is a 10” Witherby draw knife with the same blade curve. Lucky the craftsman from long ago did not take it to a bench grinder, but instead used a stone.

Because of the curve, I use narrow long stones. I don’t think there is a way to properly sharpen the knife with any type of guide or machine. When using the knife, I stop and touch the edge when needed using a Hard Arkansas stone. Just very slightly tilting the stone until the micro burrs can be felt and dressed off both sides of the blade. The result is a deadly sharp edge that can remove wood at times faster then a machine. With the blade bevel up, wood contact is reduced and makes the hardest wood easier to work down. Bevel down, cuts finer, with some time using the knife very fine cuts can be made. My Witherby is double curved, also has a wide radius on the edge…adjustable handles.

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JohnChung

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#6 posted 11-21-2014 07:19 AM

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runswithscissors

2187 posts in 1488 days


#7 posted 11-21-2014 08:18 AM

When I was a kid the draw knife was one of the few wood shaping tools at my disposal. I never could use it “right side up.” That is, with the bevel up. It just wanted to dig in, not slice. With the bevel down, toward the wood, it could be very aggressive, and hog off big chunks, or quite capable of delicate slices of wood. A very versatile tool, though I was using it instead of a bandsaw (for example) to shape curves in wood. At least it was better than teeth.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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ColonelTravis

1190 posts in 1357 days


#8 posted 11-21-2014 01:22 PM

unbob, mine’s also a Witherby. (Bought it because all my chisels are Witherby.) Handles are not adjustable. I can sharpen planes and chisels great. Curved? Never done that. A narrow stone is the only thing I could think of myself, but the most narrow I have is 2”. You have something more narrow?

Bob, yes, I do mean “cut” and not “scrape.” Sometimes I’d get some nice slices on a portion of the knife and think – this thing is great. Most the time was not like that. Bevel was up, bevel down didn’t get me anything, which also tells me it’s not sharp enough.

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upchuck

540 posts in 1128 days


#9 posted 11-21-2014 01:45 PM

ColonelTravis-

I have a half of a dozen or so drawknives. They are a variety of sizes and also vary from straight to bent/curved both front to back and top to bottom. The curve on your knife does not seem out of the ordinary to me.

Draw knives are a pain in the butt to sharpen the first time during a tool restoration. There is a whole lot of blade there to shape, sharpen, hone and polish. But they are well worth the effort because they are such a useful and versatile tool. The Brian Boggs video that JohnChung recommended above is good for the last part of the procedure. Curtis Buchanan has a couple of detailed videos that show how to safely grind a drawknife and a different method of sharpening, honing and polishing. I use Buchanan for tool restoration and Boggs for touch up while using.

While I know that there are jigs available to hone draw knives it’s seemed like a waste of money to me. Buchanan uses a clamp on his tool rest when he grinds his knives. That has worked well for me also. I think that a key to drawknife grinding is a light touch and a moving rhythm as you slide the blade against the stone.

Good Luck.

chuck

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TheWoodenOyster

1275 posts in 1398 days


#10 posted 11-21-2014 02:17 PM

I see what you are saying about the wider the stone, the less likely it is to sharpen. I rough sharpened mine with a 1” file, then 325 DMT, then 1200 DMT, then strop. They make little 1” diamond stones for things like this, but I still don’t know if that’d work. You could just glue a piece of sandpaper onto a skinny and slightly curved face, like a half round file shape but made of wood. That’d probably work. Then make a skinny little strop with the same profile. I found my drawknife steel to be relatively soft compared to other tool steel. Hopefully yours is too and will take an edge quickly.

-- The Wood Is Your Oyster

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bold1

262 posts in 1310 days


#11 posted 11-21-2014 02:51 PM

If you check for stones, look for ones listed for scythes. As they are designed for sharping the curved blades.

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mahdee

3551 posts in 1230 days


#12 posted 11-21-2014 04:13 PM

I would try the largest chainsaw file and while holding it at an angle, maybe 25 degree, make your strokes left to right while simultaneously going up.

-- earthartandfoods.com

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Dallas

3599 posts in 1950 days


#13 posted 11-21-2014 04:47 PM

It’s just my opinion, but it looks like someone tried to use it somewhat like a froe and split a chunk of wood off that was too thick.
I had one somewhat like that that my brother and I ruined when we were kids. I think my dad wore out the strop on us, without polishing compound!

-- Improvise.... Adapt...... Overcome!

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mahdee

3551 posts in 1230 days


#14 posted 11-21-2014 06:15 PM

LOL, Dallas. You may be right about this. I have several of these and off course a fro in case my kids want to make shingles. Most curved draw knives I’ve seen have a much deeper curve than this one.

-- earthartandfoods.com

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jdh122

879 posts in 2280 days


#15 posted 11-21-2014 07:09 PM

I have no doubt that curved drawknives have an advantage in some situations. For coopers they’re essential, but with a heavier curve than that. Around here used drawknives at flea markets sell for so little money (less than $20), and they’re so much easier to sharpen, that I’d probably just buy a straight one if I were you. Unless you have a specific reason for wanting the curve.

As for sharpening the one you have, you can do the outside curve with any flat stone. I’d stay away from a file, as I doubt that the steel in most drawknives is soft enough to get much good out of a file. For the inside curve you can probably grind it on a bench grinder after crowning the wheel a bit with your wheel dresser. Then you can hone it with carving slips or using a round sanding attachment in your drill press. Finish with a wooden dowel with honing compound (if you don’t have drill press sanding capabilities, the second step would be that same dowel wrapped in sandpaper).

As others have said, it shouldn’t cut like a scraper at all. Not entirely like a plane either, somewhere between splitting and shaving, what Mike Abbot describes as sheaving (shearing/shaving). It’s one of the coolest feelings in woodworking, especially with green oak. You can also pull off thinner shavings.

All drawknives can be used bevel-up or -down, but the orientation of the handles determines which is comfortable.

-- Jeremy, in the Acadian forests

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