Primitive Archer
Main Discussion Area => Bows => Topic started by: Eric Garza on September 24, 2020, 10:56:33 am
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I finished my first deflex-reflex self bow the other day. It was made of hickory and is 67 inches tip to tip. It draws 50 pounds at 25 inches (I use a floating anchor, so have no need for the bow to draw a full 28 inches), and does not feel that heavy at full draw. It turned out okay, though there are many things I will do differently when I tackle my second d-r bow.
With that in mind, I am curious if the d-r design adapts well to shorter self bows. I recall that Marc St Louis posted years ago about a short bamboo-backed yew d-r bow that he felt did not perform all that well. Any other data points out there? By short, I am thinking in the 50-60 inch range. My next project will probably be a 55 inch bow, and I might invest the time to make it a deflex-reflex if it seems like the performance benefits hold at that short length.
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I enjoy just straight reflex,, maybe I am lazy and its a bit easier to make,, and shoots fine for me,,even in the shorter 50 inch versions,,sinew backed,, Im sure the reflex deflex would be great, I dont think there would be alot of difference in performance cast wise,, but others that make that design can chime in,,
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Brad,
is there a case to be made for deflex in the design to help get a decent brace height with a 55" reflexed hickory bow?
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im sure there is, and feel like I have read that, I just dont have experience with it,,or have not tested that design,,the brace height has never been an issue for me,,and I love to shoot short bows
I remember DC posted some graphs that showed string angle on rd ,, and there was a good discussion on that thread,,
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I just finished a 52" RD that is about 35#@25". I think it was 187@10gpp. I used the same caul I use for the 66" bows, I just slid it out to the end. I think all the R cancelled out most of the D. Think the short ones need their own caul. :D I'm going to do some comparison testing with short drawing my 50#@28" bow this afternoon. I'll post the results.
Sorry for the blurry pic but you can see the shape.
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that seems very effecient for the 25 inch draw,, I remember a full draw curve you did with the longer bow, and I think it was like 175 for 24 or 25 inch draw,,since the bow was not designed for that draw I thought it was great,, I think that bow went to 200 fps with the 28 inch draw
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I'm thinking that the little bow should be faster up to a point as it has a lot lighter limbs. We'll see.
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I love the profile of the little bow, very graceful,,
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im sure there is, and feel like I have read that,
yes, I spoke a bit soon, sorry. Trying to do too many things at once today. and follow along. guessing my concern would matter if we knew a bit more.
Eric, what brace height and drawlength are you shooting for?
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Well so much for that. It was fine the other day and I did a little sanding(very little) and today one limb is way weak. Boy these things can be finicky. A weeks work and then one scrape too much and they're toast. I'll glue a splint on it just to see what could have been. Sorry no tests.
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:(
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Eric, what brace height and drawlength are you shooting for?
I typically use a brace height of about 5 inches, and my draw length is 24-25 inches, depending on shooting position.
The bow DC showed looks sweet. I do not think I would try for that much reflex, but the idea of a 52-inch D-R bow intrigues me. That one looks like a laminate. Mine would be a self bow, probably made from either HHB or Osage.
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Yes it's Boo backed Yew. I've had difficulty getting selfbows to hold enough reflex for the speeds that I'm after.
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yes they are tricky,,
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Yes it's Boo backed Yew. I've had difficulty getting selfbows to hold enough reflex for the speeds that I'm after.
That is good to know.
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You do an amazing job of holding the reflex you hold. Are you familiar with establishing virtual mass on your bows? I think you would find it helpful in your testing.
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If you're talking to me I'm not familiar with any of the math but I'm thinking I have to learn.
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Yes, I was talking to you LOL. It is a good way to identify hysteresis in your bows. A glass bow has very little hysteresis so once the virtual mass is established it will remain fairly constant regardless of arrow weight even though efficiency will continue to drop with arrow weight. A wood bow that has taken set will display more hysteresis and because set is time sensitive it increases rapidly as arrow weights go down. The math is very basic and I even have a cheat I use to speed things up a bit on taking force draw curves. I will get back to you in a few minutes with the details or I can e email them to you if you prefer.
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To make this sort of bow it makes sense to use some billets. Reflex and heat treat them then splice in deflex. You should aim to end up with around 1 - 2" overall reflex once spliced.
This design is perfect for a short draw/short bow. Very stable to shoot and fast.
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Yes, I was talking to you LOL. It is a good way to identify hysteresis in your bows. A glass bow has very little hysteresis so once the virtual mass is established it will remain fairly constant regardless of arrow weight even though efficiency will continue to drop with arrow weight. A wood bow that has taken set will display more hysteresis and because set is time sensitive it increases rapidly as arrow weights go down. The math is very basic and I even have a cheat I use to speed things up a bit on taking force draw curves. I will get back to you in a few minutes with the details or I can e email them to you if you prefer.
You might as well put them here, others may be interested. I will save them :D
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You might as well put them here, others may be interested.
I would be interested also Steve.
A wood bow that has taken set will display more hysteresis and because set is time sensitive it increases rapidly as arrow weights go down.
very well spoken.
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I will try and explain the best I can. Virtual mass is the amount of weight difference between a tested arrow and an arrow shot at 100% efficiency to reach the same speed as the test arrow.
Example: DC shoots a 500 grain arrow from a 50# bow and hits 200 fps. This imparts 44 ft# of Ke into the arrow. DC has done a force draw curve on the bow and found that he is storing 55 ft# of energy. Using a KE calculator he starts adding virtual weight to his arrow until it reaches the full full 55# of stored energy at the same speed as the 500 grain arrow. In this case 620 grains of arrow traveling at 200 fps would store 55 ft# of KE. So the virtual mass of his bow would be about 120 grains.
The interesting thing about a wood bow is that if the bow has no hysteresis the virtual mass will remain relatively constant regardless of arrow speed and arrow weight. Being that hysteresis is speed sensitive a bow that has taken set will exhibit more hysteresis, your virtual mass will rise as arrow weights decrease and it will go down as arrow weights increase.
one of the cheats I mentioned was to use an extremely heavy test arrow to determine your stored energy instead of measuring a force draw curve. A 2000 grain arrow should give you about 95% efficiency. You may have to play with it a little to nail it down but I believe 90% is pretty close. This will vary with different bow types so if you are working with the same style bow it should get you pretty close once you nail it down.
Lets say your 2000 grain arrow shoots at 106 fps and gives you about 50# KE add 10% to that and you most likely have about 55# stored energy. You are looking for a consistent number on your virtual mass with a variety of arrow weights. Ideally it will only rise slightly as arrow weights decrease.
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So what do I use virtual mass for?
I found a KE calculator here. https://www.calculatorsoup.com/calculators/physics/kinetic.php
Is adding up all the squares and part squares more accurate than a heavy arrow?
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So what do I use virtual mass for?
I found a KE calculator here. https://www.calculatorsoup.com/calculators/physics/kinetic.php
Is adding up all the squares and part squares more accurate than a heavy arrow?
I like the heavy arrow method but you do have to get dialed in on it by using the long method first. Once you figure out what percentage to use you should be good to go. Virtual mass is a good way to predict speeds of various weight arrows.
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Yes it's Boo backed Yew. I've had difficulty getting selfbows to hold enough reflex for the speeds that I'm after.
Dc, what speeds are you after?
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As fast as I can ;D ;D
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Virtual mass is a good way to predict speeds of various weight arrows.
Isn't that what I bought two chronos for?
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thanks Steve
you compare an arrow to an ideal arrow and the mass difference is attributed to the bow?
example: my new bow has a Virtual Mass of 123grains. or do you need to say: my new bow has a Virtual Mass of 123grains @ XX grains per pound?
if bows loose efficiency as arrows get lighter, then where is the benchmark in arrow weight?
Virtual mass is a good way to predict speeds of various weight arrows.
once you determine the VM of the bow, how do you figure speeds for other weight arrows?
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thanks Steve
you compare an arrow to an ideal arrow and the mass difference is attributed to the bow?
example: my new bow has a Virtual Mass of 123grains. or do you need to say: my new bow has a Virtual Mass of 123grains @ XX grains per pound?
if bows loose efficiency as arrows get lighter, then where is the benchmark in arrow weight?
Virtual mass is a good way to predict speeds of various weight arrows.
once you determine the VM of the bow, how do you figure speeds for other weight arrows?
Knowing virtual mass is a good way to identify where your losses are coming from. All bows loose efficiency with lighter arrows but the virtual mass will remain fairly constant if losses are not from hysteresis. The only thing that causes hysteresis in wood bows is set or high moisture.
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I feel that I'm missing something here. Is a higher VM better or worse? Could I use this number to compare two bows to see if one took more invisible set than the other?
Sorry for hijacking your thread Eric. That wasn't the intent.
PS Does the "Technical Archery" site do a decent job of explaining this
https://sites.google.com/site/technicalarchery/home
I read the "Virtual Mass" section and saw a glimmer of understanding.
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Dc, what speeds are you after?
I think you deserve a better answer. I seem to be caught in an arms race with myself. Since I hit 200 anything that doesn't reach that mark seems like a failure. I'm throwing bows that shoot 195fps in the corner of shame. This is wrong and something in the back of my mind says that I should get back into the "art" part of this hobby. I just get obsessed with stuff that catches my interest. That's my fault.
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DC, I think what you are doing is very important much more so than you realize. It will have ramifications that reach into the modern bow world as well. You have been good about giving Mark St Louis full credit for his designs and I respect that immensely. We will never know for sure if Mark was reaching those speeds with his bows because his testing was not as formal as yours. I would like to see the elements of his designs that you are concentrating on looking for more speed? Extremely skinny strings are most likely giving you about a 5 fps boost. I don't believe that many woods besides yew could give you the same results as yew has almost double the elasticity over most woods and you seem to have done an outstanding job of utilizing the yew wood to its potential. Just hearing about your program of chasing this speed I think is worthy of some attention.
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Well thank you Badger. I just wish I understood more of what was going on.
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I'm throwing bows that shoot 195fps in the corner of shame. This is wrong..I just wish I understood more of what was going on
have you considered putting some of those bows in the hands of other shooters and letting them give you feed back?
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I'm throwing bows that shoot 195fps in the corner of shame. This is wrong..I just wish I understood more of what was going on
have you considered putting some of those bows in the hands of other shooters and letting them give you feed back?
I think he uses them to experiment with later...
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Sorry for hijacking your thread Eric. That wasn't the intent.
No problem at all. This is all very informative.
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Dc, what speeds are you after?
I think you deserve a better answer. I seem to be caught in an arms race with myself. Since I hit 200 anything that doesn't reach that mark seems like a failure. I'm throwing bows that shoot 195fps in the corner of shame. This is wrong and something in the back of my mind says that I should get back into the "art" part of this hobby. I just get obsessed with stuff that catches my interest. That's my fault.
I understand well. Im doing the same thing from the self bow standpoint. I've hit 184 fps with mine, though in not r/d in design, and im now looking to hit 190s with the same design and only pulling 26 inches.
My failures are still darn good bows, and I keep them to experiment with and tweak. I have 2 im going to back, one with sinew and the other bamboo.
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I'm throwing bows that shoot 195fps in the corner of shame. This is wrong..I just wish I understood more of what was going on
have you considered putting some of those bows in the hands of other shooters and letting them give you feed back?
I think he uses them to experiment with later...
Freight, customs, the fact that they're all cobbled up with patches and yes, I do sometimes modify them.
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when you are an artist,, nothing is wrong,, :)
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I understand well. Im doing the same thing from the self bow standpoint. I've hit 184 fps with mine, though in not r/d in design, and im now looking to hit 190s with the same design and only pulling 26 inches.
Sleek, what design are you using if not r/d? You have my attention.
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Also intrigued by your mention of a shorter draw. I have been looking at a lot of force-draw curves, and been thinking that reducing draw length down to the inflection point where you see the transition from the region of declining slope to the region of increasing slope. Depending on side view profile and overall bow length that often happens around 21-25 inches on most of the bows I have made and measured.
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I understand well. Im doing the same thing from the self bow standpoint. I've hit 184 fps with mine, though in not r/d in design, and im now looking to hit 190s with the same design and only pulling 26 inches.
Sleek, what design are you using if not r/d? You have my attention.
I use a recurve that is deflexed in the handle, then reflexed through the limb, ending with hooks at the tips. I did steal from a the typical R/D design, but with the addition of recurves, I dont think it falls into the R/D category any more, though without the recurve, it would resemble an R/D. Its a short bow design, only 54 inches long, and fits my 26 inch draw very well. 26 inches draw isn't anything I came by scientifically, its just my draw, so I designed this bow entirely around my draw length. Im shooting 184 fps right now with it, and believe strongly i can hit 190s with the same design.
I plan to go to 28 inches draw with a 58 inch bow eventually as i think thats the ideal bow length for that draw, and have a dream of hitting mid to upper 190s with a self bow.
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Also intrigued by your mention of a shorter draw. I have been looking at a lot of force-draw curves, and been thinking that reducing draw length down to the inflection point where you see the transition from the region of declining slope to the region of increasing slope. Depending on side view profile and overall bow length that often happens around 21-25 inches on most of the bows I have made and measured.
I believe, if I understand you well, my design is right on the edge of that, however I hadnt though of this angle of perspective. I am still trying to fatten my curve and for now, its very flat.
Eric, what length bow do you typically make?
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Most recently I have been playing with bows that are about as long (tip-to-tip) as I am tall, so about 67 inches. They shoot well and draw smooth, but the areas I hunt have lots of brush which makes getting a clean draw and release a challenge sometimes.
If I averaged all of the bows I have made, the length would probably be around 55 or 56 inches. I enjoy hunting with shorter bows more than longer ones, and of course it is easier to find (and cheaper to buy) nice, straight, clean short staves than it is finding longer ones.
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Also, Sleek can I assume the fps numbers you are reporting are for 10 gpp arrows? Those are solid arrow velocities for such a short bow. You are obviously doing a lot of things right.
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Also, Sleek can I assume the fps numbers you are reporting are for 10 gpp arrows? Those are solid arrow velocities for such a short bow. You are obviously doing a lot of things right.
I had been gearing up and focusing entirely on the flight shoot I just came back from and had completely slipped my mind about the 10gpp reference. The arrow for the broad head shoot is 450 grains and we shoot a 50 pound bow. So, no, mybarrow and speed i gave you were NOT 10gpp, but 9 gpp. So im upper 170, right close to 180 fps with a 10gpp. Im sorry for being misleading there, I guess I just hadn't switched my brain off from the flight shoot yet.
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Most recently I have been playing with bows that are about as long (tip-to-tip) as I am tall, so about 67 inches. They shoot well and draw smooth, but the areas I hunt have lots of brush which makes getting a clean draw and release a challenge sometimes.
If I averaged all of the bows I have made, the length would probably be around 55 or 56 inches. I enjoy hunting with shorter bows more than longer ones, and of course it is easier to find (and cheaper to buy) nice, straight, clean short staves than it is finding longer ones.
id like to see your shorter bows and what performance you get from them.
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Sleek when you measure a recurve do you follow the belly? The 52" one I made(following the belly) seemed like it was bent awful tight at 24". With the handle and the recurves there's not a lot of limb left.
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Sleek when you measure a recurve do you follow the belly? The 52" one I made(following the belly) seemed like it was bent awful tight at 24". With the handle and the recurves there's not a lot of limb left.
Yes I follow the back actually. Really I start with a 54 inch stave and go from there.
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Same as I did. Mine is 52". I guess the big hooks used up too much working limb.
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I recall that Marc St Louis posted years ago about a short bamboo-backed yew d-r bow that he felt did not perform all that well. Any other data points out there? By short, I am thinking in the 50-60 inch range. My next project will probably be a 55 inch bow, and I might invest the time to make it a deflex-reflex if it seems like the performance benefits hold at that short length.
The bow I made, actually there were 3 bows of a similar shape, had a lot of deflex in the handle. I made these bows so that they are short but can handle a 28" draw and I think it was this amount of deflex which compromised performance. That amount of deflex introduces unwanted problems
These are a couple of the bows I am referring to
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Marc, so you think a more modest amount of deflex would have benefitted the bows? How much handle deflex do you think would be ideal for a R-D self bow?
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Those are the bows that got me going. I use about 11° deflex and I did a quick measure off the screen, so it's not that accurate, and Marc's are in the 30-35° range. The limbs look very similar.
Beautiful bows Marc
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Marc, how long are those bows? What performance were you getting from them, and have you made any that are self bows?
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Yes less deflex is better for performance but then the limbs start to suffer at the longer draw. i think the ideal is around 10 ~ 15 degrees
Both of those bows are in the low 50" range
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I assume lower deflex would be easier on the limbs with a shorter draw then? 24 or 25 inches rather than 28?
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With short bows yes. There's only so much stress wood will take, short working limbs equals short draw
have you made any that are self bows?
This is the first highly deflexed bow I ever made. It was an Osage selfbow that was 56" long overall and pulled 65# @ 28". If I was to re-make such a bow I would change certain things, the recurves are way too big