Primitive Archer
Main Discussion Area => Bows => Topic started by: Tuomo on October 13, 2025, 10:51:49 am
-
My newest bow, deflex-reflex bamboo (moso) backed, maple and ipe core, horn belly. It has osage powerlam, maple handle, white horn nocks and leather handle. Draw weight 98 pounds at 28 inch draw. Unfortunately, it is a bit too heavy for me...
Length is 156 cm (61,4") n/n, width 36 mm (about 1 3/8") and thickness after the power lam 15 mm (about 5/8"). Power lam length is 500 mm (about 20"). Weight is 695 grams. It took only about 20 mm (about 3/4") set.
I made the belly lam from five piece: in the middle is ipe (about 20 cm (8")), then horn and at the nock some osage. Belly lam and core are tapered before glueing, belly 0,002 and core 0,004. The taper was almost perfect, because the bow didn't need tillering, just width tapering and few strokes with a scraper.
I have not yet got any speed readings but watching a test shooter shooting with this bow, it seems to be quite fast..
-
More photos:
-
More:
-
Incredibly beautiful bow with perfect tiller. Too bad you can't shoot it but I'm not surprised at 98#. Well done! :OK
-
Thanks! I made two of these. First time I used horn as a belly material in this kind of deflex-reflex design (I have made some turkish sinew-horn-bows), so I made a tiny error estimating the correct thickness. The other one is almost identical but 70#@28". It is shootable and hopefully this one is also in some day!
-
Beautiful and interesting...
Del
-
That is a beauty for sure in all aspects, about twice to much weight for me 😊😉 but beautiful work just the same. Pappy
-
Ditto what the others have said, beautiful bow!
-
What a beautiful beast!
-
very nice
First time I used horn as a belly material in this kind of deflex-reflex design.........
I can not recall ever seeing horn used in a R-D design before. experimental?
Please let us know how it performs.
-
Nice bend! Beautiful Bow
Just 55lbs lighter +- and you would be right in my wheelhouse. :)
-
snice.
-
Hey tromo, I really love this bow, can you tell me what formula you used to for the bamboo, wood core and horn for this build?
I use to build glass bows, and used a certain thickness for the glass, and a tapered core, and I would like to build one like this.
Thanks Wallski
-
Seen this, and the lighter one also, and held them in my hands. They are real eye candies and shoot fine.
-
Outstanding!
-
Hey tuomo, I really love this bow, can you tell me what formula you used to for the bamboo, wood core and horn for this build?
I use to build glass bows, and used a certain thickness for the glass, and a tapered core, and I would like to build one like this.
Thanks! There is no special formula. I made a mild deflex-reflex form, modelled with a VirtualBow -program. Then tapered the bamboo just by feeling, core with a tapering jig (0,004) and belly with another tapering jig (0,002). So nothing special. I have made a lot of bamboo backed laminated bows and this was "easy" to make. One reason was that horn belly is very reliable (or I hope so...), because it tolerates a lot of compression. Osage would has been an other option but it would has taken a lot more set. I have also ipe but its elastic modulus is so high that it is hard for bamboo backing. I will make one or two 45–50# similar bows for everyday use. I belive that the bow might be quite good in long term use.
I have a chrono but I don't have yet stiff enough test arrows for this bow, I have to make some. And then I have to tune my shooting machine for testing. Hopefully I will get soon some chrono readings, this seems to be a fast bow!
-
Great Job Tuomo!
I sold a bunch of these in different designs over the last 3 years and they do all fine. It's a great combo - and as you mentioned, wood is a bitch compared to horn and makes bowyers life pretty easy. It's more elastic than any wood and takes away stress from the back.
However, that drawweight....(-; not bad. I have identified the bamboo as the weakest part.... had it failing a few times and decided not to make them more than 50#. So I'm a little impressed now (-;
However I see, you went pretty conservative, not putting net-reflex into. I work with 6-8" glued in reflex which seems to bring a lot of bending stress into the bamboo...
Congrats! Nice to see the concept spreading.
-
Nice bow! And nice to see that someone else has been making similar bows. Do you have link here in the forum to that bow, to see length, width, etc. specifications?
"I work with 6-8" glued in reflex which seems to bring a lot of bending stress into the bamboo..." – That is the reason I used very mild reflex. And playing with VirtualBow -program, it seems that too much reflex is just too much stress for the extra fps. More reflexed bow is a bit faster but usually too overstressed. In long term, gentle deflex-reflex form us usually the best.
Did you use moso-bamboo? I think that madake would be better option; at least japanese traditional yumi-makers consider that moso is too brittle and madake is the best of bamboo backings. I have some madake, I have to use it for next bows.
Maybe I have had just luck with moso, and this bow has under 50 full draws. It tells yet nothing, after 1000 full draw you will see how the bow last. But this is "nice to have" -bow, to give someone to draw and surprise!
-
I don't think I have posted about this specific bow here. It's 50#28" and measures somewhat 66"ntn I think and its around 36mm wide. I generally make these 64"-66" and around 33-36mm in width.
I do play with virtual bow from time to time and I'm always impressed of how exact it can mirror reality. It's an eye opener in many aspects. When it comes to reflex you are probably right about heavy bows. With light bows reflex helps a lot with performance imho. Best think about is the higher initial string tension and the resulting smooth drawcurve. I just love that. With heavy bows I wouldn't recommend either - these also don't need that little + in energy storage.
I have also heard that Madake was superior to Moso. But when I buy my bamboo from the big bamboo trader he sells me "Moso (Madake)" hahaha....still confused.... 8)
-
Wow. What a beautiful bow. Like everyone else, I don’t know anybody that could shoot it at 98# though.
-
Id like to see how far that bow can shoot. It would be an interesting contender for the Primitive complex composite unlimited category in flight shooting. I am certainly standing by for the chrono numbers Tuomo.
-
You are right Sleek! I think Jim Martin has that record now with one of my bow designs. That could definitely be in the hunt for both broadhead and flight!!!!!! You should get the bow into someone’s hand that can pull the weight.
-
Im real close to able. Ill certainly be able to next year.
-
Outstanding!
X 2
-
Wow
Beauty indeed even tough that draw weight could not be enough to kill those pesky Trex ;D
-
Gorgeous work. Those tip overlays are some of the prettiest I've ever seen.
-
Really nice bow. Beautiful tiller.
Bjrogg
-
Toumo, I want to congratulate you on winning Bow Of the Month with this build! Thank you for joining in and I look forward to future builds from you as well!
-
Outstanding bow and great designs. I’ve also made a few of these albeit lower poundage! They hold up well and shoot quite fast. I’m relation to the mosso bamboo I’ve done a mild heat treatment on mine on the fleshy side to really get it to the limits of strength and remain conservative on robust strength. I leave the nodes intact. Congrats on your win too. Very nice indeed
-
That is a pretty bow
-
I don't know how you keep the handle from popping off at that heavy weight? Is it pinned?
-
No, just glued with SmoothOn.
In fact, I don't know if it will stay or pop. I am not able (yet) to shoot this bow, so it is not really a problem yet.
-
Generally speaking, when a handle pops off of a self bow, at least, it's because there is movement(bending) in the handle and no amount of glue will prevent that. You might try wrapping it with sinew or another strong thread. I've been successful at doing that. On your next one try adding a power lam to prevent the handle area from bending.
-
This bow has an osage power lam. I use a power lam in every laminated bow — it’s a nice detail and also helps prevent the handle from popping out. A thin and long strip between the belly and the handle piece is also a good option. Most problems occur when the handle piece is ipe or another very rigid material, because it doesn't bend with the bow.
-
I think it is right and proper that the VERY FIRST new Bow of the Month Award goes to an absolutely exemplary showpiece of mastery of the art and craft.
No, this isn't my cup of tea, but in this case, I am no fool. I cannot help but admire the fine lines, the clean glue lines, the aesthetic and functional choice of materials blended together into something this side of perfection. I look back at the other comments, and I am pleased that most are from bowyers far better than I with knowledge and skills well beyond my abilities. They recognize the workmanship, too, they that are far less likely to be fooled by looks over execution.
Tuomo, you have earned some bragging rights with this bow. Congratulations.
-
I chronoed this bow. With a light 463 grain arrow (about 5 gn/#) the result was 256 fps. Quite ok, I am happy. Shot with a shooting machine, witnessed by my friend.
-
I chronoed this bow. With a light 463 grain arrow (about 5 gn/#) the result was 256 fps. Quite ok, I am happy.
That is good speed!
-
256fps is certainly on the HOT side of things. Thats fast! Especially with a 460 grain arrow. Id like to see what it will do with a 320 grain arrow.
-
256fps is certainly on the HOT side of things. Thats fast! Especially with a 460 grain arrow. Id like to see what it will do with a 320 grain arrow.
It should do around 300 fps. Maybe a little less.
-
256fps is certainly on the HOT side of things. Thats fast! Especially with a 460 grain arrow. Id like to see what it will do with a 320 grain arrow.
Based off of energy storage the 320gr arrow will go ~308fps if the bow efficiency stays the same. It will likely drop a bit with the lighter arrow, so figure on a bit less.
Mark
-
If he is storing 100% of draw force it would put his virtual mass at about 200 grains. Giving him around 285 for 350 grains. If he is storing less energy he would have a lower VM and have a higher speed.
-
If he is storing 100% of draw force it would put his virtual mass at about 200 grains. Giving him around 285 for 350 grains. If he is storing less energy he would have a lower VM and have a higher speed.
It doesn't matter how much energy is stored because it is the same for both arrows. To get the velocity for the 320gr arrow you simply equate the kinetic energy of both arrows and solve for the velocity of the lighter arrow. That assumes the efficiency stays constant, which it likely doesn't, so the lighter arrow won't quite get to the calculated speed.
Mark
-
You are wrong the best predictor of speed over an assortment of different weight arrows is virtual mass, which is based on stored energy and efficiency. The lower the virtual mass the less drop in ke as arrows get lighter.
I would guess that this bow probably stores about 93% or in that area. In that case his virtual mass would be lower and his arrow speed might be closer to 300.
-
I chronoed this bow. With a light 463 grain arrow (about 5 gn/#) the result was 256 fps. Quite ok, I am happy. Shot with a shooting machine, witnessed by my friend.
Do you mind solving a debate and making a 320 grain arrow to chronograph?
-
There is no debate because we don't know how much energy the bow stores; we can only guess at this point. Using virtual mass to predict arrow speed is not debatable; it has been used for decades. Now, just for fun, if he shot, say a 700-grain arrow and then let us guess the speed of the 320 it would be fun. I thought you said 350, I will go back and figure it at 320 with 160 grains VM and see what it comes to.
Ok my official guess is 292
-
You are wrong the best predictor of speed over an assortment of different weight arrows is virtual mass, which is based on stored energy and efficiency. The lower the virtual mass the less drop in ke as arrows get lighter.
I assure you that the laws of physics say what I wrote is 100% correct. The only question is how much the efficiency (as defined by what percentage of the stored energy is transferred into the arrow) changes between the two arrows.
Is there somewhere that explains how you calculate virtual mass?
I would also enjoy seeing OP test a few different arrow weights (if possible). It would make for an interesting experiment.
Mark
-
Is there somewhere that explains how you calculate virtual mass?
Mark,
If this is the definition that Steve is referring to, it seems to be a derived unit of measure describing bows.
https://www.archerylibrary.com/books/hickman/archery-the-technical-side/klopsteg/physics-of-bows-and-arrows/virtual-mass-of-a-bow.html
-
Virtual mass is easy to calculate. It helps if you know the stored energy but if you don't you can usually get it by shooting a few different weight arrows.
Here is how to calculate it. His bow shot 256 fps with a 463 grain arrow. You go to a KE chart and look it up It shows 67.39 ft pounds. Lets say I estimate the bow is storing 93% of draw force. So it would be 93% X draw weight ( 98# ) That would give me 91# of stored energy. So now I simply add enough imaginary weight to the arrow that we know the speed of which is 256 fps to give me 100% efficincy. On the icase if I add 160 grains to the 463 grain arrow and then check the ke at 256 fps it will give me about 91 Ft#. So to check speeds of arrows I have not shot simply add 160 grains to the arrow I want to the know the speed of. So if I want to know how fast a 320 grain arrow would be I add 160 to 320 and see what speed gives me 91 ft#. So 320 + 160 + 480. How fast would a 480 grain arrow have to be to get 91. The answer would be 292 fps.
I am guessing at the stored energy in this case because I only hvae 1 arrow sample. If I had two samples I could be a lot closer. A 250 grain arrow should do about 316 fps.
-
Virtual mass is easy to calculate.
Thanks for that explanation. Your method is using the same basic math as I used (since the laws of physics are the same for everyone), but keeping the virtual mass the same over different arrow weights builds in a proportional change in efficiency on top of the basic physics equations solving for the velocity with efficiency unchanged.
I hope OP can do some testing to see how close it all works out.
Mark
-
I will, of course, be back later!
-
Lets say I estimate the bow is storing 93% of draw force. So it would be 93% X draw weight ( 98# ) That would give me 91# of stored energy. So now I simply add enough imaginary weight to the arrow that we know the speed of which is 256 fps to give me 100% efficincy. On the icase if I add 160 grains to the 463 grain arrow and then check the ke at 256 fps it will give me about 91 Ft#.
A virtual mass (K) of 160 would put this bow above the top of the highest K curve on Klopstegs chart.
Have you ever tested a bow with lower virtual mass? If so, what did it calculate out at?
from the article quoted above
-
Very short bows will often have lower virtual mass figures. Tuomos bow was kind of exceptional with the speed he got. The short bows also store a lot less energy. The primary reason I liked to use virtual mass was to isolate hysteresis from vibration. Self bows will rarely, if ever, go along with virtual mass theory because the hysterisis caused by set is time sensitive and the faster the bow shoots the more the losses are from hysterisis. Glass bows on the other hand Will stick very close to VM projections but still trending slightly slower. I had an odd way of calculating stored energy and VM, most experts don't agree with it, but numbers seem to follow more reliable patterns. I would use an extremely heavy arrow to test the speed, maybe 2,000 grains, and then I would go to 1,000 grains, and then 500, 300, then 200. The 2,000 grains would almost always reflect about 95% efficiency so it was a good starting point. I no longer remember the exact process, but it was fairly simple, and I felt it gave me more useful information about the damage from set. Tuomos bow doesn't act like a bow with hysteresis. Isolating and identifying where losses in energy occur gives the bow maker more opportunity to improve.
-
Tuomos bow doesn't act like a bow with hysteresis.
I would suggest that is because it uses horn on the belly and it is not subject to the same hysteresis problems as wood.
We really need a like button on this forum, there has been some great info posted in this thread.
Mark
-
Beautiful bow! Outstanding craftsmanship. Thanks for posting the photos here
-
256fps isnt bad I'd say (-;
why didn't you test te magic 10gpp for us? you didnt' have that 1000grain arrow? :)