Primitive Archer
Main Discussion Area => Bows => Topic started by: Selfbowman on March 03, 2023, 02:15:18 pm
-
Ok guys Alan was nice enough to give me a design to build by and I was fortunate to have a real clean. Flat Osage stave. The design was close to my caul I normally use. The growth rings I don’t consider ideal but good and even in thickness. So. We will see how this turns out and how good I am at following the engineers drawings.🤠🤠
-
Y’all have seen enough of my bow builds to get this up to speed. I’ve roughed the stave out and did my first heat bend and straightening.i have the back close to width. I am marking my thickness edge to desired thickness by Alan . I will get this close and reheat the limbs to the caul. I want to hit his profiles Ass close as Arvin can do.
-
This is my thickness marks on the edge.
-
Now to connect the dots and take off the excess.
-
Pic
-
After the most thickness has been removed we are back to the caul.
-
Third heat session.
-
Where is bowanarro? I know he will speak the truth.
-
Caul looks good. It’s hard to see the numbers though. From the pic it appears the heat treatment was fairly dark. It may just be the lighting.
-
Wow Arvin that’s a lot of numbers to keep up with 🤔 Pappy
-
Very interested in seeing the outcome. Will definitely be following along on this one.
-
Wow Arvin that’s a lot of numbers to keep up with 🤔 Pappy
Yes it is.i have a good stave so it’s going to be a lot of filing and 80 grit to hit all those numbers.🤠🤠
-
Arvin, looking good. That's pretty precise stuff. Jawge
-
Yes it is.i have a good stave so it’s going to be a lot of filing and 80 grit to hit all those numbers.🤠🤠
are you also going to tiller , or ship it undrawn?
-
I have never tried that, so I am guessing ,, you might have to adjust the tiller even if you hit the numbers,, :)
-
I am going to hit those measurements real real close . Put it on a long string check it to 20” draw. But I suspect if I hit the measurements right it will be spot on at full draw. If not me and the engineer will have a sit down talk! 🤠🤠🤠
-
I am going to hit those measurements real real close . Put it on a long string check it to 20” draw. But I suspect if I hit the measurements right it will be spot on at full draw. If not me and the engineer will have a sit down talk! 🤠🤠🤠
It’ll be interesting to see what the tiller looks like.
I would think if the numbers are right and both bows were made from clean wood, it should be pretty good.
Maybe a different in weight but a similar bend.
The numbers would have to be really good not to need a little fine tuning though.
(-P
Bjrogg
-
Oh so this is real test for the engineer and old Arvin is what you are saying BJ. Now that I am about to try to hit those numbers I’m beginning to wonder what i got myself into!🤠🤠🤠🤠
-
variations in the wood,, could effect what the numbers do,,since all wood and staves vary,, but you should be close,,
but I wouldnt really know till I got it to full draw and shot it a bit,, the wood may settle in various ways,,and it may need a bit of fine tuning before full draw is a good idea,,will be interesting to see how it goes, thanks for posting,, also moisture content will effect how the stave reacts to bending,,
do you know the mositure content of the bow you using the numbers from,,,
-
Ok guys Alan was nice enough to give me a design to build by and I was fortunate to have a real clean. Flat Osage stave. The design was close to my caul I normally use. The growth rings I don’t consider ideal but good and even in thickness. So. We will see how this turns out and how good I am at following the engineers drawings.🤠🤠
Very cool, Arvin. I look forward to seeing how it all works out. My limited experience with designing a bow and building to the design says it will be very close on the tiller and you will only have to fine tune the last few percentage points on the tree.
Mark
-
Brad the meter is blinking 6% . The owner’s manual said this would of be below 5.5%
-
well it seems a little dry for osage,,maybe get some input from others,, just me,, I would put somewhere not so dry and sprits it or something,,, the stave the bow was measured from might not have been that dry,,just guessing,,its hard in winter things get so dry,, maybe start a thread,, is my stave too dry and see the response
-
Well I got down to checking my numbers . Cut the knocks in. Put it on the tree and I pulled th long string to where the tips came almost to brace . Seen area that needed more off. Well that’s where the fine tuning needed to happen on my numbers. I think we missed our weight of fifty pound draw weight. Just the way it feels at floor tiller maybe 40-45
-
Now at fine tuning. I checked thickness at all spots of the limbs if off a hair I put one mark . If two hairs needed to come off I put 2 marks. You get the program. Ok smart guys laugh! Guys this is real good for tuning your finger calipers. I know there is bowyers on this site that have real good finger calipers.
-
Brad just stay tuned in. I’ve got some places that I need to add a hair.🤨🤠 this going to be a fun experiment. Engineer vs. Builder 🤠🤠
-
Brad just stay tuned in. I’ve got some places that I need to add a hair.🤨🤠 this going to be a fun experiment. Engineer vs. Builder 🤠🤠
This is interesting Arvin.
It definitely isn’t how I build a bow. I’m definitely not the building to measurements type.
I rarely measure anything more than the length and rough handle dimensions.
I often get asked for measurements. It seems like I work with so much character wood that doesn’t tend to follow the blueprints.
Be interesting to see if the really clean wood will
Bjrogg
-
BJ your one of those finger calipers guys I was thinking of!
-
BJ your one of those finger calipers guys I was thinking of!
Yes I am.
Honestly I shouldn’t say I never measure anything because I constantly measure them. Just can’t put a number on it
Bjrogg
-
It definitely isn’t how I build a bow. I’m definitely not the building to measurements type.
I often get asked for measurements.
Be interesting to see if the really clean wood will
BJ, there is nothing wrong with doing it by eye and finger calipers. If you know what you are doing then it will get you a very good bow in the end. Your measurements only work for the wood you have, anyway. For the next piece the modulus of elasticity and strain limits will be different and require different dimensions.
So far I have found that straight grain boards do follow the design numbers very well. Your character wood will also follow the same laws of physics but it doesn't look like it because you have to work around knots, bends and other features that affect how it appears in the end even if the actual width and thickness is to the math.
One thing I have found from using software to do the design is it gets the bend so close to perfect right from the start that my tillering eye has improved when I look at one that isn't bending correctly. This was an unexpected benefit.
Mark
-
I agree Mark.
The character ones do follow the rules but it’s more of a find the right average of the numbers and my fingers just seem to be able to compute them automatically. Even though I can’t tell anyone what they are.
Bjrogg
-
Even old related math Arvin is learning from them. Him and his hairs! 🤠🤠🤠
-
Where is that’ AVCase? Just like a Engineer . Never wants to come to the job site.🤠🤠🤗
-
Fine tuning the profile. Spent more time on the heat bench than I have sanding.
-
Bend coming soon.🤠
-
Now I’m getting interested.
If the numbers get those profiles I will definitely be impressed.
Those outer reflexes are working pretty good.
Bjrogg
-
Im still concerned about the low moisture content,, do you think its ok,,
-
Im still concerned about the low moisture content,, do you think its ok,,
Me too a little bit. Should find a swimming pool?🤠
-
That’s as close to the profile as I’m going to get for now.
-
Brad just stay tuned in. I’ve got some places that I need to add a hair.🤨🤠 this going to be a fun experiment. Engineer vs. Builder 🤠🤠
This is interesting Arvin.
It definitely isn’t how I build a bow. I’m definitely not the building to measurements type.
I rarely measure anything more than the length and rough handle dimensions.
I often get asked for measurements. It seems like I work with so much character wood that doesn’t tend to follow the blueprints.
Be interesting to see if the really clean wood will
Bjrogg
I build the same way you do BJ. I couldn't tell you the thickness of any bow I've ever made.
-
Brad just stay tuned in. I’ve got some places that I need to add a hair.🤨🤠 this going to be a fun experiment. Engineer vs. Builder 🤠🤠
This is interesting Arvin.
It definitely isn’t how I build a bow. I’m definitely not the building to measurements type.
I rarely measure anything more than the length and rough handle dimensions.
I often get asked for measurements. It seems like I work with so much character wood that doesn’t tend to follow the blueprints.
Be interesting to see if the really clean wood will
Bjrogg
I build the same way you do BJ. I couldn't tell you the thickness of any bow I've ever made.
[/quo
I did the t the same way till I got these plans. 🤠it could get back to that real soon.🤠🤠
-
Bend coming soon.🤠
Hey Arvin,
It looks like I didn’t send you all the pieces of the jigsaw puzzle! Hahaha!
-
Uh oh. Hopefully not to late to use the rest of the puzzle pieces?
-
Uh oh. Hopefully not to late to use the rest of the puzzle pieces?
I was just joking about the missing sheets in the photo that depict the side profile as the bow is drawn.
-
Alan do I need to correct those ends before I. Go farther?
-
I'm watching this with interest. How long and wide is the bow? Typical pyramid design?
-
Very cool experiment. I’d have to say the same as others here that the wood staves I have on hand wouldn’t allow for me to build a bow this way. Should be interesting to see how it goes. There seems to be a lot of inner bend on the outlined projected profile marked on the paper to my eye. Maybe it’s an illusion just being on the paper and will look better when actual bow is bending. I’m watching this.
-
Alan do I need to correct those ends before I. Go farther?
Yes, because you said you wanted that much reflex in the beginning. :) Otherwise, there won’t be much point in matching it up visually to the braced and full draw side profile shapes. It needs a little more about 13” from the tip.
Having said that, I have no idea how the heat bending affects the wood properties. But this is a lower stress area so it may not affect things very much.
One more thought. Reflex is a killer for wood bows, so less reflex like you show here makes it easier. It changes things. The limbs will need to be a little thicker.
Alan
-
so the numbers would need adjustment for the new profile,,?
just some thoughts,,
you wont know what your profile will be like till you string it and pull to target draw weight,,,, its gonna shift, if it was sinew backed it would hold closer, but self bow is a little trickier ,,
a fiberglass bow will hold,, but this is a wood stave,,
when it gets to full draw it will probably shift more,,
the long string is one thing, but braced is a different pressure on the bow,
you may have to re adjust the profile after you see what it does at full draw,, right now you are just guessing,,and all the heat treating is making it dangeriosly low in moisture content,, most of the bows I blew up,, and measured the moisture content right in the middle of the stave were low in moisture content,,
-
Alan do I need to correct those ends before I. Go farther?
Yes, because you said you wanted that much reflex in the beginning. :) Otherwise, there won’t be much point in matching it up visually to the braced and full draw side profile shapes. It needs a little more about 13” from the tip.
Having said that, I have no idea how the heat bending affects the wood properties. But this is a lower stress area so it may not affect things very much.
One more thought. Reflex is a killer for wood bows, so less reflex like you show here makes it easier. It changes things. The limbs will need to be a little thicker.
Alan
Arvin, I checked the impact of having the tips reflexed 2” like you have Vs. 2-3/4”, and the difference turns out to be very small. There is almost no impact to the braced shape and full draw shape. Bending stresses go down by 3% and you lose a little bit of stored energy. The limb needs about .007” increase in thickness to hit the same draw weight. No cutting corners! Hahaha!
-
what effect will difference in moisture content have,,? its a big piece of the puzzle,,
-
you may have to re adjust the profile after you see what it does at full draw,, right now you are just guessing
Which profile are you talking about here? The point of Alan's work is to not be guessing. If Arvin gets the thickness and width accurate to Alan's numbers then the tiller will not be a guess, it will be very close to what was predicted (assuming the wood properties are consistent along the length of the bow, which is a reasonable assumption). It is relatively easy to calculate the width and thickness to give you the tiller you want, the big questions are what the draw weight will be and how much set it gets because those are determined by the modulus of elasticity and the strain limit of the particular piece of wood and they all vary a bit.
The thickness numbers need to change with the reduced reflex because it changes how much strain the limbs see, which changes the draw weight.
For those saying they couldn't do this with a stave, this method does take very clean, straight grained wood because you are using rectangular limb sections and can't chase a ring on the back. I've done it with boards and lams cut from boards. The lams work the best in terms of being able to pick the best grain for the back and for the ease of achieving the desired thickness and taper rate.
Just to show that Alan and Arvin are not guessing, here is a red oak lam bow I designed using some of the same software Alan uses. I glued it up, cut the width profile and exercised it out to full draw on the tree with no tillering done (which is a good thing, because I'm still a hack at tillering by eye). The bend was not a matter of luck or guessing, it is the result of using math to predict the behaviour of limbs as structural members. These are essentially the same calculations used to design buildings, bridges and other structures, just applied to bows instead.
(https://i.imgur.com/dFHOxfr.jpg)
(https://i.imgur.com/s6xqU03.jpg)
Mark
-
the red oak lam bow is not the same as an osage stave,,
so dont think that is a good comparison,,
you wont know what kind of set the bow is going to take until you shoot it,, at given draw,,
you dont know what the profile will look like till you shoot the bow,, because its gonna change,,it may not change much,, but it will change,,and when the bow goes to a more humid place,, and has a reasonble moisture content it will take more set,, and unstrung profile will be different again,,as well as the tiller,,
its not a straight grain lam bow,, clearly,
if the limbs are out of tiller you will have to adjust it,,it wont matter what the numbers say,,,or how closly you measused,, if the wood shifts,, which it usually does,, depending on the finger pressure of the shooter,,,drawing the bow on a tree has a different effect than somone actually shooting the bow,,
I think the bow will be very close,, im just saying it will probably have to be adjusted after it is shot in,,or the moisture content changes,,
math connot predict what the bow wood will do under the strain of full draw,,,if the shooter has a longer hold,,, the wood may take more set,, or if the bow is left strung all day during hunting it will effect the tiller and set the bow takes,, if the bow is over draw at some time,, it may take more set,, one limb may take more set than the other after shooting,, these are not predictable,, the math is a great start,,
the red oak bow looks great,,,how many times had the bow been shot when photos were taken,,
-
Arvin, is it 5% on the surface or all throughout? I keep checking as I build. Jawge
-
math connot predict what the bow wood will do under the strain of full draw,,,if the shooter has a longer hold,,, the wood may take more set,, or if the bow is left strung all day during hunting it will effect the tiller and set the bow takes,, if the bow is over draw at some time,, it may take more set,, one limb may take more set than the other after shooting,, these are not predictable,, the math is a great start,,
The reason I am very interested in this study is that it provides an opportunity to learn more about the variables and changes in the materials that occur when building a real bow from a stave. For example, differences in the model compared to the real bow may give an indication to how much non-visible set occurs and how much effect it has. In this case, the bending stresses should exceed what I have measured in osage test samples that I have tested, but Arvin routinely achieves this with other bows he has built so I just ran with it.
Alan
-
Jawge I think all throughout. It’s 4-5 years old. Up date . The bow came out at 35@28. Well I’ll say!🤠🤠 I think this is combination of several things . The bow weighs 20 oz. That’s s less than my normal 50# 67” bows by a couple oz. so this wood is not as dense. The engineer may been using a different wood model. And Arvin was close but not spot on . The back of was as flat as a glass bow. No knots. It had more early ring than I liked. It took 1” set pretty much throughout the limb. So that tell me that Alan and I did our work pretty good but we over estimated the wood. Fun experiment and I will continue the try a few more. I think the next one I will try to duplicate my wide pyramid in a real rectangular limb design and see how it comes out. If great then I will have pieces of the stave to send Alan with measurements and do this experiment in reverse . Having the computer check Arvin.🤠🤠🤠
-
It’s sure fun to back at it!
-
Hey Arvin, how wide and long is that bow?
-
thank you for posting,, very nice ,, :)
-
Nice bows and very interesting cooperation Arvin and Avacase! A rectangular cross section might be the most efficient, as long as it matches the specific wood used. Curious about you being reverse checked Arvin :)
cheers
-
the red oak lam bow is not the same as an osage stave,,
so dont think that is a good comparison,,
I would say that wood is wood as long as you know the properties of the individual piece. As long as it is consistent along the length of the bow (which isn't always the case) it will always bend as predicted.
you wont know what kind of set the bow is going to take until you shoot it,, at given draw,,
Yes. As I said, the two things that are hard to predict really accurately are draw weight and set, because they depend on properties of each individual piece of wood. As long as the wood in the bow is consistent from end to end then I can predict the bend pretty accurately. If you have a knot or soft spot then it will throw that off.
drawing the bow on a tree has a different effect than somone actually shooting the bow
Yes it sure does, even if you set the bow to rock on the tree and pull exactly where the archer will.
I think the bow will be very close,, im just saying it will probably have to be adjusted after it is shot in,,or the moisture content changes,,
This sounds about right. I figure the math will get you over 95% of the way home, but wood always has a few quirks that may require attention.
the red oak bow looks great,,,how many times had the bow been shot when photos were taken,,
It was finished in the one picture, so it would have been shot hundreds of times by that point.
The engineer may been using a different wood model.
To be 30% off in draw weight means the modulus of elasticity was a fair bit different than what Alan assumed it was. This is one of the challenges of doing this with wood. If I want a bow to be spot on for weight I will do a bend test sample off that specific piece of wood in order to be as close as possible. Limb thickness also plays a major role, but you would have to be off a fair amount to lose that much weight. If you were careful with removing material and measuring with calipers you should have been close enough to be in the ballpark.
A rectangular cross section might be the most efficient, as long as it matches the specific wood used.
Rectangular is absolutely the best cross section in terms of sharing the strain equally among all the wood in the limbs, but that isn't always the only consideration involved.
Mark
-
when you glue lams together,, it is very different than a self bow,, perry reflex is a good example,, the glue enables the bow to hold a reflex a self bow would not,, and if the backing is too thick it will crush the bow,, the glue lines and lams are different than a self bow, even though wood is wood,, the glue changes that,,
its seems to me if you pull a bow on a pully there is one pressure point on the string,, if you shoot the bow then there are usually three fingers on the string,,, that makes the pressure different on the limbs,,, and the tiller may need to be adjusted for that,, I think thats why when the bottom limb is a bit stiffer it compensates for that and makes good arrow flight easier to achieve,, if the shooter does not have a good release,,,the tiller wont make much difference,, but as the shooter becomes more proficient,, the difference is more clear,, especially on shorter bows,,,
-
Hey Arvin, how wide and long is that bow?
[/quote
1-1/2 to mid limb or there abouts. 67” ntn
-
the glue lines and lams are different than a self bow, even though wood is wood,, the glue changes that,,
I keep seeing people say this, but no one has ever convinced me this is correct. Glue lines are very thin and the glue should be as strong and stiff as the wood if the bow is to survive, so why would it change how a limb bends? I agree using lams allows techniques that aren't available with a solid piece of wood, but if you cut strips off a board and then laminate them back together why do you think the properties have changed?
its seems to me if you pull a bow on a pully there is one pressure point on the string,, if you shoot the bow then there are usually three fingers on the string,,, that makes the pressure different on the limbs,,,
I agree. How a particular archer applies finger pressure can affect the tiller a bit and a bad release really does screw everything up.
Mark
-
The difference between a 50# design and 35# real bow is too great to easily explain away with a typical amount of variation in material properties.
Difference #1: Engineer used wrong material properties (-6 pounds draw weight)
I went back through my tests of various osage material samples, and compared those material properties to the material properties I actually used. Guess what I found? The engineer (me) was not using the same properties in my model as I had measured! This explains a little under 6 pounds draw weight difference.
Difference #2: The real bow had about 2” reflex instead of 2.75” in the design. (-2 pounds draw weight)
This explains about half the discrepancy. I would have expected the real bow to be around 42# at 28” after correcting for these discrepancies.
So, where is the rest of the lost draw weight coming from? We will know more when we measure the material properties of the pieces from Arvin’s stave. I don’t expect this to be a major contributor. I’m sure it would be very noticeable if the stave was significantly sub par.
A couple more pounds may have been lost if the bow took some set. There is still at least 5 pounds missing draw weight to account for.
Alan
-
The missing 5# you are trying to account for is on his shop floor.
-
(R :) now that’s funny Chris. Pappy
-
I’m sure pearl is right cause I missed the measurements! 🤠🤠🤠🤠
-
Anytime I've missed weight it was easy to find the missing poundage. Either on the floor or stuck in my Shinto still :)
-
I think in glue vs natural growth rings is the density of the early ring which is where the sheer is happening. The glue joints don’t have sheer. I know that lams have early wood But they don’t run the entire length of the bow. So if we did not have early wood where would the sheer happen Arvin??? Good question?🤠🤠
-
The difference between a 50# design and 35# real bow is too great to easily explain away with a typical amount of variation in material properties.
I agree. Wood is inconsistent, but not that inconsistent. I wasn't really suggesting all of the difference was in the wood.
A couple more pounds may have been lost if the bow took some set. There is still at least 5 pounds missing draw weight to account for.
That's 10% of your target weight and I have seen different pieces of the same species of wood vary that much in MOE, so some of the rest of your answer may be in there, along with any dimensional discrepancies. I wouldn't be surprised if the wood turns out to be a bit lower MOE and the limbs a touch thin to get you that last 10%.
The missing 5# you are trying to account for is on his shop floor.
;D That's very possible.
Losing 5% off the target weight only requires being under in limb thickness by 1.7%, which is around 0.010" or so on this weight of bow. Combine that with the wood being a bit less stiff and you get to 5# pretty easily.
Mark
-
The missing 5# you are trying to account for is on his shop floor.
lol, but dont most bowyers find that some woods "loose more poundage" than others when tillering, even without taking visible set due to the compaction or hidden set that happens as wood is worked at stresses near the max?
I don't expect this behavior to be well quantified in typical wood strength of materiels studies, as wood is almost always used at much lower stresses. Even airplane fuselages and sailboat masts have higher saftey factors in their designs than most bows, let alone bows for flight shooting.
-
For those who are curious, here are the correct osage material properties, based on the average of a number of samples I measured a couple of years ago.
Elastic modulus (bending): 1.87 Mpsi
Bending stress at “yield”: 15000 psi. This is approximately the point where higher bending stresses produced some noticeable set. Strain at this point is about 0.79%.
Ultimate stress at failure: 20000 psi
Density: 50.5 lb/ft^3
Alan