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| Sharpening Chisels Question http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=12761 |
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| Author: | KenH [ Sun Jul 08, 2007 4:46 am ] |
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I had let my chisels get into awful shape and have spent a couple of nights sitting here honing them to perfection. One thing I happened to read (somewhere) is that chisels should have a double taper toward the tip and only the last bevel should be honed. In other words, the last 64th or 32nd of an inch of the tip of the chisel having the actual honing done on it at a different bevel angle than the rest of the cutting tip. I dont do this.... I grind so that there is one large bevel and then hone that one bevel to a mirror finish. They work well for me when they are sharpened like this, but I wonder if any of you do the double taper thing and if it is any beter than a single hone? |
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| Author: | Greg [ Sun Jul 08, 2007 5:13 am ] |
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I do what you do. I have heard also about the double taper but don't feel I am capable of doing one. So I keep it simple. KISS principle for me. |
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| Author: | JohnAbercrombie [ Sun Jul 08, 2007 5:20 am ] |
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I'm not sure it's any 'better' but using a secondary bevel sure makes touch-ups a lot faster. It also increases the bevel angle by a few degrees, but I don't find that I can notice the difference. Only the edge is doing the cutting, so it seems a bit of a waste of time to hone the whole surface- particularly if you are doing it by hand. I do hone the back of the blade to a mirror surface for an inch or so, as it makes doing square and miter cuts a lot easier. If I had a powered wetstone arrangement, I'd probably change my methods, but this is about all the hand honing I want to do! BTW, I keep a few 'utility' chisels for rough work and scraping duties- these get 'sharpened' on the 1x42 belt sander with the micron belts when I'm doing the kitchen knives. Cheers John |
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| Author: | KenH [ Sun Jul 08, 2007 6:11 am ] |
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I have one of the Veritas Mk II honing devices also Hesh and I have the same problem with skinny chisels. That really isnt so much of an issue as short chisels though. I'm not sure if my explanation was clear ont he forst post, but here is a picture of what I am talking about:
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| Author: | John How [ Sun Jul 08, 2007 6:31 am ] |
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I have the powered version of the MK II and do the double taper. It's a simple thing with that machine. After you make the primary bevel, you just switch to a thinner plater and without adjusting the blade in the holder, just run the edge again and it puts on the secondary bevel. |
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| Author: | davidmor [ Sun Jul 08, 2007 7:34 am ] |
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I do the double bevel simply because that is how I learned. It does make touch ups quick and easy though. I do hone and polish both tapers just because I like how it looks.  There ain't nothin' better feeling than shaving wood with a nice sharp chisel.  |
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| Author: | crazymanmichael [ Sun Jul 08, 2007 7:52 am ] |
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the purpose of the double bevel is to provide a relief angel. whether on a chisel or plane it reduces friction and promote the curl making the cut with less force. it also has the added benefit of making rehoning quicker as less metal has to be removed. if you are using a honing guide it takes no more skill to do a double bevel than a single. only the second, more inclined bevel on the edge needs be polished. this will get wider as you rehone over time. eventually, over time it will require the the primary bevel to be reground, and a new secondary cutting bevel honed on. with skinny chisels you can make spacers that are the thickness of the blade and put one on either side to keep it upright and square. |
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| Author: | psl53 [ Sun Jul 08, 2007 8:41 am ] |
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I always hone with a concave bevel on a wheel. It is similar to the double bevel, I then hone the leading edge to a finer point. Peter |
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| Author: | psl53 [ Sun Jul 08, 2007 10:08 am ] |
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Todd. Lucky you!!! Doesn't get any better than a Tormek, finished by setting an edge with a good hard Arkansas. Peter |
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| Author: | Billy T [ Mon Jul 09, 2007 3:27 am ] |
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There's also a reason for the double bevel, I believe, that is for cutting straight into work, like mortising. There is relief for the chip removal. Much like the back relief on the cutting lips of a drill bit. It isolates pressure more to a narrow cutting surface. Probably not much use to a luthier that mostly shaves braces. |
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| Author: | JohnAbercrombie [ Mon Jul 09, 2007 4:10 am ] |
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I'm a big fan of secondary bevels, but I don't see the arguments about 'reduced friction' and 'chip formation'- perhaps somebody can help get this concept through my addled brain? I think I'm confused about the distinction between the cutting angle-ie the angle of the 'wedge' shape at the cutting edge- and the various bevel systems. Admittedly, putting a secondary bevel on an edge increases the cutting angle, which may make the edge less fragile and reduce splitting. Let's consider a typical smoothing plane with bevel-down blade. Since the chip is formed on the 'flat' side of the blade, not the side with the bevel, any chip formation (and 'friction') has nothing to do with the bevel side. The same argument applies to chisels working 'bevel down', as Billy Thomas has indicated. I've never experienced much difference in 'friction' when using a chisel bevel-up and bevel-down on the same wood. I've always assumed that it's what happens in the first 0.1mm or so from the edge that mattered- that's where the cutting is happening. The rest of the tool only exists to support that small area of the edge. Cheers John (confused as usual) |
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| Author: | WaddyThomson [ Mon Jul 09, 2007 4:30 am ] |
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ISTM, that regardless of whether you choose to double bevel, or single bevel, the object is to get an edge down to as few microns as possible in thickness. As to optimum angle, that is something else again. I can see how it would be a major advantage if you have hollow ground edges, vs flat ground or convex ground edges which I have come to like.. However, when you touch up the edge on a strop board, or your 8000 grit stone, you sort of induce a bit of a compound bevel without thinking about it, albeit very microscopic. |
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| Author: | WaddyThomson [ Mon Jul 09, 2007 9:03 am ] |
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But, isn't the secondary bevel at a larger angle than the primary bevel? That would mean, as you said, pushing a 30* bevel through the wood instead of a 25* bevel, using standard angles. That seems like backwards logic other than the ease of touching up the blade. I'm not trying to be argumentative, I'm just trying to understand, and the logic is escaping me right now. Maybe if I go sharpen something, I'll get it better.  
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| Author: | crazymanmichael [ Mon Jul 09, 2007 11:13 am ] |
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read brian burns book. he explains it very well. |
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