Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on December 15, 2019, 01:13:25 pm
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With Perry Reflex there is something going on because of the tension/strain between the two pieces of wood. It stands to reason that the more tension the better. I remember reading that the thicker/stiffer the belly the better the final result. Does it also stand to reason that if you deflex the belly with steam or heat you will get better results from the Perry reflex?
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im over simplifying,, it would enable a bow to hold more reflex ,,,not sure about the deflex in belly,,
seems if both pieces were reflexed ,, it would hold more reflex,, I am just guessing,,
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Are you saying deflex the whole core then glue up into reflex or just heat deflexing the deflexed part of the D/R ?
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Deflex the whole core and then glue into reflex.
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Ok that's what I thought my guess is it would be counter productive , isn't Perry reflex just reflex held in by a glue line ? Of course there is only one way to find out >:D But the interesting thought would be to heat bend your core to your D/R profile I would bet you would hold the profile more then not doing it , in multi lam core that happens naturally to take the shape just my thoughts for what it's worth !
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I believe yes, as you are not compressing the belly until it reaches what would have been the relaxed position. That is my understanding. Some of the lam bow guys I know poo poo the whole thing...or much of it I should say. Seems to me to to be a reasonable conclusion.
I would be very curious what the results would be thru the chrono, one way vs the other to compare.
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I've already done one limb so it's gonna happen. I don't know that there will be a big enough difference to notice. I think there is more to Perry Reflex than just holding in reflex better although it definitely does that. I think there is some witchcraft involved ;) If you reflex both pieces and glue them together with no Perry they will just stay like that. The neat thing about Perry is that when you start tillering the bow will gain reflex. I think the reason for that is that when you release it from the glue up the two pieces are fighting each other and as you tiller you are weakening the belly so the back starts to win the equilibrium war so you get more reflex. I've had a bow gain an inch and a half in the first 10-15" of tillering. They seem to lose it all by the end of tillering. In my case because I'm tearing apart a "finished" bow and gluing it back together I won't be doing much tillering(touch wood). I'm totally willing to be convinced T'm wrong here as I don't have a good understanding of what Perry does. It does seem to work though, as my best bows are Perried. Could be coincidence though. To my way of thinking the idea is to create as much "tension" as possible between the two as possible and the way to do that would be to reflex the back and deflex the belly.
I guess I'm kind of thinking that if the belly's "normal" position is bent that it won't actually come under compression until it gets back to that postion. By then you're at half draw. Dunno, just a thought.
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Well at least your making the bow you can take me out of my arm chair speculation mode :OK
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I was treating the other limb and had time to think. Dangerous ;D If "if the belly's "normal" position is bent that it won't actually come under compression until it gets back to that postion" is true then it should be better if the back is deflexed before the glue up too then the back wouldn't be under tension til half draw. This is seeming silly. Anyway I've always thought that Perry Reflex must be temporary. Think about it. If there are internal stresses set up in the bow eventually the wood will readjust to accommodate them. If you leave a bow strung for a year it will have a serious bend to it. I think the same will happen to a Perry bow. After a length of time it will "set" into the new shape. As I was writing that I realised that I've split a bone dry stave and had one side bend one way and one bend the other so i guess some stresses will stay. Still puzzled.
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I have made 2 with perry reflex. Both broke on me and both at 27 inches. My fault on one and no idea on the other. Both were nearly done. Tension failure on both. So I have played with it some. I. Want to do another at some point.
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I think the stress is in the glue line. The problem I see is taking wood off the belly to tiller. That screws it up. The tiller needs to be close before glue up I think.
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I think slim is right on the glue line I have herd guys say that multi lam bows hold the reflex better but then you have the extra mass of the glue , but I would think a multi thinner lam core would handle stresses better but the bottom line is how it equates to performance , I think slim is also right on being close to proper tapper at glue up makes a difference the last bamboo bow I made I pre tapered the core & probably took 10 minutes to tiller keeped a fair amount of reflex but I think the closer you are to proper taper at tiller the more reflex your keeping with self bows to !
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I The problem I see is taking wood off the belly to tiller. That screws it up.
Why would taking wood off the belly screw it up?
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I have found that reflexing the core before glue-up is much better.
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I have a lot of interest in this subject, and to date no successes, so keep that in mind as I ramble through this, but giving the bow PR causes more stress internally so less stress on the surfaces. You want the back pulling against the belly at a stalemate. As you remove wood from the belly, and reflex increases, you lose the internal conflict because you weaken the belly. Now the PR advantage is lost and you end up with just a reflexes bow. I believe you want a thick belly lam and a thin back with both being well tillered before glue up. Side tiller to touch it up.
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Here's link to the explanation of Perry Reflex by Dan Perry. I still have to read it more carefully but I did see that the belly has to be full thickness. I'm not sure exactly what "full thickness" means. I took off the "H" You have to scroll down a bit to find Dan's post.
ttp://leatherwall.bowsite.com/tf/lw/thread2.cfm?forum=23&threadid=188683&category=
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I think his point on full thickness just stresses the point that thin lams won’t produce the same results as a “full” thickness belly.
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Interesting that Baker says the belly should be mostly reduced before glue-up and claimed Perry did this but Perry himself seems to indicate forcing a too thick belly into reflex is the way to go.
I do think that both their explanations for Perry reflex are speculative at best but both get to throw their weight into their statement due to them being considered guru's.
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I do think that both their explanations for Perry reflex are speculative at best but both get to throw their weight into their statement due to them being considered guru's.
Ain't that the truth but then that's the truth for just about everything in this world.
The one thing I know from personal experience is that you get more of that reflex gain while tillering if you use a thicker belly piece. Whether or not it has any influence on the outcome I have no clue. When you make a bunch of bows and they all come within 10fps of each other it's really hard to point a finger at what made one the best. Drives me nuts ;D, but then that's not a drive, that's a short walk. Pu dum dum ;D
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Don are you saying you end up with more reflex in the end after complete tiller using the thicker core or starting reflex ?
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I just taper the belly well before glue up and have had no issues...gut
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Don are you saying you end up with more reflex in the end after complete tiller using the thicker core or starting reflex ?
I've never done it because I think the set from my poor tillering hides it but yes it seems that way. You take it off the caul after glue up, measure the reflex and start tillering. As you tiller, keep measuring the reflex and you will find that it's increasing. Sometimes quite a bit. I guess if you could do a no set tiller it would keep increasing but I've never managed. l always wind up with some set. I lose the increase and usually more on top of that. Maybe something else happens I dunno ;D
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Im just saying to me it seems like all wood bows the more reflex you can start with the better off you are as far as retained reflex so it would seem to me the multi thinner lam could be reflexed farther to start unless heat treated reflexing the core like Marc said but I know with my current self bow I started with 5 1/4 reflexed and probably half that or better at 27" tiller so far so the same principal with less of a degree should apply to Perry flexed bows , like I said I dont no nothing but just thinking out loud !
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If I'm understanding this at all I think the sign is the increasing reflex. If you don't get any increase in reflex when you start tillering(it may not last :)) then you didn't get any Perry into it to start with. The whole thing keys around trapping the compressed back of the core(for lack of a better word) by gluing on the backing while the core is compressed. When the glue cures and you release it the core will try to straighten out. It will straighten until the tension of the back stops it. The two pieces are now in equilibrium. When you start to tiller you are weakening the core(belly). The tension of the back is now stronger and the reflex increases. If it doesn't increase then there was no tension between the two parts and therefor no Perry reflex. Talk me out of it if you can ;D ;D
PS All that said I still don't understand what those trapped tensions do to enhance performance. I don't think it's just increased reflex.
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Oh ok but it would seem to me the bow that would hold the most end reflex at the same mass would win the race , (arm chair theory) but what about Marc saying reflexed core works better for him ?
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There is a limit to how much reflex you can put into a bow. It would be nice to know if you had two bows, both with maximum practical reflex. One Perry and one steamed in. Would the Perry be better?
I know Marc has said he reflexes his bows before glue up. I very much respect Marc and his work. It's one of the reasons I question the whole thing.
My own experience seem to indicate that Perry reflex works but it's a limited sample and I could have just hit something else right.
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http://leatherwall.bowsite.com/TF/lw/thread2.cfm?forum=23&threadid=188683&category=
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I've had that open for a couple of days. I have read it before. I think that's where I got most of my knowledge about it. Time to read it again I think :D
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So far as I understand it...most of the tension and compression work is taking place on the surface of the back and belly under normal (non Perry reflex bows) conditions. PR causes some of that work to shift closer to the neutral plane (the glue line). That work is being added to the work the surface wood is doing. That is where the extra kick comes from. So far as I can figure.
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I just find it hard to grasp how something that is happening at the neutral zone has any effect at the surface. It would seem to me that any internal tensions would cancel each other.
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I think the bow with the perry reflex would have less mass ,, and give it an advantage over a bow with just steamed in relfex,,
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With my admittedly limited experience with this, something was certainly taking place. Both bows were heavier than expected draw weight. I read that it increases the stored energy by 10%. Some of that should translate to arrow speed. If it’s only 5% then 285 pushes to near 300. I don’t own a chronograph. I am wanting to know if you can document any improvement.
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I just find it hard to grasp how something that is happening at the neutral zone has any effect at the surface. It would seem to me that any internal tensions would cancel each other.
the wood is still working in shear closer to the middle, so it might help. slimbobs experience with breaking backs would seem to indicate something like boo would be a good choice, although I think Steves observation that "strong backing can mask a lot of set" (in the original post) would dictate a belly wood with superior compression qualities also.
Maybe yew for a belly? but designing/tillering so that the belly does not even come close to actually developing an apparent set?
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Steamed in reflex doesn't really seem to hold.
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"strong backing can mask a lot of set"
Sometimes I would settle for "masking" ;D ;D ;D ;D
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Steamed in reflex doesn't really seem to hold.
Yeah, steam is handy for getting the wood into position though. I have tried a few times to reflex a bow with just dry heat and had very little success. Use steam to get it to where you want and then heat it.
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Ok sorry I didn't mean steam :)
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Dry-heat including heat-treating when reflexing before glue-up will produce much better results
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I just find it hard to grasp how something that is happening at the neutral zone has any effect at the surface. It would seem to me that any internal tensions would cancel each other.
Clarence Hickman went into a detailed explanation of how this can be used in a bow in a mid-1930’s article on pages 55-59 of Archery, The Technical Side. Those pages are not the easiest read, but it is quite accurate. It even gets into how much benefit is possible and how to maximize it. Of course it wasn’t called Perry Reflex back in the 1930’s. It was known as “pre-stressing”, and has been used as a way to maximize strength of a composite beam or structure when loaded in one particular direction.
Alan
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Heat treating reflexing the core makes the most sense out every thing I have herd here because I still believe The bow that holds its profile (most reflex) is going to be a good performer & with the heat treated core making the belly denser & stressing the back the most with out breaking makes the most of the material used, its just comon sense over the magic of PR to me , Im not one to shun theory but I will take hands on exsperience by respected bowyers over theory any day !
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I just find it hard to grasp how something that is happening at the neutral zone has any effect at the surface. It would seem to me that any internal tensions would cancel each other.
Clarence Hickman went into a detailed explanation of how this can be used in a bow in a mid-1930’s article on pages 55-59 of Archery, The Technical Side. Those pages are not the easiest read, but it is quite accurate. It even gets into how much benefit is possible and how to maximize it. Of course it wasn’t called Perry Reflex back in the 1930’s. It was known as “pre-stressing”, and has been used as a way to maximize strength of a composite beam or structure when loaded in one particular direction.
Alan
All my "primitive" mind can think of is the case of "pre-stressed" concrete beams. What is stressed in that case is the steel cable. It is using the tension strength of the cable inside. In "pre-stressed" bow limbs, it would be the glue/epoxy that is used to hold the strength. If we just glue the slats flat, we will be using just the normal stress on the glue. But if we use the glue to hold the slats in the reflexed shape, we will be using the stressed tension strength of the glue/epoxy. That would be like inserting a more tention-strong material inside the bow limb, just like the pre-streesed steel cable. Basically we are changing the composition of the bow limb in the process. Just a thought. But using different glues and causing failures in the glueline might be a useful experiment. Do we have a glue that has the less tension strength than the wood?
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All my "primitive" mind can think of is the case of "pre-stressed" concrete beams. What is stressed in that case is the steel cable. It is using the tension strength of the cable inside. In "pre-stressed" bow limbs, it would be the glue/epoxy that is used to hold the strength. If we just glue the slats flat, we will be using just the normal stress on the glue. But if we use the glue to hold the slats in the reflexed shape, we will be using the stressed tension strength of the glue/epoxy. That would be like inserting a more tention-strong material inside the bow limb, just like the pre-streesed steel cable. Basically we are changing the composition of the bow limb in the process. Just a thought. But using different glues and causing failures in the glueline might be a useful experiment. Do we have a glue that has the less tension strength than the wood?
The glue line is holding a shear force between the laminates, but this force is distributed over the entire surface area of contact between the laminates. Most glues should be more than able to hold this without issue, unless the glue bond is very marginal to begin with.
In Hickman’s article, he glued up two straight laminates into a high degree of reflex to make each bow limb, and then he mounted these limbs on a handle that held the limbs in a large degree of deflex so the tips were not so far forward of the bow handle. By doing this, bracing the bow actually relieved the glued-in stress on the bow limb laminates. The result is a wood bow that can be kept strung all the time, and drawn further than a conventional design would normally allow. It was a pretty clever design.
I did some experiments with this a number of years ago. By varying the ratio of thickness of the two laminates, you can play all sorts of games. For example, you can offset excess tensile strength of a tensile-strong wood to provide relief on the compression side.
Alan
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By varying the ratio of thickness of the two laminates, you can play all sorts of games. For example, you can offset excess tensile strength of a tensile-strong wood to provide relief on the compression side.
If I recall correctly. Dan (in a follow up post maybe at PP, mentioned good results with 1/3 back lam : 2/3 belly lam.
that might have been for a hickory backed hickory though