Quick question on ideal edge geometry

fast14riot

fast14riot

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Oct 27, 2010
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I'm ready to put an edge on a little fixed blade whittler and was wondering what an ideal geometry would be. Its made from 1084, HT with my 2BF, quench in warmed canola, temper 1.5 hours 2x at 375*F. I did a full flat grind and its now down to .007" at the edge.

Should I use my standard 30* inclusive edge at .007 for a whittler? Should I bring it down to .005" and go steeper on the angle? I want a keen edge and for it to last. I don't really whittle much because I don't like using slip joints and I don't have any fixed blades small enough to be ideal for it, so I don't really know what is prefered.


-Xander
 
You have contrasting requests. You want the edge keen, but want it to last. A whittler/carver will strop and sharpen his knife very often.
I use about 20-25° inclusive for a fine carving tool, and start with a fairly thin edge.
 
Thanx Stacy, I guess you are right. I may have used improper terminology referring to a keen edge. I want a thin edge bevel, but an angle not too thin to cause rolling with the 1084. I know my HT is about as close as I can get it with a 2BF compared to a kiln, so if there is a certain limit that 1084 can go to for reasonable use between sharpenings that's what I am looking for.

Thank you for the recommendations, as well. I spoke with a friend of mine who is a knife maker but got into it from makin his own wood carving tools, he said that most are about 20* and Rc 60-63 (in 1095 steel). I assume this should be ok for 1084, but I'm expecting my knife to Rc at about 58-59 considering the HT and temper.


-Xander
 
That should be a good general use knife. Whittlers and cutting tools are often made from hyper-eutectiod steel and have harder edges. 1095 , W2, or the Hitachi steels are common in these type of tools. However, a 1084 knife at Rc58-59 will still be a good cutter if the edge is right.

After finishing the knife blade ( but before the handle is put on), sharpening it, setting the edge at 20°. It helps to warp the tang in tape or paracord to get some sort of grip. Then test it by carving up a 1" stick ( broom handle or maple dowel). Examine the edge with a magnifier several times during this test. If it rolls or chips, try resharpening it at 25°, and if necessary again at 30°. Hopefully, one of those will cut well with the least edge problems. If it still has problems at 30°, the HT may be off. Always rolling means the edge is too soft. Always chipping means the edge is too hard. You can re-temper a too hard blade, but there isn't much to do for a too soft one.
 
Just for informational purposes if it was too soft, and it didn't have a handle on it could it be heat treated again?

What would the proper proceedure be for re-hardening?

Thanks

Jeff
 
Iwannashoot - Yes, it could be HT again. Mine is a stick tang so I have a little room to grind the edge back to .020" to reheat treat, as .007" is too thin. A full tang knife may not be so easy due to design contraints.

I'm confident in my HT, I dropped the blade after I tempered it and was grinding. The edge was ~.010" and (of course) it landed tip down on the concrete floor. The floor chipped and just the very smallest amount of the knife tip chipped as well, so I just ground the spine down a little bit.

Thanx again Stacy, that is a good idea. I don't expect to do any serious carving or chip carving with this knife, just general whittling of bass wood and balsa. Maybe some pine or cedar at the most, but I don't have maple readily available here.


-Xander
 
The problem with a second HT on a thin knife with an already sharpened edge is that warp, edge ripple, and decarb may make the second HT not worth the loss in blade size. You would have to grind the edge back to get into the good steel. Most of the time, unless it is a very complex blade shape, it is faster just to grind a new blade.

TIP:
In the thinness of these type blades, it is often easier to grind the bevels after HT.
 
Yes, most of the whittlers are closer to 1/16" thick stock. I did mine from 1/8" but did ~ 3/4" tall profile giving a little less than 5* primary bevels to try and accommodate for the thicker stock. It is a nice thin grind. It should work well enough for me.


-Xander
 
I take my flats down to zero(burr) prior to adding my final bevel. I do this for carvers and choppers, alike. You would be surprized how thin you can go.
 
Thanx for that little tid-bit of info Rick. I'm thinking I'm gonna try that, I like that idea, less steel to remove when setting the bevels.


-X
 
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