Primitive Archer
Main Discussion Area => Bows => Topic started by: Don W on May 12, 2021, 01:25:45 pm
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I need some "mass principle" help before i drive myself further into the ibis of insanity than I already wander.
A little background: I have about 10 self bows I've made in the past year and a half or so between 45 and 65 pounds I shoot regularly. But recently I made the mistake of buying a chronograph. All of the bows I've made chronograph right around 130fps. I've tried multiple arrows weights but the typical 10gpp is were I am at, but don't really see a substantial difference either.
So my curiosity went on a research bender and came to volume 4 of the bibles and "mass principle". Seems easy enough right. Just build the bow keeping the mass in mind.
My first attempt (elm)is now down to about 45#. Its 70 inches ntn and well under 1 1/2 wide, tillered decent, shots ok, it is 28 ozs and shooting 113fps. Getting it down to 14.5 ozes would leave me with kindling.
My second attempt (also elm) is my cry for help. It's still about 50# at 20" draw or so. It's 1 3/4" off the fades about half way and tapers to 1/2" at the tips, it's 3/4" thick off the fades and tapers to a 1/2" thick at the tips.
Moisture content is just under 12% and both bends through the handle.
The second bow is just over 27 ozs and according to chart on page 92 of V-4 it should be about 14.5ozs. Now I know there is no way I'm going to loose almost 1/2 the mass of that bow and still have something to shoot.
I'm not doubting the principle, but my interpretation of it seems to be highly suspect, or I am totally missing something my head hasn't wrapped around yet.
Edit to add, My question wasn't so much about speed but weight. I understand my bows are overbuilt, the weight tells me that assuming the chart is correct, and I have to assume it is. I guess to simplify my question, or get back to basics, am I reading the chart right? Could a bow built like this really get down to 14.5 ozs?
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You have fades on a bend through the handle bow :o
More dimensions would be appreciated, like the front profile, string follow, and length of the handle.
12 seems to be the damper end for elm.
What kind of string do you have?
No offence, but I considered my first to be 'decently tillered' to.
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hopefully this is readable. Top number is width, bottom current thickness.
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Could be a number of things but based on your stats the moisture content is definitely high. 7-9% seems to be a good sweet spot for me. Your bows also sound overbuilt. For a bend through the handle bow of that length made of elm it could be quite a bit narrower. It’s possible your tiller doesn’t correspond to the profile or design. Photos and stats would be helpful. Also consider that the shooter is a huge factor for measuring speed. If you hold at full draw before releasing the arrow or short draw or don’t get a clean release, those can all result in lower speeds.
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maybe a little of all of the above things that have been pointed out, but can you confirm your drawlength when you are shooting thru the chrono? maybe have someone mark an arrow with a sharpie just before you release? have them make the mark at the back of the bow.
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My question wasn't so much about speed but weight. I understand my bows are overbuilt, the weight tells me that If the chart is correct, and I have to assume it is.
If all my bows are shooting the same, I'm obviously doing something wrong consistently, but let's not think arrow speed but bow weight. It doesn't seem logical to me that I could get that bow down to 1/2 it's current mass and still be at 50# or even close.
I know most of the bows I've built were around 9% mc. The second floor of my shop keeps everything about 8-9%. These particular now were not stored there.
I guess to simplify my question, or get back to basics, am I reading the chart right? Could a bow built like this really get down to 14.5 ozs?
Jim Hann wrote in his book an elm now 67", 2" wide would be 45#. Are we saying this wouldn't be following the mass principle and wouldn't shot 140fps?
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maybe a little of all of the above things that have been pointed out, but can you confirm your drawlength when you are shooting thru the chrono? maybe have someone mark an arrow with a sharpie just before you release? have them make the mark at the back of the bow.
I make my own arrows. My hunting arrows are 33" long. I've played around with a lot of different lengths and weights just playing around. If anything, I draw a tad over 28".
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In TBB Vol 1 I think they say a 66” bow that’s 2” wide to mid limb and tapering to the tips will pull a draw weight about the same as the woods‘a specific gravity. I have no doubt that bows can be built to those reported weights but, if my understanding is correct, Steve has since reported that he is getting higher numbers for mass depending on the design with equal or better performance due to lower set/hysteresis.
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maybe a little of all of the above things that have been pointed out, but can you confirm your drawlength when you are shooting thru the chrono? maybe have someone mark an arrow with a sharpie just before you release? have them make the mark at the back of the bow.
I make my own arrows. My hunting arrows are 33" long. I've played around with a lot of different lengths and weights just playing around. If anything, I draw a tad over 28".
I was asking if your form might be compromised when you are shooting thru the chrono. if you are short drawing during the testing, low readings might suggest erronous assumptions about all your bows
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In TBB Vol 1 I think they say a 66” bow that’s 2” wide to mid limb and tapering to the tips will pull a draw weight about the same as the woods‘a specific gravity. I have no doubt that bows can be built to those reported weights but, if my understanding is correct, Steve has since reported that he is getting higher numbers for mass depending on the design with equal or better performance due to lower set/hysteresis.
I've got that written in my notes. That doesn't mention the weight of the bow or the speed of the arrow. I can't seem to find anything that correlates all that information together in a single flat bow design/build.
I've read a couple threads (like this one http://www.primitivearcher.com/smf/index.php/topic,17218.0.html)
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The moisture and length is making it heavy. Don’t worry about it not weighing more than the Bible says. It’s where the mass is in the bow that robs speed. Keep the tips and outer limbs light. Green wood is down doggy. Arvin
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Looking at your original question, I think you’d need to start narrower and thicker to get that low mass. It’s not as if you could remove mass from your finished bows and maintain draw weight. It’s that your current bows aren’t built optimally including having the lowest mass cross section possible to get there without taking much set.
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sometimes if the bow is too long,, you have to cut it shorter and re tiller to get the mass down,,and keep the weight up,,
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130 FPS is not that bad. I am so terrible at shooting through the chrono by hands as to shoot about 20 FPS slower than using my crude homemade shooting machine.
Your bows are almost twice as heavy as expected. And you say they still shoot 130 fps. That's probably not impossible but rather suspicious. First, you need to check your scale.
Second, you need to check your humidity meter. Your bows might be even wetter than you think.
Third, you must be building your bows way too wider than necessary for the wood and design used.
You can put your bows in a heat box, or even heat treat them. You can also narrow them and spike them if necessary to keep the draw weight. Good luck.
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What is your full draw length? If you have a short draw length you can't expect to have stellar arrow speed from any bow, self or laminated.
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The length of the bow doens't matter one jot. You simply need to mtach the tiller profile to the bow design. Remeber the 80" pecan (?) bow is TTB. Same as all the elbs I make they are shocky if you get the tiller wrong. In a longer bow that generally means npot having enough bend mid to outer limb and or too much bend near the handle.
If I said to you do a pyramid bow and a parallel limb bow have the same tiller? Do you know what I mean? This is what Ryan mentioned above if the tiller shape doesn't match the limbs width taper you will never make an 'optimal' bow. Get the TBB 3 it explains 'tiller logic'. This principle alone will allow you to get closer to high performance more so than obsessing on the physical weight. The mass principle is something to apply AFTER you have tiller logic dialled. A well tillered bow with correct profiles will shoot much faster than the speeds you are getting.
Your moisture content is also high, elm is best around 8 -9%. Also think how heavy water is :)
Your long and wide elm bow will be way over physical weight by the sounds of it. A long bend through the handle elm bow should be 1 1/4" wide max through the center section with no fades.
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sometimes if the bow is too long,, you have to cut it shorter and re tiller to get the mass down,,and keep the weight up,,
YES!
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But there are references of bows of specific length at specific weights. Yes, cutting it down can keep draw weight up but the expected mass will also continue to go down for that design. I think Don is wondering how it’s possible that his bows are so much more massive than Steve’s mass principle results and if it’s even possible to make bows of those stats.
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I have made some progress and discoveries. I know a little more than I did. And that's the goal, right? First, I think I was not interpreting the chart correctly. If I compare it to the list in the next chapter of the bows tested (page 110), the numbers relate closer to the left hand column. I took my HHB bow and tried to recurve it. That broke the tip, so I had to shorten it 6". At that point I didn't have much to loose. Doing all work on the sides i managed to get a bow that is 6" shorter, 1pd lighter and 10fps faster at the same draw. That's with a boat load of mistakes along the way. I also took one of the oak board bows. Tore into it, narrowed it as I watched the weight, and speed. The speed obviously decreased, but at a slower rate than the weight. It's not done yet i ran out of time. After shortening it, it's now a 45# bow shooting 140fps with a 400gr arrow. Weight is in between the two numbers on the chart, but it's also got a longer handle and fades. That's so much better than it was. I think the moral of the story is don't take the chart quite so literally. Just let it be a guide.
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you making progress,, :)
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Yes one of my best pyramid bows came in at 28 oz. But most of the mass is in the handle and fades to mid limb. The he expected at mass demonstrations d not affect the speed that much. Overbuilt maybe but no ones beat it yet. So no the charts aren’t everything. Arvin
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The principle is maybe a bit outdated. Not long after it came out it was already being revised.
I don't bother weighing bows for mass. It doesn't seem like a number to chase.
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If it worked then it should work as well now. I think better systems could be had, but I don't think most of us would be able to appreciate the difference, much less incorporate it into our work.
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also I do believe if the bow is designed for a short draw, stellar arrow speed can be achieved,, the longer draw can give you an advantage, but the shorter draw can have great cast,,as well,, even with hunting weight arrows,, stellar being being open to interpretation :)
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The principle is maybe a bit outdated. Not long after it came out it was already being revised.
I don't bother weighing bows for mass. It doesn't seem like a number to chase.
That's fine if you already know how to build efficient bows. It's definitely a learning tool for us who need it
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If I have a bow thats shooting like a dog, I will check it to see if I have overbuilt it,, but if its shooting really well, I might check the mass weight just for fun,, its usually in the ball park,,
if you make a bow with tried and true design, it will probably shoot well, for example like 66 inches long 1 1/2 wide, ,27 28 draw,, it will shoot nice,,and probably be close on the chart,,
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The principle remains true qualitatively in that we want the lightest mass cross section without taking set and that mass distribution/movement allows varying degrees of flexibility in terms of how much we have to push for low mass.
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The principle is maybe a bit outdated. Not long after it came out it was already being revised.
I don't bother weighing bows for mass. It doesn't seem like a number to chase.
That's fine if you already know how to build efficient bows. It's definitely a learning tool for us who need it
It might make you jump too far to the extreme though. Steve builds bows in large quantities and tends to not shoot them for too long before moving on to the next one. He also wants them to remain brand new and fresh. That leaves no margin for error and may be why the pendulum has swung back to at least slightly overbuilt bows.
It's more of a learning tool for after you have considerable experience.
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The principle is maybe a bit outdated. Not long after it came out it was already being revised.
I don't bother weighing bows for mass. It doesn't seem like a number to chase.
That's fine if you already know how to build efficient bows. It's definitely a learning tool for us who need it
It might make you jump too far to the extreme though. Steve builds bows in large quantities and tends to not shoot them for too long before moving on to the next one. He also wants them to remain brand new and fresh. That leaves no margin for error and may be why the pendulum has swung back to at least slightly overbuilt bows.
It's more of a learning tool for after you have considerable experience.
It sounds like you don't think it's the best avenue to pursue. With 10-12 bows under my belt that shoot ok and a desire to get better performance, what would be your recommendation? After all that's the ultimate goal here is just continue to get better.
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Speed matters. You need to shoot for around 100 plus your bow's draw weight in FPS using a 500 grain arrow. That's not easy for beginners. Once there, it's up to you what you want from your bows. You can go after appearance, style, efficiency, world records, or whatever that matters to you. For me, physical exercise itself in making bows, without making too much dust, is what matters most, because of my sedentary lifestyle. Still I consider a bow a failure if it does not have enough speed in it. Good luck.
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Don, I’d recommend making sure your tiller is spot on. If you can make bows with low set and good string tension at brace then speed will follow. Keep those tips narrow. No need to be wider than 3/8” at the tips. Avoid inner limb set.
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The principle is maybe a bit outdated. Not long after it came out it was already being revised.
I don't bother weighing bows for mass. It doesn't seem like a number to chase.
That's fine if you already know how to build efficient bows. It's definitely a learning tool for us who need it
It might make you jump too far to the extreme though. Steve builds bows in large quantities and tends to not shoot them for too long before moving on to the next one. He also wants them to remain brand new and fresh. That leaves no margin for error and may be why the pendulum has swung back to at least slightly overbuilt bows.
It's more of a learning tool for after you have considerable experience.
It sounds like you don't think it's the best avenue to pursue. With 10-12 bows under my belt that shoot ok and a desire to get better performance, what would be your recommendation? After all that's the ultimate goal here is just continue to get better.
Keep striving to improve your tiller and minimize tip weight. Reduce limb width as that gets better, shorten the bows relative to draw length or make the working limb shorter....
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The original purpose of the mass theory was to be able to produce good performing bows that did not take too much set. The goal was never to minimize mass. On the contrary it leaned heavily toward making sure we had enough wood to not take excessive set. For example, my typical osage bow 50# and 64" long stiff handles would usually come in around 16 oz. Using the mass principle they now come in between 19 and 20 oz. Over the years I have found several things in the mass theory that tend to discredit it on some applications while for the most part I find it usually works quite well for me.
A few years ago I built a number of backed English long bows, some of them were backed with hickory or other white woods while others were backed with bamboo. The lengths ranged from 67" to 72". The belly woods were primarily ipe, cherry, bullet wood, maple, white oak and red oak. With the exception of the red oak which lagged slightly behind the others but still performed well they all shot around the same distance and some of them broke world records in the English longbow classes. What was interesting was they all came out at the same mass weight but the physical dimensions were vastly different. When finished they all adhered pretty closely to the 5/8 rule of thickness to width. What didn't make sense to me was how thick the cherry bow came out when finished.
Another one I have no answer for is how light deflexed reflexed recurve bows come out, far below projected mass. ( Mark St Louis style) Especially on the shorter versions ( 60" and below).
And the big one that throws a screw into the whole mess was when I decided to go super wide on some osage bows just to see how they would perform. I was expecting a significant gain in mass weight however they actually came out lower in mass inspite of the extra width. The only logical explanation I can come up with for that is that we may be doing more damage to the wood than we think we are even when it doesn't show up in set.
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cool :)
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So how well did the supper wide bow preform? What were the dimensions? Did it have narrow outer limbs?
Sorry for all the questions, sort of :D
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I don't remember now if I chronoed the bow but I did take it out and shoot it for distance and it performed well. I ended up recurving it with big recurves several inches behind the back. I know it ended up taking set after that. I think it was about 2 1/2 inches wide maybe a bit less. The bow had a short working limb area and the tips were stiff and narrow.
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well, if anything this has help me understand I still don't understand. But I am definitely going to pay attention to mass and i'll try that "no set tillering" process. I've made a couple bows shot better and are definitely lighter now, but i never was one to shot for average. And I'm way to old to think I have time to do something like build 25 pyramids of all different lengths, about 25 elbs of all different lengths and about 25 parallel limb bows all different lengths. But i guess I can die trying!
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The easiest way to do "no set tillering" is to build two identical bows with same "no character" material and never bending one bow while working on both of them at the same time. The finished bow that has never been bent will have no set, at least until you start bending it too much.
There are several "perfect bow" designs available online. You can pick one and simply keep on making bows of that design until you "make" it.
Cf. Topic: Best bow design?
http://www.primitivearcher.com/smf/index.php?topic=9274.0
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Most of the bows I've built are American flatbows. Parallel limbs about half way looks best to me. I don't like the looks of a wide pyramid bow.
I'm sure i will have one of the "duh" moments at some point, but the theory behind the perfect tiller alludes me. I get that taking off the sides takes more mass than draw weight. But to narrow and wood will crystalize. So it's a tightrope walk between to narrow and to much mass.
I am also assuming there are a lot of game taken with bows that are not necessarily efficient. Speed is secondary to accuracy and weight? I'm sure there is a sliding scale somewhere to show that.
The baffling part is all the videos I've watched and all the texts I've read, it's always "take some wood off the belly" to get the right bend. Yes they mention keeping the tips narrow but never mention the rest of the limb.
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That's because most people fit tiller to front view shape so you only need to take wood off the belly to work on tiller. You could take wood off the sides if you thought you had too much mass but most folks already have starting dimensions in mind when they shape the bow
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That's because most people fit tiller to front view shape so you only need to take wood off the belly to work on tiller. You could take wood off the sides if you thought you had too much mass but most folks already have starting dimensions in mind when they shape the bow
So how do you know what your starting dimensions should be? If it were that simple it would seem someone could post the perfect dimensions and thickness and then you could just follow those dimensions every time for the perfect bow. But that doesn't work, right?
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Just had a pyramid I made a year or so ago. Osage 66", 13" non working handle 1/4" at tip and 1' 5/8ths at fade maybe 3/8th thick. Never shot it much and di not hunt it at all. Picked it up and start shooting it and noticed it gained some weight. Blowing arrows right over target. Limbs on this bow weigh nothing but riser weighs a bunch. Very shot working limb. Shoots wonderful.
Guess it depends what your doing with a bow? If your playing games I guess speed helps. If your feeding a family or two or three a selfbow that shoots well without holding it sideways and shoots a 550-600grn arra 125-135fps will kill everything you'll ever need to keep babies smiling.
Hedge~
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I don't necessarily call learning to make a better bow, "playing", although I do tend to latch onto something and want to learn enough to be good at it. I can make consistent 130fps bows.
I'm sure all the author's in tbb felt the same
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Games is games. Flight, 3d, field, 2d, IFAA, NFAA, WA, games is games. Just like NRA or CMP matches and are called Games Matches.
A selfbow, non backed you shoot over and over and over for years that'll do 135-155fps of any mass with a 500-550 or so grain arra is real quality tool /wpn. Building one of these is not to awful difficult using good wood put up right and tillered out slowly. Prolly not going to do it your first few bows but ya will shortly. Over tens of thousands of shots and years of poking the pucker brush I think it's hard to beat a good elm, take yer pick cept the red stuff.
HH~
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That's because most people fit tiller to front view shape so you only need to take wood off the belly to work on tiller. You could take wood off the sides if you thought you had too much mass but most folks already have starting dimensions in mind when they shape the bow
So how do you know what your starting dimensions should be? If it were that simple it would seem someone could post the perfect dimensions and thickness and then you could just follow those dimensions every time for the perfect bow. But that doesn't work, right?
I base my dimensions on experience based off of all of the bows I’ve ever made and trying to find dimension of bows others have made. I know based off of previous designs that if a wood is a certain density then I will need to make it a certain width based on the design/draw weight I want to make. The thickness is more determined by the working limb length and draw length as that doesn’t seem to vary much across hardwood species. I’m not so nit picky that I’m going for absolute perfection but I’ve been able to achieve low set (<1”) pretty consistently. A couple times where bows have not taken any set I started to remove wood from the sides later in the tillering process and those were with exceptional pieces of wood. Judging wood based on density can allow you to use new woods with higher success as the other properties of compression/tension strength are usually not a huge factor if making conservative flat bow designs with flat bellies.
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So how do you know what your starting dimensions should be? If it were that simple it would seem someone could post the perfect dimensions and thickness and then you could just follow those dimensions every time for the perfect bow. But that doesn't work, right?
In TBB Vol 1 I think they say a 66” bow that’s 2” wide to mid limb and tapering to the tips will pull a draw weight about the same as the woods‘a specific gravity.
A specific gravity test is easy, and other rules of thumb are mentioned in TBB. As I recall, different starting widths for different densities
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That's because most people fit tiller to front view shape so you only need to take wood off the belly to work on tiller. You could take wood off the sides if you thought you had too much mass but most folks already have starting dimensions in mind when they shape the bow
So how do you know what your starting dimensions should be? If it were that simple it would seem someone could post the perfect dimensions and thickness and then you could just follow those dimensions every time for the perfect bow. But that doesn't work, right?
I base my dimensions on experience based off of all of the bows I’ve ever made and trying to find dimension of bows others have made. I know based off of previous designs that if a wood is a certain density then I will need to make it a certain width based on the design/draw weight I want to make. The thickness is more determined by the working limb length and draw length as that doesn’t seem to vary much across hardwood species. I’m not so nit picky that I’m going for absolute perfection but I’ve been able to achieve low set (<1”) pretty consistently. A couple times where bows have not taken any set I started to remove wood from the sides later in the tillering process and those were with exceptional pieces of wood. Judging wood based on density can allow you to use new woods with higher success as the other properties of compression/tension strength are usually not a huge factor if making conservative flat bow designs with flat bellies.
Does this maintain the average or better arrow speeds?
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Great question. I’m not much of a shot, especially in front of a chronograph. But from the few I’ve tested they seem to be above the averages described in the bowyers bible. Now-a-days people are putting out awesome bows so I bet they’re pretty average overall.
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make it as complicated as you need,, but 66 inches 1 1/2 wide,, will make a nice shooting bow,,fast flight string, and it will out shoot average bows from 20 years ago,, just try it and see what you think,, stiff handle or bendy,,