Degrees of Rotation of Single Bevel Heads

[IronCreekArcher]

#7059

On a pass-through, soft tissue (i.e. between ribs) shot how many degrees does a single bevel rotate from start to finish? Conversely, on a bone impact shot (i.e. shoulder or ribs) how many degrees of rotation is there? I have read the Ashby reports and vaugely remember a mention of this but can’t remember specific details. Any help would be greatly appreciated.

[David Petersen]

#57906

Dan — I am jumping in here only because Dr. Ashby has been on the road and off the airwaves for some times now, and I doubt anyone else will respond, though I hope they do. I’m not at all sure your question can be answered as asked, or that knowing the precise degree of turn really matters beyond curiosity. I do recall Ashby reporting that the rate of “spin” increases once flesh is contacted — that is, in meat the single-bevel turns more rotations per inch than it does in flight. Variants controlling the rate of turn would include density of tissue and broadhead design, especially degree of bevel and width/thickness of the bevel shelf. The thicker the blade, the wider the shelf will be at a given bevel angle, thus the more torque. A nonscientific but interesting home experiment is to shoot different single-bevels from the same arrows and bow into the same foam target to compare penetration and, best you can, degree of spin before they come to a stop. The most revealing of all is to shoot a good single bevel alongside a double bevel identical blade. Aside from differences in penetration it’s revealing when you pull the arrows out of the target that the double-bevel pulls straight out while the single-bevel “screws” out. Finger details aside, I have seen for myself what a good single-bevel will do with elk, both soft tissue and heavy bone, and it works. For a long time I’ve said that I thought the best s-b for the money was the Brown Bear. But now they’ve increased price to the point I’ve lost interest. Fingers crossed that the new/forthcoming Eclipse Werewolf will perform as good as it looks and shoots (I have a single prototype head I’ve been playing with, and managed to slice my palm on the sharpened back edge, as it came from the factory. No other production s-b I know of comes that sharp.) Which goes way beyond your question without even properly answering it. 😳 Congrats on finishing your degree. Dave

[IronCreekArcher]

#58095

The interest comes from reading the article in the TBM about sharp heads and how the rotation of single bevels encounters more tissue as it rotates. I am trying to figure out what the increase of tissue contact is as a percentage given the distance of penetration and amount of rotation. I may be chasing the impossible as the variables are many but; I am at least hoping to be able to quantify the two broad categories of soft tissue impact and hard bone impact. I talked to Blake today about the new Werewolf broadheads he is coming out with and it turns out it’s the creation of a design we talked about together a few years back. I am glad to see him moving forward with this idea. He is going to send me a couple too torture test, we should compare notes when my testing is complete. I will also post my findings on here along with pictures. Hey I have an idea; we should have a single bevel broadhead feature of the month or bi-monthly or whatever. A series of tests could be conducted on a given head, conclusions could be drawn about the pros and cons and we could post it here for others to read…just a thought. Thanks for the help Dave…

[Mark Turton]

#59037

Hi Dan, Dave, this subject fascinates me, if you can give me the angle of the cutting edge from the center line I can calculate the distance it will travel for one rotation, bit like rifling in a barrel.

Some time ago I tried to work out the path of a single bevel broadhead as it passes thru meat but that defeated me, it also defeated the ghouls at a medical company we supply tools to so I did not feel so bad. My guess is that once the broadhead enters flesh and experiences uneven pressure on its faces it prescribes a helix and this is what crates the huge amount of tissue damage, unfortunately I’ve only seen pictures and not had the opportunity to roll up my sleeves and dive into a wound channel.

[David Petersen]

#59107

Where is the Doc when we need him? He is deeply informed regarding anything to do with math, physics, engineering and no doubt could answer this fast and easy.

For now, let’s assume a 25-degree bevel, as that is quickly becoming the standard for single-bevels. But don’t such variables as blade length and width figure in? For example, wouldn’t the amount of tissue contact and slicing by the rotating head differ from, say, two heads at 1-1/8″ wide and 7/8″ wide? This seems impossible to calculate mathmatically short of working out an entire table of variables. But then, I can barely balance my check book, and I write very few checks. Have fun …

[IronCreekArcher]

#59218

I hear ya there Dave…almost thinking about giving it up at the moment…

[turok]

#60571

I hate to say this, but maybe we need to borrow a few tricks from the gunners and shoot a s/b head into some balistic gelatin and trace the helix; the path would be obvious in that stuff.
Even better would be to high speed film it penetrating the gel. That would show exactly what we need to see.

Mike

[IronCreekArcher]

#63747

I have thought about doing this Mike but cost of the gelatin is a bit prohibitive at the moment and I also have to figure out how to simulate bone impact with the gellatin as well. I have found some interesting tests on youtube from various broadhead mfr’s that could be duplicated with the single bevel heads but again cost becomes a factor…

[Homer]

#63896

IronCreek — while I applaud your desire to help sort out all this confusing tech stuff, at least to your own satisfaction, I keep thinking bout something Ashby said a way long time ago, about there not being any synthetic way of imitating with synthetic target materials the amazingly complex variety of what can happen when an arrow hits an animal that may be turned this way or that, shooting up for down angle, running or standing still, hitting no bone or small bones or broadhead-busting bones. And so on seemingly forever. That’s why he, Ashby, wound up shooting arrows into freshly dead animals at every possible angle and etc. While some archers I understand shy away from shooting a fresh-killed animal’s body full of arrows for “science,” I can’t see a better way to fiture it out. Other than keeping absolutely honest and detailed records on every aspect of every kill we make. But Ashby has already done that for us, over some 30 years! I too am a tinkerur and enjoy the experiments as fun, and thus have no patience with the “if it works, why try to make it better” caveman mentality. But when it gets down to shooting into expensive ballistic jello with no bones and all such … I think maybe we’re better off just experimenting with what among all of Ashby’s research findings say works best, to see what among it works best for us and our set-ups and game, etc. Our shared problem is that the off-season lasts way too long for those of us “only just want to hunt.” My own problem as I get older isn’t what gear to use — I have that figured out for myself — but making the shot under pressure. It’s one thing to yap about “pefect arrow placement’ as the answer to everything. But another thing entirely to make those perfect shots, every single time. To paraphrase what someone said here before — well, I forget what they said! All that matters is that we have fun with it and do everything we can to make clean kills even when things aren’t perfect. I once knew a girl named PollyAnna, but even she got old and wrinkled. Homer

[Mark Turton]

#9297

2 hours of calculations and all I proved is that ‘I know nothing’
My new area of fascination ‘computational fluid dynamics’ and what have I learnt ‘I know nothing’
This is way more complex than ballistics relating to firearms, closest I have found after hours of trawling the net is that a broadhead will behave more like a wind turbine than anything else I have found.
What I have learnt is that no matter what the broadhead will do you also have to consider all other components the biggest variable will be fletchings and that makes most of what I was trying to do worthless.
Homer is correct in quoting Doc Ashby, modeling a bradheads flight bears very little relationship to what happens when it contacts meat and bone.

Free software download of http://www.openfoam.com may be interesting.

Mark.

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