Fastest working edge convexing

Nosetotail

Nosetotail

Joined
Jun 10, 2007
Messages
398
Hey guys, I work in the high voltage electrical trade, and we use cheap straight edged square tipped chrome vanadium shoe makers knives. I have been putting a quick 30 degree v edge with a 40 degree micro bevel for some time. I use these angles for convenience use with a sharpmaker. The quality of the edge is not very important as a nominally shaving sharp edge is more than adequate to strip wire and cut insulation. Anything too sharp tends to actually slice into the copper underneath, and my apprentices often break pieces of wire they have cut too deep into. This kind of work ruins an edge very quickly and often to a significant degree.

I have actually known for sometime that the v edge is not the right edge for this type of work however I have stuck with it due to the relative ease that I can get a knife sharp, however I am growing tired of continually having to reset the v to get rid of the damage which I know is due in part to the v shape and my relatively low angles.

I am planning on experimenting with convexing by hand. We have in stock large rolls of 1.5" wide 80 grit aluminum oxide belt sand paper. I can achieve a convex edge in a matter of a couple of minutes with this stuff. I wish he had some finer grits for refining but we don't, and I really don't want to add a bunch of steps to this process. My plan is to use the rough side of a slack leather strop with a FAST cutting compound. So I'm wondering if something like the emery black cake from Sears would be the right choice for this or if you can recommend a better choice. Will an aggressive compound refine an edge enough, or will it leave me with issues? If I have to, I can sand the rough side of the leather to get something close to swede, but am wondering if the raw leather finish would be more effective.


I want this to be as effortless as possible, while still producing an effective working edge. I'm not very experienced with this, so any thoughts or suggestions are welcome.
 
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Unless you specifically need a refined edge, I would just find a wood block, cut into it to remove the burr, and go on with your day:thumbup:. Personally though, I would prefer using my WorkSharp mini-belt sander. The factory belts might eat up the blade if you're not careful, but you should need no more than a quick pass on each side with the P220 and 6000 grit belt to get the blades sharp for what you're doing. The belts don't really flex that much, so even if it is technically a convex edge, it probably doesn't have as much of a curve as what you're doing now. Though if razor sharpness is not a requirement, I'd suggest a 25 degree per side edge and send those apprentices on their merry way. Should only take about a minute or two per blade. Though the sharpener DOES need an outlet to work.
 
My favorite method for sharpening, involves a piece of 2-1/2" wide oak, 1/2" thick, and about 5-3/4" long, with leather on one side (about 1/16" thick). I simply cut a piece of wet/dry sandpaper to the same width (2-1/2"), but a bit longer, so I can wrap the paper over the ends of the block, to be held by my thumb & a couple of fingers of my left hand, while 'stropping' the knife on the sandpaper with my right hand. It's all very portable, and the sandpaper grit can be chosen according to preference. It can quickly put a convex edge on most any pocket-sized folder (starting from a v-bevel). I'd think something around 220-600 grit would put a basic working edge on a blade quickly and effectively, especially on an 'inexpensive' knife with relatively common, soft(ish) steel. It's all very portable, both the block and sandpaper could be put in a sandwich-sized zip-loc bag, and tossed into a toolbox or wherever you want to stash it.

I'd think the sandpaper would be preferable to trying to dress a strop with very coarse compound. Especially in the 'working edge' grit range (220-400, maybe 600), these can often be found in 'assortment' packs of wet/dry (3M) sandpaper, at Home Depot, Lowe's, Walmart, etc. The coarse grits do most of the 'grunt' work, and would be used up a little quicker, but the 400 and 600 would serve to maintain those edges for a good, long time, before wearing out.

Most of the V-bevel folders I've convexed so far, have been done starting with the 400 grit. If the V-bevel is decent to begin with, the 400 will quickly put a nice convex on it.
 
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Actually, I'm really concerned with the polishing compound/strop set up. The parameters I'm working under are using the truck stock I have available and don't have to pay for(80 grit belt sand paper), and then quickly refining the edge I get from 80 grit aluminum oxide. I work out of a bread van that has a work bench with a clamp. I have a box of the sand paper hanging over the work bench already, so I can just pull off a couple of feet, slap it in the clamp and wallah. It can't get anymore convenient than that.

I also already have the strop made and ready to hang. In fact it is already somewhat loaded with the emery black from a long time ago, but I plan on getting more depending on the feedback I get here. I'm just trying to figure out if this is going to present me with more issues with the edge, or if there is something I'm not aware of that I need to worry about, and if there is another more aggressive compound that would still give me a nice working edge, but not continually cost me money.

Incidentally, I have already learned that with this method that the angle at the edge is deceptively quite a bit more obtuse than it appears. I gave it a shot the other day thinking I had somewhat of a low angle, and then tried to touch it up at 40 degrees on the sharpmaker and didn't even touch the edge. I am actually considering convexing at a low angle with the sandpaper and then refining with the sharpmaker, but I'm not sure if this would defeat the purpose.
 
If you're sticking w/ 80 grit paper, then the black emery from Sears (approx 600 grit) is still a bit refined. I use a number of silicone carbide grits starting at 120 up to 1200 for stropping. 80 grit belt sander material is very aggressive stuff, I'd recommend beating it up some to wear it down a little, and then use some SiC lapping compound. My 120 and 220 grit compounds are from a lawnmower supply shop - the compound is used to sharpen gang reel mowers on a golf course. All the rest can be ordered very cheap, from any lapidary supply house or some hobby shops (sell items for gem and stone tumbling/polishing. For what you're trying to do, 120 or 220 grit would work very well and you might not even need to go back to the paper very often, as these compounds will restore most edges by themselves unless they're terrible worn.

HH
 
Perfect. What do you think about just turning the emery cloth on itself?

Anyway, that is exactly what I'm trying to figure out. I think I could sand the smooth side of my leather and load it with the 600 grit black cake and then find something like 220 or 400 for the rough side. I figured like you said that I wouldn't have to hit it with the paper as long as the edge doesn't get damaged, and the convex shape should go a long way towards keeping the edge away from the conductor.

The compounds you are talking about...are they in a hard cake like the sears buffing compound, or do they come softer. I'm just trying to think about eventually having to clean the strop.
 
The reel mower compounds are suspended in a water-based jell that quickly evaporates from leather leaving a loose grit, the lapidary compounds come as graded powders in small bags. I use a squirt of dish soap to make a slurry that dries pretty fast, leaving behind a slightly waxy base that the grit sticks to. Once they see some use the grit embeds into the leather a little and helps keep it in place as well. Should you need to rejuvenate the strop, a few drops of water and some agitation w/ a fingertip is all that's needed. If it gets really funky (which has not happened yet IME), you could just rinse the whole thing off under a tap while nylon brushing, let it dry, and start again. The lapidary powders are mighty cheap - about 5 bucks/pound which would last a lifetime. The Sears black emery is good match for 400-600 grit sandpaper should you care to upgrade from the 80 grit paper and not bother w/ "specialty" stropping compounds, though it doesn't restore a battered edge like the SiC powders. I cannot recommend this highly enough as a maintenance strategy for the lower grit ranges, and the edges produced are burr-free and very strong performers.

As for turning the emery cloth on itself, that might work, or you could rub it down with a flat chunk of metal or a brick.
 
Nosetotail said:
Actually, I'm really concerned with the polishing compound/strop set up. The parameters I'm working under are using the truck stock I have available and don't have to pay for(80 grit belt sand paper), and then quickly refining the edge I get from 80 grit aluminum oxide. I work out of a bread van that has a work bench with a clamp. I have a box of the sand paper hanging over the work bench already, so I can just pull off a couple of feet, slap it in the clamp and wallah. It can't get anymore convenient than that.

I also already have the strop made and ready to hang. In fact it is already somewhat loaded with the emery black from a long time ago, but I plan on getting more depending on the feedback I get here. I'm just trying to figure out if this is going to present me with more issues with the edge, or if there is something I'm not aware of that I need to worry about, and if there is another more aggressive compound that would still give me a nice working edge, but not continually cost me money.

Incidentally, I have already learned that with this method that the angle at the edge is deceptively quite a bit more obtuse than it appears. I gave it a shot the other day thinking I had somewhat of a low angle, and then tried to touch it up at 40 degrees on the sharpmaker and didn't even touch the edge. I am actually considering convexing at a low angle with the sandpaper and then refining with the sharpmaker, but I'm not sure if this would defeat the purpose.
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OK. If you've already got plans to use the strop w/coarse compound, nothing wrong with that. I hope it works well for you.

With regard to the 'deceptively obtuse' character of the convex edge, I went through this, too. I liked the edges I was getting, but noticed they weren't quite as 'shaving sharp' as I'd hoped. I attributed this to getting adjusted to the technique (translation: I wasn't quite good enough at it, yet. :p). I've gotten better with more 'practice', and by lowering the angle a bit more, like you mentioned. A firmer backing also helps with that, so I'm gravitating towards thinner leather and/or using a hard backing for finishing the very edge. I do this by flipping my block over, and using the sandpaper on the bare wood on the back. I've also noticed, by making a few, very light edge-leading passes on the paper this way, it seems to put some bite in the edge, especially if I do it at the very fine grit stage (1000/2000).

There's nothing wrong with using your sharpmaker to touch up your convex edge. I occasionally will make a few passes on a DMT hone to put some 'bite' back in mine. A lot of makers of convex blades actually produce them with a V-microbevel on the edge. The big advantage of convexing (as far as I'm concerned) is in the rounder/smoother shoulders of the bevel. Makes slicing through thicker material a whole lot slicker. When you get right down to it though, the very edge is still just an edge. It only matters if it's sharp or not. How you make it sharp is entirely up to you.
 
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Easiest way I convex is on a belt sander. I repair any edge damage and them work up a burr in the grit I want then buff the burr off with the slotted paper wheel.
 
This is one case where the advantages of convexing are very evident in practice. A v edge will lead to the edge driving into the copper or aluminum when stripping the insulation. Once it starts to cut into the conductor, then there is significant edge damage, and sometimes heavy chipping. These knives are about an inch wide brand new and barely 1/16" thick at the spine with a flat/scandi grind all the way to the edge, so chipping is an issue. As thin as they are, I don't think the convexing will add a significant amount of toughness, but if I can eliminate the edge being driven into the conductor, I can cut down on the damage quite a bit.

What I'm getting from your post is that I should try to hold my slack belts as tight as possible. I figured I would hold the spine just off of the belt to eliminate thinnig the knife any more than is necessary, and then try to judge my edge angle based on the angle of the belt coming off of the trailing edge. Of course I understand that there will be additional convexing going on due to the compression of the leather right at the edge, so I figure I will try to make things pretty acute to account for this. At the moment, all the knives I have already have a 30 degree v edge set on them, but I would like to start on a fresh knife with the original scandi grind just to see if I can maintain it 100 percent with the strop. This would be my special knife for fine slicing.
 
I've noted before that convexing is deceptively simple. I keep a variety of backing materials on hand depending on how much of the blade is going to be in contact w/ the sandpaper, and how thick the spine is. Generally I find I have to lower the spine from 5-8 degrees and as much as 10 degrees/side for a thick blade fully convexed, even w/ light pressure compared to a V grind. It is all too easy to make an overly obtuse edge. I do find I get the best results from a fairly conformable backing, very light pressure, and a very steep angle and make contact on or almost on the entire face of the blade. Convex edges at or just below 30 degrees inclusive are extremely efficient cutters.
HH
 
Well I tried the Sears black cake on the smoother side of my leather after I roughed it up a little with sand paper. The only way I could get it to take was to cake it on kind of thick. When I started stropping, the compound immediately started smoothing off giving me a shiny black surface on the high spots. I don't think this is metal build up given how quick it started smoothing off, but I don't really know as I don't really have much experience stropping with compounds. Any suggestions?
 
It's the wax binders that hold the block together. It also means you went a little heavy on the application. That said, the black compound will remove metal fairly quickly compared to green or white compound (CrO and AlumOx respectively), so if you could see the gray from the steel being left behind it would be pretty obvious.

A drop of liquid soap (I prefer dish soap) will break down the binders pretty thoroughly, allowing you to work your compound a lot thinner and more even. Try it again once its dried. You can also melt the waxes a little with a lighter, hot air gun etc and spread it out more that way. Some folks don't feel it matters much if it cakes up, but I believe it works a lot better when the texture of the leather combines w/ the abrasive, rather than just acting as a base for it.

HH
 
Well I'm not really digging how this black cake is acting on the leather. I'm wondering if I could get away with getting a big ole bottle of Walmart alcohol based hand cleaner jell to make the slurry with. I know I would have to rub it on quickly and it would dry completely and tend to dust off, but I figure If I get a pound of the SiC powder, it shouldn't be a problem to just keep refreshing the strop. It would only take a small handful of gell and a half a spoon full of powder each time. A drop of soap might even be a good addition like you suggested. What do you think?
 
Nosetotail said:
Well I'm not really digging how this black cake is acting on the leather. I'm wondering if I could get away with getting a big ole bottle of Walmart alcohol based hand cleaner jell to make the slurry with. I know I would have to rub it on quickly and it would dry completely and tend to dust off, but I figure If I get a pound of the SiC powder, it shouldn't be a problem to just keep refreshing the strop. It would only take a small handful of gell and a half a spoon full of powder each time. A drop of soap might even be a good addition like you suggested. What do you think?
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This is how I approach it, others may or may not agree. Generally speaking, I use the rough side of the leather when applying compound. I glue it or tack it to a piece of flat hardwood and sand the nap very low and tight. With the more coarse compounds I feel that using the rough side is mandatory.

With the black emery, you shouldn't really need a slurry, just put it on light and even and it'll do a good job of burr removal/modest refinement in the 400-800 grit range w/ best results at 600 grit. For a more even application I swear by a few drops of dish soap and work it very thin with a fingertip. You could use it coming off of 80 grit paper, but in that range you're probably better off just using a piece of scrap hardwood to remove the burr and accepting it for what it is, a hard use edge that will be abused and can be quickly restored. You cannot expect too much from the black emery or any other small grit compound coming off of 80 grit paper. 220 grit is probably the jump-off point for refining with commercial compounds, with the results improving as your grinding grit approaches the particle size of your compound. I believe the Sears emery is estimated at 600 grit.

When it comes to using the loose SIC powders I still swear by a blob of dish soap. Just look at the waxy goo that forms around the spout of your soap bottle as it dries- a little bit of this goes a long way. It soaks into the leather and becomes pretty much dry to the touch. It's more than enough to hold those powders in place, especially once you start to use them and the grit embeds in the leather somewhat. Some will fall off with use and handling and that's OK. If they stick too tight, they can't move around as the steel passes over them and instead of removing your burr, they create one. Mineral oil will also give very good results.

Coming off of 80 grit paper, I'd say you should go with 120 grit powder or even larger. Heck, some play sand or blasting grit might even be a good match for that grind pattern. I've never tried it and cannot recommend it, but it likely would work fine. You will not get good refinement at this level IME, but you will get a solid edge that can draw cut tough materials all day long. In my opinion it's not really worth doing finishing steps such as stropping on anything that's been sharpened at less than 120 grit. Just cut into a chunk of hardwood, strop it both sides at a fairly steep angle on the same hardwood a few times none too gently, and draw cut into it a second time. This will remove 80% of your burrs and any that survive this treatment should be welcome to join in the day's work. For a really tough edge, I don't go below 120 grit paper. Stropped on 120 SiC grit and the results would surprise many. It WILL shave a lot of arm hair, and it WILL push cut newspaper with the grain. You can't expect a whole lot more from an edge that took a couple of minutes to create and will all too soon get knocked about vigorously. Best of Luck

HH
 
Thanks HH, you have definitely been a lot of help. I'll probably take advantage of all the cardboard we have laying around and make me a big ole thick cardboard cutting block with a little bit of all the tape we have laying around. Can you suggest a good website you trust for some SiC powder?
 
I already have two knives convexed. Neither shave, but one did remove a few leg hairs. They strip wire just fine though. The real test will be on removing heavy jacket on some of our larger cable. This is where a really sharp knife comes in handy. I'm just using the 80 grit utility cloth and finishing with the Sears black cake. I brushed the excess compound away with a wire brush, so the strap is perfect for right now. I can go with this until I get some SiC powders ordered.
 
One other thing you can do to help get the finest edge off the 80 grit belt is to tack the ends tight over an opening. Picture a foot of 2x4 with a small block attached to each end that raises the belt off the surface of the board. Tack the belt taught across these blocks. Slack belt sharpening on the go. Otherwise the backing on those bonded sanding belts is so rigid it makes it tough to get a light, even contact even when placed over mousepad or leather. You have to pay close attention as the angle of deflection will change slightly when you travel from block to block, but not so much that it causes trouble. IME this is the best way to work by hand with the bonded belts if you want a real light touch - at 80 grit you want a light touch.

HH
 
You probably already have a cordless drill on the truck, so get a rubber or foam-backed sanding disc pad from HomeDepot. Get some PSA (Pressure Sensitive Adhesive) sandpaper, highest grit they have in stock and go to town. It will make a steeply convexed edge in a flash. Just hold the drill in one hand and the knife in the other. Start at the heel of the edge and work your way to the point. Practice will guide you toward the best feed, speed and angle for the disc. Make sure the rotation is from the spine of the blade toward the edge.

For the helluvit, I googled a few key words and manged to find these videos:

http://www.youtube.com/watch?v=wIZpF2OdkW8
http://www.youtube.com/watch?v=p6oW9ych8ho

Having reviewed the videos, I would like to point out that for her purposes a flat or hollow grind may be ideal, but for your application of cutting insulation away in a controlled manner I suggest you try a convex edge first. Both flat and convex can be achieved by using this sharpening method, it's only a matter of holding the blade steady using a stiffer disc, rolling it slightly on the disc, or using a softer more flexible disc to allow the abrasive to deflect therby casusing a concave grind. It's entirely up to the craftsman.

Good luck!
 
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