Bone cutting : Caribou legs

Cliff Stamp · Mar 28, 2003

The Becker Combat Bowie and Camp Tramp from Swamp Rat Knifeworks, were used to chop up a couple of Caribou legs which had been frozen overnight . The chopping was done at an angle of about 45 degrees, this maximises penetration and minimises stress on the edge. The cuts were done with a varying amount of force which resulted in the cuts ranging from two (near the hoof) to about twenty chops (close to the knee). The intended goal was to provide an edge durability benchmark to allow some comment to be made out the steel properties and geometry issues such as what kind of edge angle was necessary to resist damage, and how thin an edge could resist rippling. The results were unfortunately very high varianced. It was very difficult to reach a conclusion because of the significant variation experienced in cutting through one section of bone cut to the next, which was an issue mainly because there were only a few sections that could be cut, thus an effective average could not be well obtained. In any regard, the results :

The Camp Tramp cut through the first three sections of bone with no effect on the edge. However the next section of bone cut resulted in two chips being knocked out of the edge, one fracture was about 0.012" thick at maximum and the other 0.024". The next section of bone was again cut with no problems. In the region that the knife chipped the edge was ground at ~16 degrees per side and 0.060" thick. In reflection, the blade wasn't freshly sharpened and had been seeing very heavy use as of late, throwing and the like. Thus could have put the edge in a weakened state. As noted, the bone wasn't very uniform, it is possible that the one section that induced chipping was significantly harder than the rest. This kind of skew is easily solved by chopping a lot more bone and looking at the overall effect.

The Becker Combat bowie cut through all five sections of bone with no edge damage. After the cutting the blade still readily sliced paper as before. It didn't seem effected in any way. It was also a more powerful chopper than the Camp Tramp as it weighed more and is similar balanced. The edge is generally more obtuse than the Camp Tramp as it is ~18 degrees per side towards the tip, but does slim down to 15 degrees per side near the base, and that section of edge was used for the bone cutting as well. The edge is much slimmer than the Camp Tramp, going from about 0.035-0.038" thick. This would actually aid in making the edge more durable (speaking of damage which is less than the extent of the edge bevel width), as the thinner edge raises the inherent cutting ability at a given angle which makes for a smoother impact during a chop which reduces stress in a number of ways.

There is still some bone left and both blades will be given a full sharpening and the cutting repeated at a later date, hopefully with some fresh legs and other types of bone as well. I also have some large turkey legs and ham bones, and might be able to get some moose and caribou. In any case however, the Becker Combat bowie certainly did well, it could cut the bone near the hoof in one or two hits, and near the knee in about five clean hits, it generally took more as it is very difficult to get clean placement because of the extensive fracturing of the frozen bone.

UPDATE : note the comment below about the secondary edge bevel on the Becker bowie.

-Cliff

truck · Mar 31, 2003

Hey Cliff,
You chopped through a frozen Caribou leg bone with no damage to a Becker Bowie. Another guy up at the top of the forum chewed up a Brute's edge going through a 2x4. Please explain how such a thing could happen. Thanks

Minuteman · Mar 31, 2003

Hey truck, I'm the guy, and I was wondering the same thing myself! Until I learn otherwise I am chalking this up to quality variation.

Most of the time on this forum we see a test performed on a single copy of a particular blade. In reality we have no idea where that blade stands relative to the "average" blade to come off the production line. It might be the best or worst one ever made -- or right at the mean. The one thing we KNOW for sure is that there is variation in any manufacturing process. We just don't have any idea how big it is.

There is a way to find out this extra information, but it requires testing of a sample of a number of blades selected at random from the manufacturers production. If the sample contains the correct number of knives, based on the total number produced, then we can get an accurate picture of the overall consistency of a manufacturer's quality.

Unfortunately, neither Cliff nor I want to buy 37 knives to do a test!

switched · Mar 31, 2003

Yes well, I have always found Cliff to be rather unique. In saying that though, I don't mean to suggest I doubt his findings.

And...I must admit it has crossed my mind, what Cliff might do to our Crocodiles down here, frozen or otherwise.

Cliff Stamp · Mar 31, 2003

truck :

You chopped through a frozen Caribou leg bone with no damage to a Becker Bowie. Another guy up at the top of the forum chewed up a Brute's edge going through a 2x4. Please explain how such a thing could happen.

I also had a Machax from Camillus take damage readily on wood chopping, denting and chipping, and saw two gross failures with Patrol Machetes. The performance of the steel seems to vary widely from blade to blade. The current Bowie has a much more durable edge than the other Becker blades I have used. This weekend it was used to split about 100 piece of wood, some with knots so thick it too 3-4 full power hits to chisel them straight through (this isn't the optimal method - I was just looking at a worse case senario). This combined with the bone cutting resulted in one small dent to the edge, about 0.15 mm deep and 1 mm long. It could be steeled out to about half that size. The edge was still aggressive and could catch on the thumbnail, but had lost a significant amount of paper slicing ability. Sharpening would be a few passes on a rod, nothing serious.

*I should note that the CU9 has a slight secondary edge bevel ~0.2 mm wide which is significantly more obtuse than the edge bevel specifics listed in the above. This explains why it retained so much sharpness after the bone cutting. This will be removed before the cutting is repeated.

-Cliff

truck · Apr 2, 2003

Okay, I'll buy the theory of variation. What it means in the real world is that I won't buy any Beckers because luck, and myself, don't ever seem to walk on the same side of the street

Cliff Stamp · Apr 2, 2003

That is understandable, however the customer support from Camillus is first rate. If you did have a problem you would be taken care of .

-Cliff

Minuteman · Apr 2, 2003

What it means in the real world is that I won't buy any Beckers because luck, and myself, don't ever seem to walk on the same side of the street

Truck, you and I must be related. I aways end up becoming overly familiar with the people who work in customer service departments.

Cliff Stamp · Apr 7, 2003

The Caribou cutting was repeated this weekend. Unfortunately the legs were left out of the freezer accidently so it was not an exact duplicate of the first run where the legs were frozen. Both knives were sharpened before the cutting. The Becker Bowie had the obtuse secondary bevel removed with use of a coarse waterstone, and the Camp Tramp was reground on a 100 grit AO belt to remove the chips. Both were polished with waterstones and finished on CrO, and could easily push cut flimsy glossy paper with just a hint of a slice to start the cut, and could shave decently well.

The blades were each chopped into the legs at full force a total of 25 times. There was no significant difference in how the bone responded to the chopping as compared to when it was frozen. It again could not be cut using a wood chip clearing technique, but with heavy hits could be directly sectioned in just a few chops. It would for example take much longer to cut through a similar sized piece of spruce, or any medium density wood.

Neither blade took visible damage during the cutting, the chops were again made at approximately a forty five degree angle into the bone to minimise stress. After the chopping both blades could easily remove the skin from the legs, cut away tendons and do other fine cutting. Both would still slice the glossy paper well, but neither would shave beyond scraping the occasional hair.

Under magnification, there was one spot of damage on the Becker Bowie about 0.4 to 0.6 mm deep and one mm long. There was also a rough spot where the edge had impacted / fractured to about 0.1 mm deep and a few mm long. The Camp Tramp showed a similar rough spot slightly longer, and had four chips the size of the one on the Becker Bowie. A light stropping on some CrO loaded leather (10 passes per side) and both blades were push shaving sharp, except for the few mm of described damage .

On reflection, the Camp Tramp had large scratches in the edge from the 100 AO belt which would have weakened its edge, these should have been completely removed in order to place it on equal footing with the Becker Bowie, in any case the durability was much closer this time around. On examination of the cutting board, the most likely cause of the damage was bits of bone which were driven into the 4x4 and thus formed debris that the edge would slam into and twist around.

In short, the previous round of heavy damage on the Camp Tramp doesn't seem to be its expected behaviour, and was as expected the result of very recent heavy use while it was on loan. The Becker Bowie did very well, and the initial cutting on the frozen legs showed the huge benefit of even a very small more obtuse secondary bevel which can add significant durability with little loss to cutting ability.

-Cliff

Yojimbo · Apr 8, 2003

Great post Cliff!

Was the secondary bevel on the BK9 a factory thing or was is it something Andrew Lynch did while he tested the BK9? Could you also explain how a secondary bevel would make such a difference? Does it aid in strengthening the primary edge?

Cliff Stamp · Apr 8, 2003

The secondary bevel Andrew applied with the Sharpmaker. The reason that it made the edge so much more durable was because it was heavily more obtuse than the factory edge grind which was only ~15 degrees per side. Since the damage induced here was only very slight, a small fraction of a mm a similar sized secondary bevel was all that was necessary to give the edge the actual functional strength of a full 20 degree bevel. Because the secondary 20 degree bevel was very narrow (you could not see it by eye) it didn't significantly reduce the cutting ability.

Note this small of a secondary bevel would not help much if the edge was whacked into a piece of concrete of similar, as then the damage is likely to be much more extensive, and denting / fracture could be from 0.01 to 0.04" thick. In general you need a secondary bevel of similar thickness as the expected damage, which in this specific case would mean practically the whole edge would be ground at 20 degrees. A small more obtuse bevel would help but not eliminate the damage completely as it did in the above.

-Cliff