Cliff Stamp
BANNED
- Joined
- Oct 5, 1998
- Messages
- 17,562
I started the edge testing on rope this weekend. I used 3/8" hemp simply because I could buy it in bundles of 50 feet. I used a slicing cut done over 2" of blade. I picked 2" as the cut length simply because that was the size of some of the smaller blades I wanted to evaluate. The cutting was performed on a scale and after each round of cuts I would would do two tests of sharpness to gauge the extent of blunting. I would measure the amount of force (in g) it took for the blade to cut a piece of thread and the length of edge (in cm) it took to slice through 1/4" poly under a 1000 g load.
The knife was sharpened fully before the cutting. The entire edge would be cut back with a 1000 g waterstone, producing a full burr four times to ensure fresh metal at the edge. Then I would use a 600 and then 1200 grit diamond plate to re-cut the edge, ensuring optimal carbide composition. The 1200 grit stone would be alternated side to side on each pass to reduce the burr. I would them polish the edge lightly on a fine ceramic, using 15 strokes per side, alternating to ensure no burr.
After all the cutting was done, the blade would then be steeled and the sharpness again tested as a check for loss of material vs deformation as the cause of blunting. Then the whole process would be repeated two more times including the full sharpening. All the data was then collected into one large group. The repetition allowed me to verify my sharpening was not skewing the results as well as to refine the precision and accuracy of the results, by reducing the variance due to the composition of the poly as well as the way I was cutting it.
Here are the results for a Carbon V Twistmaster from Cold Steel :
http://www.physics.mun.ca/~sstamp/images/carbon_v_thread.gif
http://www.physics.mun.ca/~sstamp/images/carbon_v_poly.gif
http://www.physics.mun.ca/~sstamp/images/carbon_v_hemp.gif
I kept doubling the # of cuts for each round as I knew from past experience that blunting is strongly nonlinear. The blade starts off very sharp, 125 +/- 13 g on the thread, 0.575 +/- 0.054 cm on the poly, and 25 +/- 2 lbs on the hemp. This is about the best I have seen on edges in the ~20 degree range. This blade will shave effortlessly, push cut photocopy paper etc. . It will also stand up very well to hard chopping (in a blade designed for it), thus is is not by any means weak.
On to the work :
Note how little the force to cut the 3/8" hemp is effected, especially in the later rounds. I stopped after 62 cuts (rounds of 2,4,8,16,32 cuts), because the blade at that time could no longer cut the 1/4" poly, it would just skid along the cord. Even after the round of 16 cuts, (30 cuts in total), the blade could no longer shave, was down to about 11% of its ability on the poly, and about 35% on the thread. It was very blunt and in general could not do precise cuts well. However, it could still readily cut the 3/8" hemp, and even after another 32 cuts (60 in total) I did not see a significant change in cutting ability in that area.
After steeling (15 passes per side, Razor Edge Steel set at 33 degrees), the blade only goes back to about 61 +/- 5 % of its initial ability. On knives with a very strong wear resistance, steeling will restor them very close to 100%. The performance will only be off optimal by about 5-10% or so, which you would expect given the edge tends to have a small burr after steeling. Thus since the Carbon V blade doesn't get close to 100% after steeling you can infer that a significant amount of wear took place, about 30-40% of the blunting can thus be correlated to wear.
I think the above is a decent gauge for low stress edge retention as it involves both deformation and wear. The one thing I think could be added is another run right after steeling. This would show the advantage of the blades with a strong wear resistance. Obviously other blades are needed to put the above in perspective. Next I am going to run a low class blade (AISI 420 class), as a low end benchmark and them move on to high performance materials. I might also explore the difference in edge finish and see if edge angle makes a difference to edge retention on the 3/8" hemp. It would also be interesting to repeat this on another Twistmaster to check the QC.
More info on the Twistmaster :
http://www.bladeforums.com/forums/showthread.php?s=&threadid=175216
-Cliff
The knife was sharpened fully before the cutting. The entire edge would be cut back with a 1000 g waterstone, producing a full burr four times to ensure fresh metal at the edge. Then I would use a 600 and then 1200 grit diamond plate to re-cut the edge, ensuring optimal carbide composition. The 1200 grit stone would be alternated side to side on each pass to reduce the burr. I would them polish the edge lightly on a fine ceramic, using 15 strokes per side, alternating to ensure no burr.
After all the cutting was done, the blade would then be steeled and the sharpness again tested as a check for loss of material vs deformation as the cause of blunting. Then the whole process would be repeated two more times including the full sharpening. All the data was then collected into one large group. The repetition allowed me to verify my sharpening was not skewing the results as well as to refine the precision and accuracy of the results, by reducing the variance due to the composition of the poly as well as the way I was cutting it.
Here are the results for a Carbon V Twistmaster from Cold Steel :
http://www.physics.mun.ca/~sstamp/images/carbon_v_thread.gif
http://www.physics.mun.ca/~sstamp/images/carbon_v_poly.gif
http://www.physics.mun.ca/~sstamp/images/carbon_v_hemp.gif
I kept doubling the # of cuts for each round as I knew from past experience that blunting is strongly nonlinear. The blade starts off very sharp, 125 +/- 13 g on the thread, 0.575 +/- 0.054 cm on the poly, and 25 +/- 2 lbs on the hemp. This is about the best I have seen on edges in the ~20 degree range. This blade will shave effortlessly, push cut photocopy paper etc. . It will also stand up very well to hard chopping (in a blade designed for it), thus is is not by any means weak.
On to the work :
Note how little the force to cut the 3/8" hemp is effected, especially in the later rounds. I stopped after 62 cuts (rounds of 2,4,8,16,32 cuts), because the blade at that time could no longer cut the 1/4" poly, it would just skid along the cord. Even after the round of 16 cuts, (30 cuts in total), the blade could no longer shave, was down to about 11% of its ability on the poly, and about 35% on the thread. It was very blunt and in general could not do precise cuts well. However, it could still readily cut the 3/8" hemp, and even after another 32 cuts (60 in total) I did not see a significant change in cutting ability in that area.
After steeling (15 passes per side, Razor Edge Steel set at 33 degrees), the blade only goes back to about 61 +/- 5 % of its initial ability. On knives with a very strong wear resistance, steeling will restor them very close to 100%. The performance will only be off optimal by about 5-10% or so, which you would expect given the edge tends to have a small burr after steeling. Thus since the Carbon V blade doesn't get close to 100% after steeling you can infer that a significant amount of wear took place, about 30-40% of the blunting can thus be correlated to wear.
I think the above is a decent gauge for low stress edge retention as it involves both deformation and wear. The one thing I think could be added is another run right after steeling. This would show the advantage of the blades with a strong wear resistance. Obviously other blades are needed to put the above in perspective. Next I am going to run a low class blade (AISI 420 class), as a low end benchmark and them move on to high performance materials. I might also explore the difference in edge finish and see if edge angle makes a difference to edge retention on the 3/8" hemp. It would also be interesting to repeat this on another Twistmaster to check the QC.
More info on the Twistmaster :
http://www.bladeforums.com/forums/showthread.php?s=&threadid=175216
-Cliff