Edge Retention : 15 vs 20 dps - Sharpmaker Medium Rods

Methodology

Basic Procedure

edge bevel at 4-6 dps
micro-bevel at 15/20 dps, Spyderco Sharpmaker Medium Rods (12.5 micron)
slicing cut made through 2" of straight section of blade
sharpness is the edge length required to cut a cord under tension
cut speed is approximately 1 fps

In addition :

edges are checked under 50X mag before and after use
edge are reset (destressed) before sharpening
bevel before micro is set with a 700X bester (25+ micron)

Cardboard details :

1/8" ridged cardboard
random sampled
population has minimum 100:1 ratio over sample size
checked on a standard blade to ensure no long term drifting

In regards to the values :

5.0^-0.1(0.4)

means :

5.0 is the median performance
-0.1 is the change that the last run made to the median
0.4 is the standard deviation

As a rough check, as long as the runs are changing the median by more than the standard deviations it is unlikely the result is stable (i.e. the true value).

Results

Edge retention on 1/8" cardboard at 15, 10 and 5% of optimal sharpness
Knife	Angle	Initial Sharpness	15%	10%	5%
Knife	Angle	Initial Sharpness	cardboard cut (m)
Ai-De	15	50^-25(18)	1.1^+0.0(0.1)	3.1^-0.2(0.3)	14^{- 3}( 2)
Ai-De	20	68^{- 8}(30)	0.7^-0.1(0.1)	1.8^-0.4(0.1)	8^{- 3}( 1)
Galaxy Cleaver	15	56^{+ 2}(13)	1.3^-0.1(0.1)	3.5^-0.3(0.3)	15^{- 2}( 2)
Galaxy Cleaver	20	63^{- 8}(30)	0.9^-0.2(0.1)	2.3^-0.4(0.1)	9^{- 2}( 1)

In short, the Ai-De Chef knife shows a 77 (25)% increase in edge retention from the 20 to the 15 dps micro-bevel. A direct comparison :

and a point by point ratio comparison showing the consistent increase in performance by the 15 dps bevel :

The Galaxy showed a 69 (22) % increase :

and also showed the same consistent behavior :

Summary

As these knives are made from similar steels and the results are consistent they can be combined. With the data is pooled it shows an edge retention advantage of 66 (17) % increase when the angle is changed from 20 to 15 dps.

Overview and Discussion

In regards to the lower angle having increased edge retention the reasons are :

the 15 dps edge is already strong enough to resist rolling
there is no issue with carbide tear out or fracture in such low carbide steels
the higher angle concentrates forces around the edge
as the edge angle increases it takes less metal removed to increase the width of the apex

Thus increasing the edge angle does not offer a practical increase in strength and durability as it already is strong and durable enough to resist damage at 15 dps. The increased edge angle just makes the edge into a heavier wedge which actually thickens faster under a given amount of wear and the wear will be accelerated due to concentration of forces around the edge due to the higher angle.

Contact + Commentary

Comments can be emailed to

Most of the pictures in the above are in the edge retention album at PhotoBucket.

Last updated :	16/09/2013
Originally written:	26/11/2013