Primitive Archer
Main Discussion Area => Bows => Topic started by: Tommy D on May 31, 2021, 09:15:22 am
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I want to glue up a bamboo backed, ash cored, ipe bellies trilam. I have made a R/D form out of mdf. It has about an inch of deflex and 2 of reflex and the curve to reflex starts about 1/3rd between the handle and tip.
Length is 66” and it is a pyramid design from 1.25” to .5” at the tips. I have tapered the ash core. I have also ground the bamboo backing to a “knife edge” ... so it will also by default have some thickness taper.
I am thinking of gluing up the belly lams on top of the handle/ riser the way it is done with a glass bow.
Do I need a “power lam” between the bamboo and the ash core?
Please feel free to point out other glaring design flaws. I have a thick skin!
Some photos ...
(https://i.imgur.com/SS8VXke.jpg)
(https://i.imgur.com/bNHKbsV.jpg)
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With the handle riser sandwiched between the back and belly lams you probably don't need a power lam. For insurance you could add a thin lam that goes out beyond the riser on each limb. 1/8" to 1/16" should be plenty if needed at all.
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Not to help answer your question, but to ask you a question... I've made quite a few BBOs just using various sizes of blocks, but have thought about using one of my RD forms like yours. How do you plan to allow for the nodes when doing the glue-up? I've thought about some type of pressure strips between the nodes to make the surface flush...but haven't tried it. If you flatten the boo, then lay out your pattern on the flat side, cut it out to shape (a little proud) before your do the thinning...then the edge thickness will remain pretty constant for your finished bow and you can actually pre-tiller the backing somewhat...plus it gives you the pattern to follow when shutting out the bow shape. Looking forward to watching your project. :OK
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Not to help answer your question, but to ask you a question... I've made quite a few BBOs just using various sizes of blocks, but have thought about using one of my RD forms like yours. How do you plan to allow for the nodes when doing the glue-up? I've thought about some type of pressure strips between the nodes to make the surface flush...but haven't tried it. If you flatten the boo, then lay out your pattern on the flat side, cut it out to shape (a little proud) before your do the thinning...then the edge thickness will remain pretty constant for your finished bow and you can actually pre-tiller the backing somewhat...plus it gives you the pattern to follow when shutting out the bow shape. Looking forward to watching your project. :OK
I am not sure what I am going to do yet - but I understand the problem. I had thought of a foam strip that would contour to the bamboo.
What I will probably do is wrap the glue up in packing tape, which should apply enough pressure for the laminations to pull together and then use inner tube bands to make that follow the shape of the form. The bending of the lams to the shape of the form will no doubt squeeze the lams together more.
This is the theory anyways...
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Not to help answer your question, but to ask you a question... I've made quite a few BBOs just using various sizes of blocks, but have thought about using one of my RD forms like yours. How do you plan to allow for the nodes when doing the glue-up? I've thought about some type of pressure strips between the nodes to make the surface flush...but haven't tried it. If you flatten the boo, then lay out your pattern on the flat side, cut it out to shape (a little proud) before your do the thinning...then the edge thickness will remain pretty constant for your finished bow and you can actually pre-tiller the backing somewhat...plus it gives you the pattern to follow when shutting out the bow shape. Looking forward to watching your project. :OK
I am not sure what I am going to do yet - but I understand the problem. I had thought of a foam strip that would contour to the bamboo.
What I will probably do is wrap the glue up in packing tape, which should apply enough pressure for the laminations to pull together and then use inner tube bands to make that follow the shape of the form. The bending of the lams to the shape of the form will no doubt squeeze the lams together more.
This is the theory anyways...
That's about as far as I got when I thought about doing it too. I was concerned with pulling the bamboo down to the form in between the nodes, creating a wavy back/bow...maybe strips of a kindergarten napping mat?
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I did something somewhat similar except I just did 3 layers of ash with 2 power lams between each layer. I didn't use a riser. The power lams were 1/8". The back one was 18" long and belly side was about 12". I tillered to about 45#. After about 50 arrows the inside ash layer collapse at about the end of the long power lam. This may or may not help you, but make sure the transition is smooth or the bamboo will overpower the ash.
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I did something somewhat similar except I just did 3 layers of ash with 2 power lams between each layer. I didn't use a riser. The power lams were 1/8". The back one was 18" long and belly side was about 12". I tillered to about 45#. After about 50 arrows the inside ash layer collapse at about the end of the long power lam. This may or may not help you, but make sure the transition is smooth or the bamboo will overpower the ash.
A powerlam goes inbetween the back and belly.
Your form is good for a wood backed bow but not for a bamboo. Really the form is backwards for what you intend to do......
A powerlam is to stiffen the stack at the handle fades so that you can safely glue the riser stack directly onto the belly without risk of it popping off (and not waste a load of belly wood). So no you definately don't need one with a sandwiched riser.
If you go with your idea of riser posistioning make certain that you get a true feather edge to the fades for 1/2" or so. You should be able to hold the riser up to the light and see through it. If you don't do this you will get a poor glueline right where you don't want one!
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I have the other half of the form - maybe I will look at using that so the bamboo backing sits on the top side then.
Is pre-wrapping in packing tape still a good idea - or can the lams be glued straight up with inner tube
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And also would straight grained lumberyard ash hold up as a backing strip for Ipe?
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Pre-wrapping is a BAD idea! It will induce twist into your glue-up! Apply some packing tape onto the 'face' of your form to stop stuff sticking to it. Then get some parcel wrap (clingfilm) once the lams are glued and layed up on the form. Use a combo of parcel tape (sticky) and the wrap to make the lams comform to your form. They won't move once you have enough tape and them wrapped. Then apply your innertube wrap around the form and lams. Your first wrap should go from handle to tip. Once at the tip take another tube and wrap back towards the handle in the opposite direction. This way you illiminate any induced twist in your glue-up. Same on both limbs, 2 tubes per limb. Just cut the valve section out of the tube.
Straight grained ash is a great backing :)
Make sure your belly lam is thin enough to conform to the form....ipe is stiff stuff.
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I guess one way to deal with backings that are not uniform (bamboo/single ring backings) is to do the form the opposite way, so the belly (which will almost always be flat) goes against the form, and the inner tube/ wrappings go over the backing.
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(https://i.imgur.com/Wn3TV43.jpg)
Trilam glued up; 2 power lams; wrapped in packing tape and then 2 layers rubber inner tube wrapped in opposite directions to avoid limb twist. In the hot box now...
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nice profile and great form...looking forward to seeing it after the glue dries. What glue do you use?
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I am using Ampro epoxy from Gurit - only because I am pretty familiar with epoxy. Next one I will glue up with West G flex ... I am curious how much difference there will be ...
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interesting...I've never used either...back when I made lots of BBOs they still made URAC and it's all that I ever used. Thanks.
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This is the way I do it.I've got 2 bamboo backed mulberries to do soon here.These are'nt going to be tri lams but solid cores but don't see any difference in procedure.From a pre tapered slat core and 1/8" thick bamboo all cut to top view profile.
Before sizing with smooth on I sand with at least 60 grit and then I tooth[or lightly score length wise] both surfaces length wise with a hacksaw blade.Clean up little shavings etc.Do a dry fit and you'll feel it does'nt want to move sideways very easily at all.The light scoring helps prevent that.Put masking tape on back of bow and belly of bow.Then size with epoxy.Wrap in place intermittentantly with cling film.Then wrap completely with cling film.Then wrap completely with innertube strips.Then clamp to form and let cure.
Clean it up the next day and onto the tillering board.
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Ed - ask Smooth-On about using a toothing plane on lams :)
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Do you mean deeper furrowed toothing grooves of 1/32" or deeper?By toothing I really mean lightly scoring the surface with the teeth of the hack saw blade.I'll correct that.
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I didn't even know Smooth-On made bows.
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I'm not sure they do Pat.They do know bow makers use the stuff.They might leave that up to us guys experimenting with their product.
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I did not read the whole topic but
Go to lowes or Home Depot and look for these mats, cut the same width as the form and lay it on the form, get a 36" long mat and butt them together at the center.
(https://i.imgur.com/9OkvxKm.jpg)
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I did not read the whole topic but
Go to lowes or Home Depot and look for these mats, cut the same width as the form and lay it on the form, get a 36" long mat and butt them together at the center.
(https://i.imgur.com/9OkvxKm.jpg)
Thank - have you used this system?
I am also wondering whether people have glued on bamboo backs to bows using the air hose method that glass bows use?
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I know some that use it
you need to use steel pins and mule tape(pull tape) to lash down the fire hose on top of the bow.
A dry run will let you know how much air pressure you need
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A couple of my FG bow building friends use the hose on the form method.I think they use 70#'s of pressure on the gauge.
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Ok - so I have cleaned her up - she holds just under 2” of reflex, is 1 1/4” at fades to half inch wide at the tips. 65” ntn. I am going for 70# at 27”... I think she has a good shape and should pack some authority if I can tiller it right.
Bamboo back, ash core and Ipe belly.
I have her on the tillering tree and the long string.
She is at 70lbs in the “drawn” photo.
I think I want to start taking some wood off at the bottom of the belly - I can see the tips are already trying to come round and there is some movement out of the handle fades - but I know that this is a tricky thing to get right with R/D bows ... so am all ears ...
(https://i.imgur.com/r6on6Of.jpg)
(https://i.imgur.com/v6jhknA.jpg)
(https://i.imgur.com/Biz5heb.jpg)
(https://i.imgur.com/ipeqmge.jpg)
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With the pyramid limb profile and the reflex being mostly in the inner limb I think the full draw is going to look a bit funky. It’ll probably look like it’s bending too much in the fades with stiffer inner limbs and a bit more bend in the outer limbs. I’d watch for set and tiller based on that since the forces with that R/D profile can be tricky.
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With the pyramid limb profile and the reflex being mostly in the inner limb I think the full draw is going to look a bit funky. It’ll probably look like it’s bending too much in the fades with stiffer inner limbs and a bit more bend in the outer limbs. I’d watch for set and tiller based on that since the forces with that R/D profile can be tricky.
Thanks Ryan - any pointers as to what it should look like braced and at full draw. Am sort of thinking if the limbs are straightish at brace and then come round at full draw?
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It’ll be close to that but be careful that the reflexed portion isn’t bending too much by straightening out early.
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(https://i.imgur.com/DvMP8o5.jpg)
Still on the long string here at 60lbs.
Watching the set and so far unchanged.
(https://i.imgur.com/r1djDZA.jpg)
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I think it’s looking pretty dang good. Might be ready to brace.
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Tomorrow ... right now it’s time for that cold beer that’s been eyeing me up all day!
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Ok - I braced it - it’s 6.5” at the fades braced. It is a b#%h to brace.
I drew it to 24 inches - and it’s 60# there. These R/D bow really throw me off with such high early draw weight.
It’s a weird shape as Ryan predicted!
Unbraced it and it’s taken a little set - most of which I think is coming from where it turns back from deflex to reflex... I think?!
I suppose I want her bending a little more either side of this right?
I will not do anything till I hear from the experts!
(https://i.imgur.com/1GyzTBj.jpg)
(https://i.imgur.com/Pu02GOT.jpg)
(https://i.imgur.com/rctWvoZ.jpg)
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It’s probably pretty close to your goal of 70# currently. If the amount of set is reasonable you could pull to 70# and see where you end up. I think you might be able to squeeze the last inch or two out of the inner limb near the fades.
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Ok - I braced it - it’s 6.5” at the fades braced. It is a b#%h to brace.
I drew it to 24 inches - and it’s 60# there. These R/D bow really throw me off with such high early draw weight.
It’s a weird shape as Ryan predicted!
Unbraced it and it’s taken a little set - most of which I think is coming from where it turns back from deflex to reflex... I think?!
I suppose I want her bending a little more either side of this right?
I will not do anything till I hear from the experts!
(https://i.imgur.com/1GyzTBj.jpg)
(https://i.imgur.com/Pu02GOT.jpg)
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I honestly did not like the shape of your form I prefer the dip quite a bit further out toward the tips. But on the good side if you make it out to 28" it should be a fast bow. The profile is a bitch to tiller out as I am sure you are discovering.
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I honestly did not like the shape of your form I prefer the dip quite a bit further out toward the tips. But on the good side if you make it out to 28" it should be a fast bow. The profile is a bitch to tiller out as I am sure you are discovering.
I also thought that the dip was too far in - but I read somewhere from someone on this forum that having the dip in the inner third was the way to get a fast bow. They were also the ones recommending a form over the system with posts. I have to say that the form has really created a very even/ symmetrical bow shape - and they aren’t that hard to make.
I do agree though that most r/d bow images I looked at seemed to have the dip about half way.
I guess we will see how it shoots!
It’s not my favourite shape that’s for sure, but let’s see how it shoots.
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I've made very similar profiles.
I wouldn't touch mid to outers anymore but would get the rest of the bend from fades to mid.
my2c
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It’s probably pretty close to your goal of 70# currently. If the amount of set is reasonable you could pull to 70# and see where you end up. I think you might be able to squeeze the last inch or two out of the inner limb near the fades.
I am happy to trade a few pounds for better tiller - just don’t want to come in at 40#s trying to get there! I’ve definitely underestimated the early draw weight vs final draw on the R/D profile before
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I've made very similar profiles.
I wouldn't touch mid to outers anymore but would get the rest of the bend from fades to mid.
my2c
Many thanks - how do they/ should they shoot?
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You might loose a few pounds getting the bend more to the inners but you won't loose a lot of performace because you'll gain efficiency at the same time...
they are super fast and dry shooters - I like them a lot, especially on lower drawweights ;D
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Sound advice I would say.They do tiller different than regular side view straight or reflexed self bows as far as removal goes I think.
Full draw does'nt look to bad.
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The inner limbs are your widest part too and there’s not much change from the original profile so they can probably bend a bit more without taking set. Your outer limbs could also bend a hair more I think. Being a narrow pyramid taper without needle like tips, the tiller shape would have more bend in the outer limbs if a straight longbow profile.
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The inner limbs are your widest part too and there’s not much change from the original profile so they can probably bend a bit more without taking set. Your outer limbs could also bend a hair more I think. Being a narrow pyramid taper without needle like tips, the tiller shape would have more bend in the outer limbs if a straight longbow profile.
Do you mean more bend in outer limbs than a straight longbow?
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Is some set inevitable? Do glue ups like this invariably result in some reflex being pulled out? I’ve lost about 3/4 of an inch and am at 26 inches and 65 lbs ...
Gonna shape the handle and put some arrows through it, sand it and then fine tune anything...
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Is there a competition for the World’s Ugliest Bow on PA? I think I am really in the running with this one!
I’ve played with the tiller a little and brought it down to 60lbs at 27”. With hindsight I think my tips bent too much already for the poundage I was after and I think that I probably took too much off the where the deflex turns to reflex ...
I had pre- tapered both the core and the belly - if I ever use this form again, and profile, I won’t taper the belly wood.
All that being said, it’s so damn ugly I think I will make another form based on what I have learn, I would move the curve further out and I would also have more reflecting curve in the outers. These ended up very straight ... and I think contribute to the difficulty I had balancing the tiller.
I am wondering whether in an ideal world, at brace the bow should retain a slight reflex curve. This all came out as I tried to balance my overly weak tips with the poundage I was after.
Anyways .... it has pulled out about an 1 1/4 of the original layup, and it does seem to throw arrows just fine.
Been shooting some 750 grain arrows with 300 grain points and about 1 in 3 is blowing out the other side of my target ... so I shouldn’t be too disappointed with it I guess!
(https://i.imgur.com/6Ucpt0o.jpg)
(https://i.imgur.com/hizsAxq.jpg)
(https://i.imgur.com/OTe45Gg.jpg)
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Doesn’t look bad at all to me. Just different. I think if you were able to squeeze a bit more bend out of your inner limbs it could have saved some of the set in the mid/outer limbs. That being said it sounds like it’s a good shooter. Well done!