Ashby interview-thoughts on carbons

[KSdan]

I was reading Ashby's interview last night and he does not sound overly encouraged by carbons (apparently too weak on bone).  Any thoughts??  I really like the way they shoot.  Are some of you guys footing them with aluminum or something else to offset this weakness?

I also wonder about the broadhead adaptor.  He says aboslutely stay away from aluminum.  Is there steel out there and what do they weigh?

Thanks in advance for your thoughts. .

Dan

[Dr. Ed Ashby]

Dan,

Read through the 2007 Updates, Parts 2, 3 and 4. There's a lot more information there than in the TBM article. They will answer a lot of your questions.

At the moment, yes, there are some problems with carbon shaft strength during heavy-bone and angular bone impact. We're working hard on addressing that problem. For now, the most durable carbon setup easily available is a long brass insert with a steel broadhead adaptor.

Also check out the 75 gr. steel adaptor thread here on pow-wow. It appears that not all the steel adaptors are created equal. Oh, BTW, they come in 75, 100 and 125 grain weights.

It is hoped that an Internal Footing will soon be available, if the 'comercial prototypes' come through testing with performance like the 'test prototypes' did. (That info is in Part 3.)

Use of both high MA broadheads and/or single-bevel BH's has demonstrated a marked reduction in carbon shaft breakage too (when with brass inserts and steel adaptors). That info is in Part 4.

Not all the carbon shafts are equally durable on impact, either. The Grizzly Stik has shown the greatest durability so far, but they are not necessarily the shaft for everyone. However, they are great for those that like using them, and don't mind the bit more attention to tuning they take (they have a definite 'spine side', and all length adjustment has to be done from the point end of the shaft; so they take more effort during tuning).

Hope that helps give you a starting place.

Ed
TGMM Family of the Bow

[DesertDude]

Dr. Ashby,  I have a question then...if you take the 100gr brass insert, 100gr steel adaptor and a 190gr BH your starting with 390gr+ up front. This is all before you add the shaft, fletching, and nock. Is there any issues to consider when starting at this point?

[Dr. Ed Ashby]

Not much Mark. My 'most often used' is like that, except with a 125 grian adaptor; for 415 grains up front. I've used that point weight (or very close to it) on everything from the full range of Grizzly Stiks to GT Lites, Axis and Beman shafts. Lighter the shaft, higher the FOC. All tune beautifully.

I've gone even higher, using the 258 Grain Pro Big game instead of the 190 Grizzly. That's 483 grains up front. Still works the same, just more FOC.

Now, none of that is to say that anyone HAS to use that much weight. I'm just pushing the weight to see the effect of the incrased FOC. I've set up Extreme FOC arrows on GT Lites that weighted in right at 650 grains total mass; and some on some on the Axis (with aluminum inserts) that were just over 500 grains.

All testing indicates the more FOC you can get of a carbon shafted arrow, the more benefits one sees - whenever they stay structurally secure.

BTW, I was Air Force. Got sent there under the Doctor's draft - no choice. However, my family has always been Navy. Big age span in my family. I had one brother at the Battle of Midway. Lied about his age. Retired when he was 36!

Ed
TGMM Family of the Bow

[KSdan]

I have read a lot but still not sure what a "high MA" head is??  I wish I could see a list. . .

By the way, two years ago I went with carbons (after 15 years of 2219 alums) and while I see better tuning, trajectory, and accuracy, I have witnessed a loss in penetration and one bad experience with shoulder bone- the carbon shaft actually snapped off about one inch from bop. (below the insert).

[Dr. Ed Ashby]

Dan, mechanical advantage is just that; application of the formula(s) for the mechancial advantage of an inclined plane and that of a wedge; from basic physics. It's a ratio of how far a load is mover to the height it is lifted.

For example: For a straight tapered wedge 3" long (along one edge of the slope) and 1" wide (total width at the back), the MA is 3.  If that same 3" long slope has to lift (spread) the load 2", then the MA drops to 1.5. In this over-simplified example, you can think of the 3 MA as reflecting a single blade BH 3" long, with a 1" cut width. The 1.5 MA would be the MA for a 4 blade BH 3" long, and with a total cut width of 2" (1"x1").

MA also reflects the ratio of the 'work' (as defined in physics) done with the force applied. A 3:1 MA implies that the application of "X" amout of force allows you to accomplish an amount ot 'work" equiling "3X". You multiply the force you have available by the MA to determine the total amount of work you can accomplish. That's about as simple an explination as I can think of at the moment.

There are other factors in BH design that are important too; resistance factors, such as ferrule profile, blade vents, and rough surfaces. However that should give you some idea what we're talking about.

If it helps, the MA for a 190 grain Grizzly is 2.75. For the Modified Grizzly (same length, but with the width narrowed from 1.125" to 1", and with the slope of the edge changed, is 3.25.

Anything above a true MA of 2.6 reflects a BH that is darned good at getting through all tissues. The 160 gr. STOS is just barely below 2.6 MA. Most BH's of the Eskimo or Magnus II class have MA's in the 1.8 to 1.9 range, and no multiblade available that has a MA anywhere near those. Some BH's with high blade MA lose a lot because of the ferrule profile, or other less-than-ideal design features.

In a nutshell, the higher you BH's MA, the more 'work' your arrow is capable of doing with whatever force it impacts with. Same arrow at the same force: use of a 3.0 MA BH allows it to acomplish twice as much work as one with a BH having a 1.5 MA.

Hope that helps a bit,

Ed
TGMM Family of the Bow

[Jeff Sample]

Dr. Ashby,

A question about increased/extreme FOC: is there an advantage as well for POC or other wood shafts? Everything I've read or heard about this has related to the relatively light carbon shaft. I would think that putting that much weight on the end of a POC shaft would require a significantly greater spined shaft to deal with the reduced "dynamic" spine as a consequence of more weight up front, particularly out of a bow that is less than center-shot. I assume that carbon has different properties that make it flex less upon release, and that because of their narrower diameter, most people are shooting them either center or less than center out of recurves and some long bows.

Thanks!

[KSdan]

 Thanks much- I think I got it.  Sounds like the original griz 190 can hardly be beat- all other things being equal.  

Now if I can learn to sharpen the blasted things      :confused:  

Dan

[Jeff Sample]

PS - Also, what makes a single-bevel blade better?

[Dr. Ed Ashby]

Jeff,

Yes. My favorite wood shaft of all time was the original Forgewood. With its differential compression, it had high weight forward. With the Grizzly it had an FOC just over 19% - bringing it into the Extreme FOC range. That is, very likely, one major reason I had such great success with them - I just didn't realize the importance at the time.

If you check through some of today's very active threads on TG, you'll see several folks are working towards Extreme FOC from wood shafts - and at least one (possibly 2) BH makers are looking at some heavier glue-mount BH's (250-300 grain range), aimed directly at reaching Extreme FOC with the wood shafts.

Many 'primative arrows' reach(ed) Extreme FOC; among them are the footed cane Oriental arrows and some original American Indian arrows.

Of all shaft materials, I've had the most difficulty getting good Extreme FOC flight from the aluminums; and carbons are the easiest.

Many of my bows are far from center-shot. Some even have peg rest. Some are near center-shot. Extreme FOC can work for all.

Ed
TGMM family of the Bow

[Dr. Ed Ashby]

Jeff,

Find the 'Why Single Bevel Broadheads" article. Go to Main Forums, and down to the Dr. Ashby Reports forum. You'll find it there. Probably more about the 'why' of single-bevels than you ever wanted to know!

Hope that helps,

Ed
TGMM Family of the Bow

[Ray_G]

Dr. Ashby,  I have been reading all of the posts here related to EFOC, single bevel, etal.  I have just recently acquired a traditional bow after a 35 year hiatus from using them and it was a youthful, limited use, I might add.  

I am curious about your statement regarding "they have a definite 'spine side'," in relation to GrizzlyStiks.  I just received some Sitkas and have yet to tune them.  43# @ 27"

How is the "spine side" determined?  Is this relationship the same or easily identified in these arrows?  I appreciate your efforts for the good of all bowhunters.

Ray

[peter c iacavazzi]

Hi Dr. Ashby

I have been following this thread as well as any thread where I see you're actively involved. I have also firmly committed to going with an extreme FOC set up this year. I think all agree that your research and data clearly indicate that a broadhead with a high "MA" and an extreme FOC combined with a properly tuned shaft and a single bevel head really is the best choice for any big game bowhunter.

Here is my question: I have spoken with many guys here in my home state of Montana and across the country. I am finding that most guys would love to switch over to a single bevel head (Grizzly, Zwickey etc) But the overwhelming contention is that they are extremely difficult to sharpen and to create the "Tanto" tip you prefer.

In fact jokingly one very well respected bowhunter here in Montana calls the single bevel head "Code for Impossible to sharpen".

All that aside. Do you have any advice for the many guys (myself being one) that would like to make the switch over to a Grizzly or similar head but that are having a difficult if not impossible time arriving at a head that would be accepatable to you?

Thanks for any input or advice and on behalf of the bowhunting community: Thank you for your wonderful and indepth work!!

Respectfully, Peter Iacavazzi

[Dr. Ed Ashby]

Ray,

Ed Schlief usually has a little blurb he includes about how to find the 'stiff side'. He recommneds you just place one end of the shaft against a table and hold the other end with one hand; with the shaft at about a 35 to 45 degree angle. Then you flex the shaft with your other hand; rotate the shaft a bit and flex again. I'll admit that this works very well ... once you get the hang of it. I can bracket in, going back and forth from side to side of the point that feels stiffest; and get darned close to spot-on for the stiffest side. But it did take a while for me to get the 'touch' of doing it.

Of course, one sure way is to put them on a spine-tester and rotate the shaft until you find the stiff side ... if you have access to a spine tester. Alternately, here's the po'boy way.

Drill a hole in an upright (a block of 2x4 attached to the workbench works). Make the hole just large enough to accept the front of the shaft. The hole should be placed such that the shaft is held horizontially; parallel to the edge of your workbench. Clamp or tape a ruler vertically just back of the free end of the shaft (or a piece of paper or cardboard with parallel horizontal lines will work just as well). Now attach a weight, sufficient to flex the shaft a few inches, to the free end of the shaft. The exact weight doesn't matter, just so it is enough to bend the shaft. Now sight on a level with the shaft's free end and note the amount of bending the shaft shows. Next, rotate the shaft and again note how much it bends. Keep doing this until you find the spot where the shaft bends the least. Take a felt pen and mark the bottom side of the of the shaft when it is in the spot of least difflection. That's the stiffest side. I place the stiffest side against the bow.

It's a simple and effective way to find the difference. The Sitks shows a lesser difference between stiff and weak side than do the heavier shafts; Alaskans, Safari and Big 5.

Hope that gets you up and running.

Ed
TGMM Family of the Bow

[Dr. Ed Ashby]

Peter,

The biggest problem has been the amount of modification required to get the single-bevels ready for final sharpening. Help, via broadhead and sharpening jig manufacturers, is on its way; for Tanto tip and all.

I have not yet tested any of the recent-to-appear single-bevels, but there are a lot of very complex force dynamics involved in getting the best performance out of a single-bevel BH. I'm not sure all the manufacturers have a grasp on that yet. I hope the rush to meet demands for more single-bevel BH's doesn't cause a flood of heads that do not perform as well as they should.

I'm hoping that there will be a selection of single-bevel choices available by fall.

Ed
TGMM Family of the Bow

[Ray_G]

Thank you Dr. Ashby.  I will ask a few folks I know if any have a spine checker.  The po'boy checker is certainly doable for the immediate time.

Ray

[peter c iacavazzi]

Thanks Dr. Ashby! I did speak with Ron at KME sharpeners and I know he is working hard at trying to help guys like me come up with a sharpening system.

I hope to be packing a quiver full of extreme FOC arrows all tipped with a razor sharp single bevel heads this fall!

Respectfully, Peter

[Missouri CK]

Dr. Ashby,

Thanks for taking the time to answer these questions.  

All the evidence and research sounds great to me, and I find myself thinking about ways I can incorporate it into my set up.  The problem I see is that it is going to become difficulty to practically apply some of the recommendations.  

For an example with some of the extreme FOC set ups its going to be tough to get a field point to practice with that is the same weight as the broadhead/adapter weight.

My set up sounds tame comparatively, but with my 65-70g steel adapter (which now seems flawed), my 140 grain STOS, and the 100 grain brass insert.  I already was at or near the max size of field points.  It just doesn't seem like a good idea to practice with a different weight field point.  If I go up to the 100 grain steel adapters to get away from the flaw in the smaller size I have basically gone beyond the size of most field points that I see for sale.

Any thoughts or suggestions on this matter would be appreciated.

Chris

[KSdan]

Chris-that doesn't seem like a problem.  100 gr brass insert + 100 adaptor + 125 head.  That is only 15 gr different than your current set-up.  And I would guess you could easily grind down the brass insert or modigy the field pt. that 15 gr if you really wanted.

Am I missing it??  Seems like this would work.  I need to do the same thing.

2c
Dan

[KSdan]

Chris- I did mean a 125 field pt.