Becker CU/7 from Camillus : Combat Utility Knife


A shot of the Becker CU/7 alongside the TAC-11 from Tom Johanning :

cu7 and
	tac-11

The review consists of :

Description

The CU/7 is made by stock removal out of 0170-6C, a proprietary low alloy carbon steel used by Camillus. The knife weighs 370 with a neutral static balance. It is very wide for the stock thickness (3/16)" with a high primary flat grind of 4-5 degrees, with a small section of spine left at full thickness for strength. The edge was 0.036 +/- 0.002" thick behind the bevel, which was ground at 16 +/- 1 degrees. It has a black power coating and comes with a Cordura/Kydex sheath.

stock work

A few passes to test arm hair shaving showed basically scraping ability. Push cutting light thread the CU/7 took 185 (8) g, and 1.1 (1) cm slicing 1/4" poly under a 1000 g load. A quick check under magnification showed the edge was sharpened with a coarse abrasive and buffed, and is uneven with a slight burr.

Using a rocking cut, the CU/7 could section 3/8" hemp requiring between 40-44 lbs near the choil, and 34-36 lbs near the tip. With a fine polish there was little aggression, 33-35 lbs was required on a slice, two inch draw. With a 600 DMT finish, the blade was slightly more aggressive, needing 29 +/- 2 lbs to cut the same cord on a slice. Pointing some ends on a basswood dowel, the CU/7 needed 9.9 (4) cuts.

Compared to the Twistmaster from Cold Steel, the CU/7 is out cut almost two to one on the hemp, however both are near equal on the hardwood. This shows how belly and edge thinness are critical on rope, whereas the primary grind significantly comes into play on the hardwood whittling. There are also handle issues which influence the hardwood cutting. The grip on the CU/7 is ergonomic and allows a lot of force to be used which makes it efficient for heavy cutting. The rope cutting pretty much ignores handle issues and thus is simply a measure of the cutting ability of the blade (more specifically edge) in isolation.

Digging holes in 2x4's, the CU/7 took 35 (5) stabs and an average time of 2.7 (3) minutes.

field

The CU/7 both whittled and chopping scrap wood well. Even after heavy blade modifications to the SOG SEAL to thin out the edge and convex the primary grind, the CU/7 easily held its own. With both knives at the NIB geometry the cutting performance would have been many to one in favor of the CU/7. The handle on the C/U7 allowed for a hook grip around the end to be used in chopping which was far more secure than the same grip on the SOG, and far more comfortable than the TAC-11. The low chopping ability of the CU/7 was the only real drawback. It is outperformed multiple to one by the better chopping blades like the Ratweiler from Swamp Rat Knives.

A baton can be used to increase the chopping ability, however even when doing so, it performed at about 25% of the ability of a Tramontina Bolo in regards to time, On scrap, using a hook grip around the end, it performed similar at about 28 +/- 2 %, with a full grip around 20 +/- 3 %. A seven inch blade with a heavier dynamic balance could easily have 50% more chopping ability. In short, the chopping ability of the CU/7 would limit its wood working ability. However this problem is easily solved by supplementing it with a small quality folding saw.

Edge retention and cutting ability on 3/8" manilla hemp

As a stock test for edge retention, the CU/7 was used to slice through 3/8" manilla hemp on a plastic cutting board through a two inch draw. With the sharpness tested periodically on light thread and quarter inch poly. The cutting was initially done with the edge sharpened to a high polish, and the CU/7 could make 14 cuts before it required more than 60 lbs to cut the cord. Using a 600 grit DMT finish the cutting was repeated for three trials, the average result :

Fine DMT finish : NIB profile
# hemp cuts Thread Poly Hemp
  grams cm lbs
    0210 +/- 280.75 +/- 0.11N/A
    2240 +/- 211.20 +/- 0.1829 +/- 2
    6260 +/- 121.50 +/- 0.1131 +/- 2
  14 350 +/- 342.20 +/- 0.1938 +/- 1
  30 360 +/- 252.60 +/- 0.3238 +/- 5
  62 400 +/- 194.00 +/- 0.1755 +/- 7

The lifetime of the edge was increased by a factor of four over the polished edge. The blade responds well to steeling, seeing the performance increase back to almost 100%. However the edge retention is low with the steeled edge, a small fraction compared to freshly honed. Restoring back to optimal just takes 2-4 passes per side on the DMT rod. For comparion, the same cutting performed on a SOG SEAL (440A stainless steel) with the NIB profile, again sharpened on the 600 grit fine DMT rod is far behind.

The CU/7 cuts the rope about 50% better at the start over the SEAL, and can about cut four times as much rope before being blunted to a similar extent as the SOG. The much lower performane of the SOG is due to its thick profile which lowers its cutting ability. It it thicker and more obtuse than the CU/7. In particular the greater edge angle (26 +/- 1 degrees) also reduces the size of the micro-teeth produced at a given finish. The steel is also softer and will thus blunt faster by rolling.

durability

The CU/7 was frequently for light bone cutting, mainly working on chicken and turkey cutting cleanly around joints, cutting through them, and then rocking right through the bones, vertical pop can cuts were also attempted. A lot of very hard cutting was performed on very tough wood, including laminates and very seasoned scrap. Some of the wood was that hard it was splintering and breaking apart as it was cut. In all cases the edge resisted chipping, rolling and impaction.

The CU/7 was also used to split seasoned wood, driven through using full force impacts from a heavy baton (another piece of wood) intentionally chiseling through knots on occasion. The only drawback was that the sedge in the tip readily tore up the batons which had to be replaced every dozen or so rounds split. The edge showed no visible deformation let alone chipping, and the coating held up well. Both of these results are in direct contrast to the edge durability issues and quick coating wear seen on the Machax.

Modifications

The edge ground with a belt sander to an edge profile of 11 +/- 1 degrees per side when the edge was under 0.012" thick which went to 9-10 degrees up until the blade was 0.040" thick which was the start of the primary grind . Later a micro bevel was added during hand sharpening which thickened the profile slightly with a 13 +/- 1 degree micro bevel which started at 0.020" thick. The influence on cutting ability of the additional microbevel could not be seen.

Light utility work

On the manilla hemp, the modified CU/7 now only took 19 +/- 2 lbs on a slice, compared to 29 +/- 2 lbs NIB. The wood whittling ability was also increased significantly, the knife now only took 6.8 +/- 0.9 slices as compared to 9.9 +/- 0.4 before. Thus the cutting ability was increased in both cases by about 50 +/- 5 % . Such a large change in cutting abilility was readily obvious in use.

Brush work

Some scrap was chopped using a hook grip around the end of the handle for maximum power. The CU/7 now had about 48 +/- 5% of the chopping ability of the Tramontina bolo, a large improvement from its initial 28 +/- 2 %, showing the importantance of the edge profile. No edge damage was induced. The knife was then used to split a half a dozen rounds using another round as a baton. The chopping and splitting was repeated multiple times without any edge durablity problems. The edge doesn't even visibly roll enough to cause a significant glare of light.

Edge retention and cutting ability on 3/8" manilla hemp

The rope cutting was again repeated with the slimmer edge, first using a 600 DMT finish :

Fine DMT finish : modified profile
# hemp cuts Thread Poly Hemp
  grams cm lbs
    0210 +/- 380.90 +/- 0.16N/A
    2215 +/- 321.10 +/- 0.1931 +/- 2
    6280 +/- 111.40 +/- 0.1321 +/- 2
  14 310 +/- 111.60 +/- 0.1125 +/- 2
  30 340 +/- 161.60 +/- 0.3129 +/- 2
  62 400 +/- 112.85 +/- 0.1122 +/- 2
126 410 +/- 324.50 +/- 0.1725 +/- 2

Compared to the performance with the NIB edge sharpened at 600 DMT, the edge retention was about double. Note however that even after being so blunted the CU/7 with the modified profile cuts better than it did initially with the NIB profile. Thus the edge lifetime is much greater. The above was the result of one run which ideally should be repeated to confirm the behavior, however it is consistent with the performance of the Twistmaster with the same edge profile with is the same steel.

The cutting was repeated again with the edge finish left as formed by a 100 grit AO belt. The knife was sharpened once on a belt sander and another manually on the same belt as a consistency check. In each case a few passes were made on some canvas loaded with caulk paste to remove dirt and debris. The edge was shaving sharp and had large teeth about 75 microns deep, with smalled micro-teeth about one tenth the size. The average performance of the two runs :

Edge retention of the Becker CU/7 on 3/8" hemp with a 100 grit AO belt finish : modified edge profile
# hemp cuts Thread Poly Hemp
  grams cm lbs
    0160 +/- 300.65 +/- 0.06N/A
    2190 +/- 230.68 +/- 0.0919 +/- 2
    6210 +/- 111.23 +/- 0.0917 +/- 4
  14 255 +/- 191.35 +/- 0.0917 +/- 2
  30 270 +/- 341.32 +/- 0.0819 +/- 1
  62 310 +/- 231.90 +/- 0.1919 +/- 4
126 360 +/- 272.62 +/- 0.1519 +/- 3
254 400 +/- 193.45 +/- 0.0919 +/- 2
510 460 +/- 224.70 +/- 0.2625 +/- 1

The edge retention has improved over the 600 grit DMT finish by a factor of four this is due to the inherent greater edge retention of the more coarse finish as well as the increase in cutting ability also reduces the blunting effect of the cutting board. Even at the end of the above trial the CU/7 could still slice newspring readily on a slant. Under magnification, the large teeth are still present, but the micro-teeth have worn away. After ten passes per side on a strop loaded with CrO, the modified CU/7 again shaves readily and can push cut photo copy paper. Comparing the Becker to the Sorg Custom in D2 at the same finish, the D2 blade readily out cuts it many times to one however the Sorg blade has an advantage due to the lower force causing less of an effect of the cutting board, this doesn't explain the full difference of course and a direct comparison can be noted between the Twistmaster and Sorg when both have similar which also shows a many to one advantage of the Sorg which is to be expected as it is harder and much more wear resistant.

A graphical overview of the three different edge retention runs on the 3/8" hemp is presented in the following graph :

Photobucket - Video and Image Hosting

The run with the modified edge and coarse finish shows a lot of scatter early, which is to be expected given it is the average of only two runs, however looking at the late behavior in each trial it is clear that a many to ons advantage can be gained in slicing edge retention for more coarse finishes. The same behavior was seen with the Twistmaster with various grit finishes and an adjusted profile.

Edge durablity - hard impacts

With the modified edge profile, the Becker CU/7 was used to chop into a concrete block and some nails to examine the behavior of the edge in regards to high energy impacts onto hard materials. First the blade was subjected to 150 chops at full force in a concrete block, the concrete was shattering upon impact one out of every 4-5 hits. The impacts readily removed steel from the edge from impaction as well as brittle failure :

concrete impacts

Next, the CU/7 was chopped fifteen times into a 3.5" common nail, drove half way into a 4x4, with the knife chopping straight into the nails until they bent over or broke out. Each impact readily fractued the edge with little deformation :

nail impacts

In both cases the damage was limited to steel under 0.025" thick. With the edge reground to a steeper bevel of 18 degrees per side, the concrete block chopping was repeated and again the damage was limited to steel less than 0.025" thick. The more obtuse angle did however restricted the damage depth. In general, inclusions such as the nails in the above are far worse than chopping into a larger object. The pressure is much higher on the inclusions because the contact area is so low. In particular for the above, between the nails and the concrete, the difference is about ten to one.

This effect can also be seen in the concrete as the rocks are essentially inclusions. The sand and cement in the blocks can do little to damage a knife (outside of the brittle stainless alloys like ATS-34 [ref]), however the rocks are harder than the nails and can readily damage any blade. Fortunately since the sand and cement will fracture readily, the rocks are free to be broken out which reduces the stress on the edge.

Note the thickness of the edge makes little difference unless the edge width is exceeded in damage, which wasn't the case here. The edge angle is the critical geometrical factor in limiting the edge damage. Regarding the extend of metal loss, it would take hours of hand honing on the most abrasive hone to remove all the damage.

sharpening

As found on other knives with this steel, it was one of the better steels to sharpen, no complaints.

sheath

The sheath is once made from Cordura with a Kydex liner. It has a very similar construction to the ones from SOE and Blackhawk. However this one does not have the ability to transform to a low ride carry. It does however have one very nice feature, which the others lack, an elastic retention strap over the utility pocket. The blade is held securely, no significant rattle.

Summary

With the stock edge profile, the CU/7 had above average cutting ability for a knife of its class with no gross edge durablity problems and solid edge retention. The point strength is enough to handle even hard wood prying without damage and the durability of the knife as a whole was very solid. The only drawbacks were the slickness of the handle and abrasive nature of the grip holes. The chopping ability is low for its size and it is more of a utility cutting blade than something like the Ratweiler which much more powerful chopping. The coating also held up well, and while the blade did rust if left wet, this rusting didn't tend to excessively remove the coating, nor induce heavy pitting. As noted with other knives of the Becker line the handle is a bit slick and has low security and the holes in the grip can also be abrasive.

Comments and references

Comments can be sent to : cliffstamp[REMOVE]@cutleryscience.com or by posting in the following thread :




Last updated : Wed Jul 23 12:42:07 NDT 2003
Originally written : 03/11/2002
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