When Fred offered to send me an ERU to test I had a good idea of what I wanted to do with it right away. There are certain materials that tend to dull my favorite knives out very quickly. I mostly use mild and simple steels like 1095, Sandvik 14C28N and recently have been using a really nice traditional pattern from Kershaw that is VG-1. I love these knives and theyre all generally in my everyday carry or everyday use category but I also tried it out on some kitchen knives that Ive never used and didnt know the angles for. Just trying to get an idea of how much work and effort would need to be put into restoring an unknown edge from an unknown angle.
But the ERU is the Edge Renewal Utility and the renewal portion of that is key here. When you take a very sharp edge into the field and you start using it on something really abrasive, it loses the edge pretty quick--of course Im talking in my own experience. You start wanting to get every last bit of cutting action out of it before having to go to your field hone because you know youll have to spend at least a few minutes just to get a serviceable edge--again your mileage may vary. In any case a lot of people have realized a long time ago that using a strop or a steel to touch that edge up before it gets too bad will keep them cutting for a long time and thats what I wanted to test this tool for.
Now the basic design of the tool is very simple, but simple ideas are usually the best ones. The ERU is essentially two circular discs with a small quadrant cut out from the center at a 90 degree angle. There are two carbide teeth opposing each other on each circle, and you can set the angle for a very wide variety of tools with this design and at exceptional accuracy and ease. The graduations marked go from 10 degrees ( inclusive ) up to 40 and are marked in 2 degree graduations but its very easy to set the edge degree by degree by simply setting half-way between. The lines are clear to read and deeply engraved so I dont see them wearing out any time soon. Past that it is possible to accommodate blades wider than 40 degrees and using a simple felt marker its easy to find the right angle for a blade even if you dont know the angle.
A key design feature that deserves its own mention is the carbide teeth themselves. A lot of times with these carbide sharpeners, the teeth act as cutting edges on the steel--theyre even angled at such offsets to deliberately attack the steel at an angle. This is not the case with the ERU, where the surfaces of the carbide inserts are flat and smooth, and at a perfect parallel to the bevel of a knife. This creates more of a smoothing and polishing effect than the cutting action associated with traditional pull through devices. I am not sure by what function these work mechanically but from a purely practical standpoint I think its comparable to steeling where its aligning and smoothing the edge on a harder surface.
The adjust-ability of the angle is also hugely important of course, but I think some other devices try to accomplish this and the smooth surfaces and fail. There are some pull-through type of sharpeners that use stone or ceramic wheels for instance, and they try to remain parallel to the bevel as well. However they dont have adjustable angles, and on top of that produce a lot of chatter and dont do an edge much better than the harsh carbide cutting bits of those types of devices.
You can get a good view of the carbide inserts and the tool itself with these pictures. The overhead view of the carbide inserts really shows how they are perfectly in-line with the centerline of that screw. There is a slight bit of risk of torquing the blade side to side, but one would have to be using the tool very, very sloppily for such a thing to happen. As a guy who takes a lot of pride and effort into sharpening, Im often very meticulous and so I thought Maybe Im not the one to judge this. So I let my friend David use the ERU on my Izula--one of my favorite knives so that ought to show you my confidence--and he is pretty much lacking in the meticulousness or pride in sharpening and more pragmatic. All I was interested in was having him making some cuts, sharpen it to where he felt an improvement, and then see if maybe the less-than-meticulous style of use would show some problems but this wasnt the case.
The whole thing is wrapped up in a pretty handsome package with a great sheath and compact shape. I mean one thing that stands out to me about this tool is that it can go right in your pocket, and come right out and be used whereas a lot of other guided sharpening tools are a lot more complicated to setup. I didnt think the sheath was really needed at first, but its actually pretty useful in giving you a bit of a handle for it. Depending on how large your knife is, youre going to want to hold your fingers a bit lower, and the sheath also acts as a stop by turning it around so the knurled screw sits atop the sheath. You wouldnt want it to suddenly slip into the sheath and it just makes it a bit sturdier feeling in hand. I didnt have a vise to test it out, but its also textured nicely to be able to grip padded vise jaws firmly and stay in place.
So onto how I tested and what I tested... First things first, I wanted to check out the angle-finding. The manual that comes along with the ERU instructs using a felt marker to find the high and low spots and find the angle by adjusting like this. Theres nothing wrong with this but what I was really curious about was how closely it matched the angles that I believed my knives edges were at, and thought it would be interesting to use it to find the angle of knives I havent re-profiled to a known degree yet. The tested knives were of a variety: I had a OXO brand pairing knife, a Kershaw Needs Work, an ESEE Izula and another Kershaw Wild Turkey traditional pattern. I used the ESEE Izula to do the final trial runs but used the ERU on all of these. The Wild Turkey, I wanted to find the angle--and it was a nice 32 degrees--and past that wanted to prove that people should have no hesitation to use nice or fancy knives in fear of scratching the blade. The Wild Turkey has a beautiful San Mai blade and a nice polish, and the ERU actually made the bevel look more polished and very nice and didnt leave a scratch on the rest of the blade surface.
You can see my first bit of testing was basically just checking the angles on knives, and seeing if they matched with the ERU. I use a caliper and trigonometry to find angles of knives and it was pretty quickly established that it was very accurate. I used the pairing knife because I never bothered to measure it using my traditional method measuring the spine from the hone. Anyway, I used the marker trick to determine that the edge on the pairing knife was 33 degrees. I measured the edge thickness at the shoulder and used the width of the bevels face and it worked out to 15 degrees per side. I wish I had a laser goniometer because measuring with the bevel thickness and face-width isnt very accurate, but its right in the ballpark so Im pretty sure its dead on. Moving past that to further substantiate it, I knew that my Kershaw Needs Work was set at 14 degrees per side ( using a stack of pennies for reference ) so I set the ERU to 28 degrees and it worked immediately. Now I tried to do the same with my Izula but I have a bit of a free-hand edge on it so it was a bit more obtuse than I had previously worked out and the bevels a bit convex, but using the ERU I found it was set to 40 degrees which was only 4 degrees over than my estimate. Okay so moving on past measuring the angles, Im satisfied theyre dead on and easy to find with a felt marker. Or if you have any experience using a machinists protractor to find the angle of a cutting bit I even managed to use it like that to find the angle without the marker.
What I was more concerned with though was how it actually effected the edge even despite seeing Freds pictures. The concern was that because the carbide teeth offset each other, that it would make a shearing motion and cause chatter on the edge of the blade. Basically tear it up and leave tiny little cuts where the carbide tore bits of steel out. That is how most of those carbide scrapers actually work, they dont do any polishing or anything and so they use a superficial edge that goes away immediately. This was not the case at all with the ERU and I used various scopes and magnifications to make sure of this. Unfortunately I dont have a USB scope or anything, but at 45x all the way up to 100x the bevel looked crisp and clean. The visible difference with the ERU is that lines formed were now parallel to the edge, and were very polished and smooth. They looked more like small striations on tool parts than grind markings. Very close to what a steeled edge looks like though Im not willing to suggest its the same mechanics, as typically with steeling one holds the edge at a slightly more obtuse angle. But the end result is extremely similar in my opinion.
But the ERU is the Edge Renewal Utility and the renewal portion of that is key here. When you take a very sharp edge into the field and you start using it on something really abrasive, it loses the edge pretty quick--of course Im talking in my own experience. You start wanting to get every last bit of cutting action out of it before having to go to your field hone because you know youll have to spend at least a few minutes just to get a serviceable edge--again your mileage may vary. In any case a lot of people have realized a long time ago that using a strop or a steel to touch that edge up before it gets too bad will keep them cutting for a long time and thats what I wanted to test this tool for.
Now the basic design of the tool is very simple, but simple ideas are usually the best ones. The ERU is essentially two circular discs with a small quadrant cut out from the center at a 90 degree angle. There are two carbide teeth opposing each other on each circle, and you can set the angle for a very wide variety of tools with this design and at exceptional accuracy and ease. The graduations marked go from 10 degrees ( inclusive ) up to 40 and are marked in 2 degree graduations but its very easy to set the edge degree by degree by simply setting half-way between. The lines are clear to read and deeply engraved so I dont see them wearing out any time soon. Past that it is possible to accommodate blades wider than 40 degrees and using a simple felt marker its easy to find the right angle for a blade even if you dont know the angle.
A key design feature that deserves its own mention is the carbide teeth themselves. A lot of times with these carbide sharpeners, the teeth act as cutting edges on the steel--theyre even angled at such offsets to deliberately attack the steel at an angle. This is not the case with the ERU, where the surfaces of the carbide inserts are flat and smooth, and at a perfect parallel to the bevel of a knife. This creates more of a smoothing and polishing effect than the cutting action associated with traditional pull through devices. I am not sure by what function these work mechanically but from a purely practical standpoint I think its comparable to steeling where its aligning and smoothing the edge on a harder surface.
The adjust-ability of the angle is also hugely important of course, but I think some other devices try to accomplish this and the smooth surfaces and fail. There are some pull-through type of sharpeners that use stone or ceramic wheels for instance, and they try to remain parallel to the bevel as well. However they dont have adjustable angles, and on top of that produce a lot of chatter and dont do an edge much better than the harsh carbide cutting bits of those types of devices.
You can get a good view of the carbide inserts and the tool itself with these pictures. The overhead view of the carbide inserts really shows how they are perfectly in-line with the centerline of that screw. There is a slight bit of risk of torquing the blade side to side, but one would have to be using the tool very, very sloppily for such a thing to happen. As a guy who takes a lot of pride and effort into sharpening, Im often very meticulous and so I thought Maybe Im not the one to judge this. So I let my friend David use the ERU on my Izula--one of my favorite knives so that ought to show you my confidence--and he is pretty much lacking in the meticulousness or pride in sharpening and more pragmatic. All I was interested in was having him making some cuts, sharpen it to where he felt an improvement, and then see if maybe the less-than-meticulous style of use would show some problems but this wasnt the case.
The whole thing is wrapped up in a pretty handsome package with a great sheath and compact shape. I mean one thing that stands out to me about this tool is that it can go right in your pocket, and come right out and be used whereas a lot of other guided sharpening tools are a lot more complicated to setup. I didnt think the sheath was really needed at first, but its actually pretty useful in giving you a bit of a handle for it. Depending on how large your knife is, youre going to want to hold your fingers a bit lower, and the sheath also acts as a stop by turning it around so the knurled screw sits atop the sheath. You wouldnt want it to suddenly slip into the sheath and it just makes it a bit sturdier feeling in hand. I didnt have a vise to test it out, but its also textured nicely to be able to grip padded vise jaws firmly and stay in place.
So onto how I tested and what I tested... First things first, I wanted to check out the angle-finding. The manual that comes along with the ERU instructs using a felt marker to find the high and low spots and find the angle by adjusting like this. Theres nothing wrong with this but what I was really curious about was how closely it matched the angles that I believed my knives edges were at, and thought it would be interesting to use it to find the angle of knives I havent re-profiled to a known degree yet. The tested knives were of a variety: I had a OXO brand pairing knife, a Kershaw Needs Work, an ESEE Izula and another Kershaw Wild Turkey traditional pattern. I used the ESEE Izula to do the final trial runs but used the ERU on all of these. The Wild Turkey, I wanted to find the angle--and it was a nice 32 degrees--and past that wanted to prove that people should have no hesitation to use nice or fancy knives in fear of scratching the blade. The Wild Turkey has a beautiful San Mai blade and a nice polish, and the ERU actually made the bevel look more polished and very nice and didnt leave a scratch on the rest of the blade surface.
You can see my first bit of testing was basically just checking the angles on knives, and seeing if they matched with the ERU. I use a caliper and trigonometry to find angles of knives and it was pretty quickly established that it was very accurate. I used the pairing knife because I never bothered to measure it using my traditional method measuring the spine from the hone. Anyway, I used the marker trick to determine that the edge on the pairing knife was 33 degrees. I measured the edge thickness at the shoulder and used the width of the bevels face and it worked out to 15 degrees per side. I wish I had a laser goniometer because measuring with the bevel thickness and face-width isnt very accurate, but its right in the ballpark so Im pretty sure its dead on. Moving past that to further substantiate it, I knew that my Kershaw Needs Work was set at 14 degrees per side ( using a stack of pennies for reference ) so I set the ERU to 28 degrees and it worked immediately. Now I tried to do the same with my Izula but I have a bit of a free-hand edge on it so it was a bit more obtuse than I had previously worked out and the bevels a bit convex, but using the ERU I found it was set to 40 degrees which was only 4 degrees over than my estimate. Okay so moving on past measuring the angles, Im satisfied theyre dead on and easy to find with a felt marker. Or if you have any experience using a machinists protractor to find the angle of a cutting bit I even managed to use it like that to find the angle without the marker.
What I was more concerned with though was how it actually effected the edge even despite seeing Freds pictures. The concern was that because the carbide teeth offset each other, that it would make a shearing motion and cause chatter on the edge of the blade. Basically tear it up and leave tiny little cuts where the carbide tore bits of steel out. That is how most of those carbide scrapers actually work, they dont do any polishing or anything and so they use a superficial edge that goes away immediately. This was not the case at all with the ERU and I used various scopes and magnifications to make sure of this. Unfortunately I dont have a USB scope or anything, but at 45x all the way up to 100x the bevel looked crisp and clean. The visible difference with the ERU is that lines formed were now parallel to the edge, and were very polished and smooth. They looked more like small striations on tool parts than grind markings. Very close to what a steeled edge looks like though Im not willing to suggest its the same mechanics, as typically with steeling one holds the edge at a slightly more obtuse angle. But the end result is extremely similar in my opinion.
haha j/k I'm glad to hear it works on steels other than the stuff I had available to test--I'm a fan of simple low-alloy steels, what can I say.
The ERU is now officially on my must-buy list. :thumbup: