The 6 dollar carbide scraper and you! (with micrographs)

[HeavyHanded]

Howdy, decided to take a quick and closer look at the common carbide scraper, have never used one before and was curious about the near universal disdain exhibited by many on the forum - folks act like they're warding off the 'evil eye'. Was hoping to come up with a best practices should someone be stuck with one or have to give advice regarding their use. Was also curious how difficult it might be to improve one to a tolerable level of use. Am not trying to get to the level of the ERU, which is garnering good reviews and boasts much R&D and tight manufacturing. Just what I could manage at my workbench.

I started out with just some basic use on a $5.99 carbide scraper - Chinese mfg, on a boning knife from my kitchen set that I never use. Right off the bat I noticed several things. These do load up with swarf and a cleaning with a toothbrush or similar helps keep them cutting well. Secondly, the one I tested had many small imperfections in the carbide scraper that result in serious problems. The first pics are fom the scraper as it was purchased. Was very difficult to get a "clean" edge as the defects kept cutting groves into/along the apex - couldn't get it to leave a well refined edge but would still be considered an improvement over dull. First two pics show the best I could manage. I held the unit stationary on its side and brought the knife to it with a light, overlapping scrubbing motion.

-------------------------------------------------------------------------------

I stropped it on paper on my Washboard and the depth of those edge issues jumped right out. You can see in the third pic where the "edge" actually pulled away from the backbevel because it was undercut and barely attached. The second pic shows what most of the edge looked like, it wasn't torn up along the entire length. At this stage it could slice newspaper, but was erratic as it went - vaguely similar to a knife honed with a circular grind on a very rough stone.

Probably the most important factors in using the low budget scraper are to keep it clean, use light pressure, and swap it end for end every couple passes to minimize imperfections in the cutter per side (this is the biggie).

-------------------------------------------------------------------------------


Next I pulled the cutters from the unit and ground them clean on a silicon carbide (Norton Econo) stone. I also ground a bit more pitch to them so I'd have a slightly more acute inclusive angle. They still had some scratch pattern but was along the cutting head, not with it. They looked like there shouldn't be any large dings to cause trouble. I also wound up unintentionally softening the outside cutting shoulders as I did my resurfacing freehand - couldn't keep it dead flat on the stone - I believe this negatively effected its ability to shear off the burr. Still a big improvement. Swapped it end for end every five or six passes and had to slightly microbevel it to remove the burr (mostly). Pics show it is now much cleaner and uniform - burr on the opposing side is worked back into the bevel similar to a steeling. Would cut newspaper pretty well, still not pushcutting but definitely better. Could just shave some arm hair. For most folks this would be a sharp edge, and if it could have cut the burr off a bit better would have been even more acceptable.

-------------------------------------------------------------------------------

Burnishing with plain paper on the Washboard only hepled this so much the first time, I suspect running a smooth steel along this sort of edge (parallel grind) would be far more effective but didn't have one handy. So I went straight to my white compound on paper. Took about 30-35 passes to clean it right up, stopping halfway to apply a fresh smear. Second pic shows what was left of the parallel scratches - not much. This was an interesting exercise in another way as it gave me a clean slate to see the effect of the multi-grit compound without any prior scratch pattern interference - 100% WB compound. First pic was after 15 passes, second was after the full 35. Arm hair now piling up on the blade and crosscutting newspaper with a push.

-------------------------------------------------------------------------------

Learned a bit from this, and gained an appreciation for how this humble tool might be a good alternative for some folks. Am not pretending to have gained any insight into Fred's ERU, but clearly if the stock units can be made better with ten minutes on a workbench, a load of R&D and proper tooling should make quite an improvement over the norm.

Martin

 

[rutcrazed]

Thank you for all you do H.H. This was a good read. Keep up the great work.

 

[Sadden]

Interesting read if nothing else.
Best results ive seen from a pull through.

 

[HeavyHanded]

Thank you for all you do H.H. This was a good read. Keep up the great work.

Glad you find it interesting! I'm a compulsive Noodler, and every time I experiment with stuff like this it only broadens my understanding overall.


Martin

 

[mtangent]

So, it sounds like these things work poorly due to poor execution & technique, rather than underlying concept.

 

[ryxlyx]

I think a lot of people miss the point on these. I used them extensively a couple decades ago in a skinning operation where we'd be using knives literally 15/18 hours a day. We'd buy cheap Chicago cutlery paring knives for 6/$25, and when they wore down, toss them and grab another. Very cost-effective way to keep knives at least useful, and it doesn't remove the steel that say, an electric sharpener would do.

I actually pulled one out of my box a couple weeks ago, and experimented w/ it on my 154CM beater that I'll cut anything up to graveled shingles w/. Was pleasantly surprised to be reminded that-- for this knife and this knife only-- it beats the heck outa running around dull. Guy's talk about all the damage you'll do to a blade. How much damage can you possibly do by scraping a 60-degree topcoat over a 40-degree secondary, that's honed over a 30-degree primary?

In a pinch, I would use it anywhere. Beats getting halfway thru a pile of muskrats as it's getting dark, and the knife will no longer work....

 

[HeavyHanded]

So, it sounds like these things work poorly due to poor execution & technique, rather than underlying concept.

Its a bunch of things, starting with the instructions and the uninitiated sharpener's expectations, compounded by horrible QC.

Emboldened by my experience I decided if a few more minutes of thoughtful mods could make a bigger improvement.
Put the cutting heads against a right angle on the stone, flattened/re-established the outside corners and maybe squared them up. Also, it bothers me that the cutting heads contact each other, and what might be happening at that pinch point could really be causing issues with how clean an edge you can possibly get. I shimmed the heads apart by .012 with some shim stock, so there'd be a space for each head to contact 100% individually. Not sure if it is an issue, but I have a real problem with the heads contacting each other.

Lo and behold the edge did get a bit cleaner, less tear out and hanging dingles, and probably by virtue of holding onto more of the apex material, appears to be finer across the cutting edge. Could shave some arm hair and cut newspaper - not quite with a push but easily with a draw. Again, edge is very similar to one ground with a circular method in terms of how it cut (IMHO).

First pic at 100x, second at 400. The entire edge didn't look quite so pretty, but was in stretches and shows me proof of concept.

Am still not sure what to make of it, but certainly a useful tool under the right circumstances. I'd rather someone who hasn't been trained use one of these (or at least the one I mod'd) than a grooved steel on their kitchen knives. Substantially less damage and less chance of big issues at singe spots along the edge. It didn't take much clean up to make a big difference, and keep in mind the last pics here are straight off the scraper, no stropping on paper or anything else. Toughest part about using one is the final burr removal, but was very small. A few passes on a coffee cup or similar would really compliment this edge and take it up several notches I suspect.

 

[Bob6794]

If I am not mistaken a carbide scraper is typically one of those pull through sharpeners right? (And even if it's not I think there is still some relevant information I am going to use.)

Thank you for posting this up. My mom got one of those for Christmas from her parents as she doesn't know how to sharpen knives and she tends to dull them very fast by cutting on a glass cutting board. So I may have to quickly adopt a few things mentioned as advice and quickly learn how to use it to show her. As I know for a fact she won't use anything else, so mind as well make the best of what she will use.

 

[Mora2013]

Can you show pics of the $6 scraper and what you're doing to it?

 

[HeavyHanded]

Can you show pics of the $6 scraper and what you're doing to it?

Here's a pic of the entire set-up, and a closer one of the carbide cutter up against the brass plate I used for a guide. A piece of hardwood would have worked just as well, and a diamond plate would have been faster than my Econo stone. Can't really see what was done to the cutters, but was nothing fancier than running it lengthwise on the stone till it looked flat.

Econo stone, guide plate, one cutter, pieces of the scraper body, Washboard with paper and compound, two pieces of shim stock at .006 each and the other cutter.

I cut the head off the sharpener to make it easier to flip. Whole thing held together with two screws. For sharpening I kept the scraper on its side and brought the knife to it, held horizontal, flipping the scraper over every couple of passes. To deburr I used a sort of microbevel by angling the blade in the scraper and very lightly drawing it down. Pretty sure a ceramic or metal 'steel' to do a final deburr would work better than the scraper.

 

[Fred.Rowe]

Only a noodler would take this on; congrats, what would the human race come to with out noodlers.

Inserting shims to divide the abrasive strips, allowing the pile up at the "pinch point" to escape changes the results; I did this with my sharpener. Like you, I was experimenting, not really understanding what the outcome would be. But if you visualize what is taking place here, it makes seance to do so. It can't be positive for a hardened edge to be pulled through a trough made of a harder material with its own hardened swarf being pulled along with the edge. When I did a lot of wood finishing I found it important to "clear" the material, embedded in the sandpaper, regularly so as not to get high and low spots in the surface. If you let the paper load up, some areas of the surface would get sanded while other areas did not.

Good stuff, Fred