In the beginning of the Structural Edge Tester (SET) development, Mike Brubacher experimented with perpendicular load on the edge.

FLAT IMPACTOR (flat end of a steel rod)
2140 grams = about 4.7 lbs load on a hardened 5/16" steel rod did not effect the burr-free edge of a mid-range Henkel chef's knife - the same BESS reading of 160 BESS and unchanged optical microscopy.

RADIUS IMPACTOR (round of a steel rod)
"If you recall, in our earlier test with the 5/16" rod end this amount of weight didn't affect the edge. With only the radius of the 1" diameter rod contacting the edge now, it did and substantially so, seen both on the sharpness tester (from 150 BESS to 700) and under x140 magnification.”

FURTHER TESTS with the rod
1000 grams load rolled the edge of 150 BESS by 325 points (measured 475 BESS). "Once again we can see the rolled edge at 140X."

Mike's flat impactor tells us that a flat load of 2+ kg (4.7 lbs) is absolutely safe for a burr-free edge.
We therefore based our Wire Edge Detector on a copper roller.

Experimental results follow.

COPPER ROLLER

Steel: ELMAX HRC 62
Edge angle 13 dps
Copper roller Ø 3/4”
Impact assembly weight 153 gram
1-cycle roll (FW-BW) perpendicular to the edge
Sharpness tester BESS PT50A

Clean apex

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	99	104	5
2	93	103	10
3	98	108	10
Average	96.6	105
AVERAGE WORSENING			8.3 BESS

Wire Edge

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	105	145	40
2	99	146	47
3	91	132	41
Average	98.3	141
AVERAGE WORSENING			42.6 BESS

***

Steel: S110V HRC 63
Edge angle 13 dps
Copper roller Ø 3/4”
Impact assembly weight 153 gram
1-cycle roll (FW-BW) perpendicular to the edge
Sharpness tester BESS PT50A

Clean apex

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	90	67
2	77	65
3	94	100
Average	87	77.3
AVERAGE WORSENING			*Improved by 10*

Wire Edge

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	91	95
2	85	100
3	77	94
Average	84.3	96.3
AVERAGE WORSENING			12 BESS

***

Steel: D2
Edge angle 13 dps
Copper roller Ø 3/4”
Impact assembly weight 153 gram
1-cycle roll (FW-BW) perpendicular to the edge
Sharpness tester BESS PT50A

Clean apex

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	82	99
2	115	105
3	114	108
Average	103.6	104
AVERAGE WORSENING			none

Steel: D2
Edge angle 13 dps
Copper roller Ø 3/4”
Impact assembly weight 153 gram
2-cycles roll (FW-BW & FW-BW) perpendicular to the edge
Sharpness tester BESS PT50A

Clean apex

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	71	76
2	72	71
3	85	62
Average	76	69.6
AVERAGE WORSENING			*Improved by 7*

***

Steel: SWIBO HRC 58
Edge angle 13 dps
Copper roller Ø 3/4”
Impact assembly weight 153 gram
1-cycle roll (FW-BW) perpendicular to the edge
Sharpness tester BESS PT50A

Clean apex

Knife No	BEFORE	AFTER ROLLING	Difference BESS
1	163	167	6
2	154	130	-24
3	184	175	-9
Average	85	115
AVERAGE WORSENING			*Improved by 27*

Wire Edge

Knife No	BEFORE	AFTER ROLLING	Difference BESS
1	99	116
2	107	126
3	91	206
Average	99	149
AVERAGE WORSENING			50 BESS

Conclusion: The cut-off value for clean robust edge apex is <= 10 BESS using a copper roller of diameter 3/4” and impact assembly weight 150 grams.

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STEEL ROLLER

Steel: ELMAX HRC 62
Edge angle 13 dps
Steel roller (linear bearing)
Impact assembly weight 150 gram
1-cycle roll (FW-BW) perpendicular to the edge
Sharpness tester BESS PT50A

Clean apex

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	95	214
2	97	202
3	111	236
Average	101	217
AVERAGE WORSENING			116 BESS

Wire Edge

Edge segment	BEFORE	AFTER ROLLING	Difference BESS
1	95	230
2	97	237
3	92	244
Average	95	237
AVERAGE WORSENING			142 BESS

Conclusion: steel roller is not suitable for wire edge detection.