Sharpening convex blades with sandpaper method

[texasrimfirenut]

So using the mousepad/sandpaper method for sharpening convex edges what grits do I use? I know it probably depends on how dull but what sandpapers do I need? 400, 600, 800, 1000 & 2000?

Also if I understand this correctly, I lay the knife flat when sharpening right and the cushion of the mouse pad will keep it right with just a little pressure instead of trying to hold the knife at a very low angle?

I've watched videos and did a lot of reading but am slow I guess and I wanted to confirm.

 

[Jason B.]

Use a strop as a backing, a mouse pad has too much give in the surface and puts way to much curve on things.


I usually like to start around 220 to get the profiling done quickly then progress to 400, 800, 1000 and strop. I reserve 2k for choppers where the extra polish helps.

Sharpening angle should only slightly change. Drop 2-3 degrees per side from the current edge angle and remember to use even pressure. If you sharpen flat then you will considerably thin the blade and edge to the point it will fail quickly. The idea with connvexing a non convex ground blade is to thin the bevel shoulders while making the apex angle slightly more obtuse.

 

[G. Scott H.]

Mouse pads can work, but you have to keep pressure very, very light. Thick leather (currently 8-9oz) works best for me, as it allows more pressure and makes for quicker work. For grits, I go from 120 through 1000. Once sharp, you can maintain on a strop, or you can use a rod system (SM, Lansky, etc.) to add a micro bevel, depending upon your preferences.

 

[texasrimfirenut]

Thanks guys, the blades are already sharp. Its the Fallkniven F1 & A1 knives that I have in convex.

I plan on really using them this weekend while camping and wanted to make sure I have whats needed to sharpen them back up.

I had bought 2000 grit sandpaper but seems like its kind of a mute point and I should go straight to the strop from 1000 grit.

I do have a leather strop with the "green" stuff on one side and just leather with nothing on it on the other side.

So far I haven't used the knives much and have just used the strop to bring them back to original edge.

What I've been doing on the strop is laying the blade flat and then angle it just a tad until the actual edge touches the leather.

Also since these already have a good edge, probably even after I use them a lot this weekend, should I start on up at 400 grit or above?

Sorry for all the questions but really do appreciate the help!

 

[texasrimfirenut]

Hmm so would it be appropriate to use my Spyderco Sharpmaker to touch up the edges with the fine and extra fine rods since the Lansky was mentioned? I was under the impression that would do away with the convex edge. Sorry again for being novice but I don't understand what a micro bevel is. I will google that.

 

[G. Scott H.]

A micro bevel is just a tiny, barely visible bevel added to an edge for increased edge strength and easier maintenance, since it's more obtuse than the rest of the edge. A micro bevel done on a rod system will be an angled bevel, but it's very, very tiny, and it doesn't seem to effect cutting ability in my experience. I've used micro bevels for a long time on a couple of Bark River blades, and they continue to act just like when they were new. I just find it easier to do a couple swipes on the rods every so often than to strop (personal preference), and in the event of a tiny chip or roll in the edge from use, the rods can actually repair these pretty effectively, without having to go back to sandpaper, whereas a strop won't by itself. And yes, you could use the SM to do the same thing.

 

[ziggy925]

I doubt anybody is going to get a perfect convex bevel on any knife, and why convex? Unless you are sharpening a hatchet, IMHO it seems to me a very slight micro bevel on a straight angle would be just as strong on a non-chopping knife. I'm just thinking in terms of easy sharpening.

 

[Jason B.]

I doubt anybody is going to get a perfect convex bevel on any knife, and why convex? Unless you are sharpening a hatchet, IMHO it seems to me a very slight micro bevel on a straight angle would be just as strong on a non-chopping knife. I'm just thinking in terms of easy sharpening.

Because his blades are convex and that's how you maintain them.

 

[HwangJino]

I think a good way to practice is to use a crayon on paper. The idea is the same, shaving small pieces of crayon/steel off with consistent strokes.

 

[Obsessed with Edges]

{ To texasrimfirenut }

Sandpaper sharpening happens to be my favorite method, by far. I'd like to offer a suggestion to try, maybe at your leisure, with a few 'practice' blades. The idea that convex sharpening is difficult is way overblown, as I see it. If you are comfortable with stropping technique, that's all you really need. All the other variables of introducing the convex shape to a blade, and doing the relatively heavy grinding in the early stages, can be accomplished in the selection of the materials you use.

Get yourself a piece of flat, smooth wood. A scrap of finish-grade plywood or MDF can be used, or any other wood that's smooth & relatively hard will do. Also get some wet/dry in grits from about 220/320/400 and up. Cut a piece of the wet/dry paper to fit your board, and use a 'glue stick' from the school supplies/arts & crafts section of your local Walmart or other big-box store to lightly tack the back of the paper for sticking (lightly) to the board. This will give it just enough tack to keep it from moving or lifting as you 'strop' your knife blade on the sandpaper. An ordinary stropping stroke on this firmly-backed sandpaper will introduce some visible convex, but not so much as to make your edge angle too thick/wide. On simpler steels, the 220/320-grits will work very fast, so it won't take many strokes to give you an idea of how it's working and shaping your edge. The firm backing under the paper, and the sticking of the paper to the board, also means the grit works much more aggressively, AND the lack of 'give' in the backing will also minimize/eliminate the tendency of the paper to roll around and over the blade, rounding the apex and also scratching the upper portions of the blade's primary grind.

Here's a 'glue stick' product I've been experimenting with for this; it works well enough for these uses, and makes removal/replacement of the paper easy:

Give this a try; it might surprise you. :thumbup:


David

 

[Ben Dover]

I prefer strops for maintaining a convex blade. I don't normally allow them to get dull enough to need sandpaper,

I did convex a large outdoor knife of 0170-6 converting from V to convex several years ago. This was mainly a curiosity to see if I could do it. I used 3M wet/dry, very wet, from 220 grit to 2500 grit on a rather thin, firm mouse pad and them strops to .5 micron.

If there was any improvement in cutting or edge holding, I was not able to detect it. IOW, simply not worth the considerable effort.

My Bark River and Fallkniven are maintained on float glass backed "Russian Red" strops with 6,3 and1 micron diamond.

On convex edges, I have not seen great improvement in going past 1 micron.

 

[texasrimfirenut]

Thanks guys, I will try as suggested.

Right now its kicking my butt but I refuse to give in just yet.

Went out and got a lot more grits of the paper today. Got everything from 220 up to 1000 and have some 2000 already.

I think part of my problem is I was jumping from some 220 I had to 2000 and not being successful.

Also it seems to be getting pretty sharp but not shaving sharp like they were when I got them in. Not for sure but I am also thinking I am applying too much pressure. It doesn't feel like I am but I read somewhere that error on the side of less pressure as a lot of times people use too much pressure.

I really do appreciate all the help. I will get there at some point and not going to give up, lol.

 

[Jason B.]

I sharpened two convex blades today, a blackjack 125 and blackjack woodsman. For the woodsman I hand sharpened on waterstones finishing at 6k, I'll have a video of that up in a few days. The 125 I did with sandpaper and finished with a polishing wheel.

For the 125 I started with a 1k waterstone to fix some of the geometry then followed with a sheet of 400 grit wet dry on a JRE sharpening block. With the sandpaper on a soft backing I still use a forward and back motion to keep the grind pattern parallel to the edge. With the scratch pattern blended and a burr raised with the 400 grit paper I then finished on a polishing wheel buffing the edge to razor sharpness.

Here are some pictures. Last picture is the woodsman.





(Two of the pic'a are upside down)

 

[HeavyHanded]

Thanks guys, I will try as suggested.

Right now its kicking my butt but I refuse to give in just yet.

Went out and got a lot more grits of the paper today. Got everything from 220 up to 1000 and have some 2000 already.

I think part of my problem is I was jumping from some 220 I had to 2000 and not being successful.

Also it seems to be getting pretty sharp but not shaving sharp like they were when I got them in. Not for sure but I am also thinking I am applying too much pressure. It doesn't feel like I am but I read somewhere that error on the side of less pressure as a lot of times people use too much pressure.

I really do appreciate all the help. I will get there at some point and not going to give up, lol.

It is very important when working with sandpaper to use very light pressure and clean the paper often - a pink eraser works great. Too much pressure on a dirty sheet, and the paper will load and clog - its effective life will plummet and the quality of the grinding will go downhill as well.

Martin

 

[SA Condor]

Wow! Very informative! I just ordered some sandpaper to use before my strop. Here's to hoping I can follow all your advice and get my knives right!

 

[Threethreethree]

I grew tired of the endless burr flip flopping induced by ceramic rods, their abysmally slow cutting speed and their tendancy to load in the blink of an eye and their total uselessness on very wide bevels...

SIC sandpaper was my cure and there is no way im going back to vitrified\hard stones, however i might pick a good JWS one day to try it out but im really satisfied with my cheapish set up consisting on a very firm thick leather ( tried the mousepad and hated the lack of control i had) epoxied to a piece of scrap wood, i use a C clamp on one end to keep it flat, i keep the other end with my left index finger ( im gonna try glue stick as i feel clumsy on very large knives going one handed though ).

I shape using 220 and lotsa oil, deburr on end grain beech then 600 with lotsa oil, near the end of the job i dope the sandpaper with white compound, deburr as much as i can then a little stropping and good to go.

No bullshit, no mystics, fast and effective.