A forum friend of mine was kind enough to send me these Boride CS-HD stones to try out.
They are a Silicon Carbide (SiC) based stone. Edge pro users are familiar with the 120 grit CS-HD as it is the stone sold by Edge Pro for edge creation and reprofiling. However, this is one stone in a series of stones that Boride Engineered Abrasives markets as polishing stones. They are designed by Boride to be used on harder modern steels (HRC 60+).
At first blush, marketing a SiC stone as a polishing stone might seem a bit odd. Especially since, due to the way SiC cuts steel, it does not produce much luster if any. Knife people tend to think of “polish” as luster. In other words, The more polish there is the more like a mirror the edge becomes. However, smoothness of finish is what I think Boride is trying for here.
Here is a photo of the test setup with the test knife.
The edge angle on this knife was about 40 degrees inclusive before the test. There were two small chips in the edge as well. The chips were no deeper than half of the edge bevel. I began testing the CS-HD stones by reprofiling the blade edge to 30 degrees inclusive.
Prior to testing, all the stones were flattened. The 120 and 220 CS-HD stones were flattened on a DMT8XXC. The remaining stones were flattened with a Shapton Diamond Lapping Plate.
Reprofiling the edge of the blade and removing the chips tooks about 20 minutes, which was about 15 minutes way too long. Although Edge Pro markets the 120 CD-HD stone for stock removal, the stone does not perform well for this function. The binder in the stone is too hard for roughing. The stone slid over the surface of the edge while removing minimal amounts of steel. Not surprisingly, this really is a polishing stone designed to remove the scratch pattern from a previous stone. The 120 CS-HD is no substitute for a good roughing stone.
After the new edge bevel was created and repair completed, the edge appears even and the scratch pattern on the edge bevel looks uniform. Push cutting newspaper was difficult but achievable 3 inches from the hand.
The 220 CS-HD stone was similar to the 120 CS-HD stone. It’s very hard, does not remove steel quickly, and the scratch pattern on the blade is fairly uniform. Push cutting newspaper was much easier up to 3 inches from the hand.
The first thing you notice about the CS-HD stones labeled as 400 grit and higher is that they are lighter in color than the 120 and 220 stones. So far there have been no surprises since most every Edge Pro user has experienced the 120 grit stone. The 400+ stones are formulated differently. As soon as I started to sharpen with the 400 CS-HD stone, my expectations were shattered. The stone didn’t merely slide over the edge bevel. It gripped the steel and abraded it perfectly. I was ready to move to the next stone after just a few swipes. The swarf on the stone was almost all steel. Unnoticeable amounts of stone was removed while sharpening. This stone reminded me how much a stone’s “feel” is important, even when using a guided system.
The scratch pattern is very uniform. There are no noticeable scratches from the previous stone and the scratch pattern is uniform. Push cutting newspaper was extremely easy. The paper would slice fairly cleanly at about 4 1/2″ from the hand.
The 600 CS-HD stone had the same feel and sharpened just as fast as the 400.
The scratch pattern was still very uniform. There were no noticeable scratches from the previous stone. Push cutting newspaper was extremely easy. The paper would slice cleanly at about 5″ to 6″ from the hand.
The 1000 grit stone fell in line with the previous two stones. Excellent feel and finish. As was expected, the edge appearance was still matte, even at that high of a grit.
While the edge appears much cleaner, the knife’s cutting performance did not improve. Push cutting newspaper was no easier than with the 600 grit edge. As far as utility is concerned, the 600 edge may have been slightly better. This concludes testing the CS-HD stones.
To see if the edge could be further refined with stock Edge Pro finishing stones, I soaked and flattened the Boride AS-9 1000 grit and 1200 grit stones. These are Aluminum Oxide (AO) based stones. Here is the resulting scratch pattern from the AS-9 1000 following the CS-HD 1000.
This is also where the photo doesn’t tell the whole story about what is actually going on. While fine scratches are clearly visible here, they are not visible to the naked eye. I primarily used a circular sharpening motion and I really worked the edge with the stone. I finished with light edge leading strokes. The polish the AS-9 1000 stone gave this edge is the best I’ve seen from this stone yet. It was truly a near mirror finish with very little cloudiness. This AO finish also greatly increased cutting performance. Pieces of newspaper were flying everywhere.
The same held true for the AS-9 1200 stone…
…better near perfect mirror. Push cutting couldn’t get any better.
I finished polishing the blade with a leather strop (no tapes) which erased all but very few of the microscopic scratches. Unfortunately, the light on my USB scope is always on. The reflection of the light from the scope kept me from getting a useful picture.
Concluding Summary and Opinions:
The Boride CS-HD stones are good hard polishing stones. For knives, there are many better stone choices for roughing, reprofiling, and edge repair. The mid range (400 and 600 grit stones) is where the stones really shine. To bad Edge Pro doesn’t sell these instead of their regular mid-range stones. The CS-HD stones cut quicker, more evenly, and prepare the edge for finishing better than their AS-9 counterparts. The price of the stones from Boride reflect this too, as they are more expensive