How do I sharpen a blade that is fully convexed?

[vanacres]

I have a couple of convex blades that need to be sharpened, but I'm not sure how to go about it. I'm sure the information is already here, but I tried a few different searches and came up empty. I have been doing some sharpening freehand, and most days I'm pretty consistent, but sometimes not so much. I also have a cheap guided system (I think it's a Ruixin), that I have made some modifications to and have some good stones for. I get good results with the guided system.

Can I use a guided system for a blade that's convexed, or does it have to be freehand?

This is an Enzo Badger that I slightly dinged the edge on when I was putting scales on it:

 

[Danketch]

You can do pretty much what you want. Freehand is easiest for me to maintain full convex sharpening. Using a guided system can produce a convex edge (by sharpening at multiple angles and blending together, but wont sharpen a full convex grind).

Depending on steel, waterstones may be easier than a whetstone. I like using waterstones to fully sharpen mine at home, and will use DMT diamond sharpeners or a piece of sandpaper on a hard surface to sharpen in the field.

Search for convex sharpening and look at the stickies- there is a lot of information here.

You could look at a few videos on youtube as well - I think Izzy Turley has a few sharpening videos, this Japanese guy VirtuoVice is pretty good, and some of our members here as well.

 

[vanacres]

Thanks for the reply Danketch.

Yeah, I've watched a lot of videos and done a ton of reading here. Especially the stickies. Just don't recall seeing anything about a convexed blade where there really is no edge bevel. Seems like I would have to slightly rotate the knife on its axis as I draw it across the stone. Not sure I could be consistent with that.

 

[Danketch]

That's the whole point- you don't have to be consistent (at least not super precise)- just a slight rocking motion is all you need. Put some radial sharpie lines on the blade and start sharpening. You will see were you are abrading and where you are not. Modify your motion accordingly.

 

[Danketch]

To resharpen in the field, you can also use a tight circular scrubbing motion, this was the first way I could get any knife hair shaving sharp.

 

[Wowbagger]

I'm sure the information is already here, but I tried a few different searches and came up empty.

Ha, ha, don't feel bad half the time I can't even find posts that I have made and know all the key words. One "trick" is to go out on your web browser and Google your topic and then look for the ones listed for BladeForums.

As far as sharpening it I will leave that up to the brethren.
One thing you can do is go down the stone edge leading and feel the edge on the stone then lower the angle the tiniest amount (a degree or fraction of a degree) and take some forward and back strokes; this way you won't be constantly making the edge angle steeper / wider.

That's the best way I know to load up the pores in your nice fine grit stones and make them stop cutting so you can spend time conditioning and cleaning the pores. Not a fan.

I'm an Edge Pro Geek so what do I know.

 

[FortyTwoBlades]

The following presumes using a bench stone freehand, but you can change the phrasing for other methods:

If trying to maintain the current edge angle, lay the blade flat on the stone (or nearly flat) and slowly lift the spine until you see the edge make contact with the stone. That's your current edge angle. Now, sharpen away. Honestly, don't worry too much about maintaining the convex. Even using many guided systems can result in a slight convex depending on how the guides work, and you're not actually losing any tangible performance by doing it that way. It'd take many many sharpenings before you'd have to thin it out again, and that holds true of flat-ground blades, too. If you really want to bother with maintaining it and don't want to increase the edge angle by accident, find the angle, and then drop the spine by a consistent amount over the length of each stroke and work the blade in sections. You can even do a faceted approach where you sharpen at your intended edge angle and then sharpen at a couple of lower angles to bring the shoulder deeper and blend it in.

 

[palmerdl]

Since you already have a convex edge, you can use a leather strop with compound. The trick is light pressure... read almost no pressure... weight of the blade pressure. Tip the blade up until you see the edge touching as described by FortyTwoBlades above. If the edge is beyond just stropping, use wet/ dry sandpaper in progressively finer grits. Same pressure technique.

 

[FortyTwoBlades]

If stropping on any material softer than wood, I suggest using a slightly lower angle than the edge is at, because deflection of the strop material will widen the angle.

 

[Bigfattyt]

For a nick in the edge, you may have to go back to a stone. I've found even a simple diamond stone, with attention to angles (ie, not keeping the exact angle has been fine for my convex edges). As another has said, circular Mother's on can work fine, I pay attention on the shoulder to make sure I'm keeping the convex blended.




Now, when I first started with convex edges, the easiest way was edge trailing strokes on flat automotive sand paper. On top of a firm flat rubber backing, on top of a larger glass panel. Varring grits up to higher grit sandpaper. Taking it slow. Paying attention to keep pressure very light. Then, finishing on a loaded leather strop. Making sure the pressure, and the leather does not wrap the edge and actually dull it. I got hair whittling edges this way. Whittling free hainging hair with curls.


As time went on, I got a bit lazy, and stopped dragging out the kit for convex edges and started just using my old medium diamond stone and ceramic stick. Found I could get great maintenance on my edges that way too. Just had to practice a bit.





Here is an edge with a single grit of sandpaper (600 grit, straight to a strop with chromium oxide, if I remember correctly).

If you look closely, the hair is between the two knives above. Here is a close up of the curles shaved in the hair with it free hanging...