Home › Forums › Friends of FOC › 25 Degree angle of cut?
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I have just read Ashby’s 34 reports:shock: and see much comparative analysis to best means of gaining pentetration given to subjects of Foc, BH design, arrow design, total arrow mass….but cannot find any evidence to why 25 degrees angle of cut is recommended as superior to any other angle,
provided the broadhead is razor sharp at all angles.
I have received expert testimony to state many angles of cut can be made equally sharp, so why is 25 degrees recommended? At what other angle is the Single bevel BH not going to perform as well? I do use a KME sharpener, so I am able to obtain a controlled angle. Using 25 degrees with this type of sharpener necessitates grinding the ferrule on my Outback Supreme BH’s to create cut edge clearance and this compromises structural integrity….Not sure if most 3:1 ratio BH’s have a problem with ferrule clearance using a KME and similar style of sharpener.
Is 30 degrees just as effective in penetration? That would help clear the ferrule. Double bevel heads certainly cut with a greater total angle than that(to my experience). Ashby used such good scientific method, there must be a reason why 25 degrees is stated.
Thanks
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While am in no way any kind of authority on sharpening or edges, the only thing I can think of would be that the 25 deg would provide slightly less resistance when cutting tissue.
I have recently acquired the skills I have been seeking for years, to sharpen my knives and broadheads to razor edges. That came from help on the above video and from a book I have on the subject. In the book, one of he points he stresses is getting sufficient “relief” on the edge. In the authors opinion, most knives come from the factories with a sharp edge but a very sharp angle bevel right behind it. This limits the effective “slicing” effect of the edge. He says to run your fingers from the edge back towards the back of the blade, straight away from the edge, not along it. You should net really be able to tell when you leave the edge and get into the blade, so little to no angle.
To me it kinda makes more sense to think that a wedge type edge, like how everything I ever see sharpened has, if more suited for chopping through tough stuff, rather than slicing. But when the very thin edge is ground with a very smooth relief from the edge back, the blade just slices through so much easier.
On my knives that has been absolutely true. The edge will not take any chopping action, so if that is the intent, it’s best to have the more triangle style bevel, it would be more durable.
I hope this make sense, and like I said, I am NO authority, at all, just a newby with some observations.
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Hi OpenSky1, and welcome to the site. I am moving your thread to the Friends of FOC forum, where Ashby studies and findings are discussed. Dr. Ashby pops into the forum when he can, and David Petersen is usually pretty active there, but he is off the grid this week. Hopefully, someone else in that forum can answer your question.
Take care,
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OpenSky1 wrote:
[u] I do use a KME sharpener, so I am able to obtain a controlled angle. Using 25 degrees with this type of sharpener necessitates grinding the ferrule on my Outback Supreme BH’s to create cut edge clearance and this compromises structural integrity….Not sure if most 3:1 ratio BH’s have a problem with ferrule
Welcome to the forum, OpenSky. I use single bevels, and a KME to maintain them. What I found was that if I set my KME exactly at 25deg, I was less than satisfied with the results, and it seemed to take more effort than normal to get an edge. Also, as you mention, depending on the type of broadhead you are using, you might also experience some interference with the ferrule.
So then I had a great talk with Ron from KME (“sharpster” on this forum”) a while back about this, and he recommended a slight increase in the angle above 25. I made this change (to about 26.5 deg) and it made all the difference. I was able to get the edge I wanted quickly, with minimal effort.
I believe Ron did a little tutorial on using the KME for single bevels here a while back if you do a search.
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Wish I had your skills using these forums to better respond to all. Thanks to you both for the replies. I did not see any video/link attached to the reply by Smithhammer? I understand the concepts you mentioned. Handrifle, are the BH’s you are using a 3:1 ratio and you have clearance at 26 degrees? Mfr? I would like to continue to use the KME instead of all the freehanding many choose to do. I am a skilled tradesman and there is a big difference between freehand and the result obtained from a jig. That KME puts the angle spot on. Problem was the Outback Supreme Single Bevel was cut at factory to 32 degrees. I had to cut ferrule down drastically to obtain 25 degrees stated using the KME, which was how my question of WHY IS 25 DEGREES ‘BEST’ started. Is there any evidence that an equally sharp 30 degree angle of cut on same BH would penetrate any better/worse?
I have been in personal contact with Ron from KME(awesome customer service, willing to do anything to help), and his was the personal testimony referred to. It was his tutorial that suggested grinding the ferrule and also mentioned was that a few degrees of angle or a lot makes no difference to sharpness. Ashby studies give cause for concern to not compromise integrity/strength,(so I shouldn’t grind a ferrule to nothing, which is about what I had to do to achieve 25 degrees on the Outback Supreme if using the KME) and that is why I do not want to grind the ferrule at all if not needed. In other words why 26 1/2 degrees instead of just raising the jig further to 29 or whatever other number you want to put in there.
I just am looking for evidence of studies, if any exist, that show a THRESHOLD to angle of cut where a BH penetrates best. I am assuming Mr. Ashby believes this to be 25 degrees. Still wondering why from evidence?
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Mine are a 3-1 ratio, but my jig isn’t a KME and the angles don’t match, so I free hand it.
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Hey guys!
I have had the same problem myself with Tuffhead 225s and the KME. There is no way to get a 25 angle without grinding the ferrule so I just moved it up to 30 degrees. I also use the 200 grain grizzly BHs and no problem getting them at 25 degrees with the KME but the blade is wider. I would be interested in seeing if there is any measurable
difference b/w a 30 and 25 degree angle since it doesn’t seem like much.
I do find the grizzly BHs a little easier to get crazy sharp though. Going hog hunting in the morning so maybe I’ll get a chance to test both:D
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DaveT wrote: Hey guys!
I have had the same problem myself with Tuffhead 125s and the KME. There is no way to get a 25 angle without grinding the ferrule so I just moved it up to 30 degrees. I also use the 200 grain grizzly BHs and no problem getting them at 25 degrees with the KME but the blade is wider. I would be interested in seeing if there is any measurable
difference b/w a 30 and 25 degree angle since it doesn’t seem like much.
I do find the grizzly BHs a little easier to get crazy sharp though. Going hog hunting in the morning so maybe I’ll get a chance to test both:D
did you mean Tuffhead 225 instead of 125? I cannot find a Tuffhead 125.
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I can’t recall if I read it or Doc Ashby stated it to me, but the 25 degrees proved in his testing to be the best combo of effective cutting and edge maintenance. A higher angle is tougher but not as sharp, and a lower angle is sharper but too thin to maintain that sharpness if it impacts heavy bone. 25 degrees thus is a happy compromise.
On the KME sharpener, Ron/Sharpster told me that the best you can do with a guide on a jig like that is a close approximation, while most 25 degree heads today, like the Tuffheads and other top-end single-bevels, are machined at precisely 25 degrees. So you simply eyeball the jig angle to match the blade angle and there you go. Take a few swipes with a fine stone and inspect the edge to see if it’s contacting dead-on, or high or low, and re-adjust. I do the same with my knives … adjust the jig to match the blade bevel angle, check the contact with a few strokes, readjust as necessary, and away you go. It takes only seconds.
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All good feedback. Thank you. The question still remains if a 30 degree angle, which I am suggesting since use of KME or similar product would not require grinding of ferrule, shows a measurable loss of penetration vs. a 25 degree angle, or other.
I have done extensive research, and observed many guys just use a freehand technique, and looking at their vids, BH’s are extremenly sharp. My concern over freehanding is the subject interwoven in this chat about durability to the angle. If 5 or 10 degrees in angle is not relevant to penetration, assuming both are equally sharp, than freehanding is an acceptable option in my opinion. If 25 shows a marked change than 30 in penetration, then to freehand is a bit more risky, especially for a less experienced sharpener as myself. Don’t get me wrong, I am a skilled tradesman, but I know for a fact that an inexperienced sharpener like me can replicate an angle spot on with a KME jig, with far greater accuracy to angle of cut than the most experienced sharpener using a freehand technique can. And to be completely honest, to date my BH are no where near as sharp with me using a jig, as those freehanding on vids. I have seen.(They are sharp but not shaving completely clean! I was of the former understanding this was good enough. Reading Ashby’s studies I now see differently. I am doing my best to improve on this skill).
Again appreciate all input. Fred Bear and archery forerunners have successfully taken game. We need not complicate the issue. [u]The purpose of my post, is I am inclined to put all odds in my favor.[/u] Had overheard 3 fellow hunters chatting at another archery shop here in SW Wisconsin about the recent archery deer season, and all 3 have hit multiple game this year without recovery. 1 of these hunters was the shop owner! The problem was a lack of ethics by no remorse expressed(quite the opposite)to a failure to their system. Ashby studies show an alarming frequency to this problem, and much is preventable. So I am just gathering info. to help better myself and then be able to provide knowledgeable info. to those I come in contact with.
Without having the unique circumstance to test on the large quantity of game Ashby was presented with, the average Joe like myself is unable to answer the question I posted about why 25 degrees is ‘best’. Hence my reaching out to a national audience.
In the meantime I will apply the great source of knowledge already verified to better my odds of ethically harvesting game. Hope you all do the same. Good hunting.
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I just had a phone conversation with Dr. Ed Ashby to address “Why 25 degree angle of cut”. He has a health issue which prohibits him from using his arm, and with his permission, I am thus forwarding a summation of our conversation for the benefit of all.
To start, whether the BH was 25 or 35 degrees, assuming a similarly sharp angle, it is suspected to have no discernable difference in regards to PENETRATION. No scientific study was done to verify this hypothesis: a study of this type is suspected to require 1,000 shots under a controlled study to reach any meaningful conclusions.
Next, 25 1/2 degrees was confirmed to be Dr. Ashby’s preferred angle of cut. I will address why Dr. Ashby came to this conclusion, and how 25 1/2 is preferred to an angle such as 35 degrees for example.
WHY – The thinner the cutting edge, the greater the mechanical advantage a BH gains with regard to severing the blood vessels: less pressure is required to sever the blood vessel with a thinner edge. Unless pneumo thorax occurs(my insert), an archer/arrow kills with hemorrhaging. [A cell when cut, wants to coagulate through a series of reactions by blood plasma enzymes and proteins…prothrombin…thrombin….fibrinogen….fibrin which attaches to the tissue tags at the edge of a cut, causing coagulation].
HOW – Simply, through much independent trial and error, any thinner of an angle of cut than 25 1/2 degrees was causing an edge roll to the BH because it lacked durability and thus defeated the purpose of WHY. It is emphasized that a minimum Rockwell hardness of 52 is required to shoot an angle as small as 25 1/2 degrees. Assuming a softer metal is chosen, this requires a greater angle to BH, so integrity is not compromised(Dr. Ashby did not recommend a softer metal- 52-57 is recommended hardness range for the compromise between durability and brittleness).
In confirmation to Dr. Ashby’s conclusions 1).Larry Hanify, an engineer with Abowyer Broadhead Co. came to the same conclusion from his studies. 2). Bacon skinners all use 25 degrees single bevel for the perfect balance between sharpness and durability. 3). Tire cutters all use 25 degrees also.
One last note about methodology of obtaining the angle of cut. Dr. Ashby said it is critical to both penetration and hemorrhaging for the edge to be refined. A file is not good enough, even a smooth edge file. File burrs cause extra tissue tags to form, and these increase coagulation.
It is his educated opinion a file and a subsequent refinement using a window edge,coffee cup or similar is not refined enough. They may cut paper and rubber bands well, but on live cells, nothing bleeds as well as a refined edge. Dr. Ashby is quoted as preferring to prepare for the worst case scernerio, to put all odds in his favor, and I am in complete agreement with this philosophy.
Thank you Dr. Ashby for sharing this knowledge to better the Bowhunting community. Saying a prayer for a speedy and complete recovery to your health issues.
Good hunting to you all.
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Dave and Smithhammer are correct in there assessment of sharpening the single bevel at 25 degrees.
I have copied and pasted a letter from Ron at KME that explains why the KME knife sharpener may not line up with the 25 degree bevel on the broadhead.
Confused about exact sharpening angles?
In a recent discussion on proper sharpening angles and use of the KME system, one of our most experienced friends questioned …
“Just now I touched up my 6 Tuffheads for the hunt, using my KME knife sharpener. According to the scale on the sharpener it was set at 25 degrees. But in order to get the stone to lie precisely parallel to the bevel on the heads I had to raise it up to one mark below 30 degrees – 28 or 29 I reckon. So is the scale off on the jig, or the bevel in fact greater than 25 degrees, or something else I’m missing here? Just curious. In any event those heads are sharp and one has already drawn blood, my own.”
A quick response from Rom Schwartz at KME explins the details…
“Figured I’d share this drawing to help explain why Dave needs to set the shapener to 29 degrees in order to match a 25 degree bevel.
The angle scales on all clamp-on sharpening systems are relative, not absolute. This is because there are multiple factors that influence the actual sharpening angle.
We can adjust the angle by raising/lowering the bearing guide but the distance the blade extends out in front of the clamp has just as great an influence on the angle too.
This is just basic geometry and there’s no escaping it.
The best way to match an existing bevel is to color the bevel with a permanent marker, eyeball the angle as best as we can, then take just a few strokes with a dry stone to see where the ink is being removed. If the ink is being taken from the shoulder of the bevel but not from the cutting edge, that means the angle is set too low. If we’re removing ink from the cutting edge but not from the shoulder, that means the angle is set too high. Micro adjust till the ink is being removed from the whole bevel and you have found the correct setting for that particular knife or BHD. Note: it’s preferable to have the angle set a bit too high than it is to have it set a bit too low. This way we’re certain that the stone is contacting the actual cutting edge.
Dave when sharpening Grizzly El Grandes with the knife sharpener, I find that I need to set the sharpener at 27 degrees even though I know that the factory bevel is ground at 25 degrees. The angle scale may indicate that I’m sharpening the Grizz at 27 degrees but in fact it’s actually sharpening at the same 25 as my original “factory” grind.
Sorry for the poor quality of the sketch but I think you’ll see what I’m talking about. Thanks, Ron
Ron Swartz
KME Sharpeners
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