Instead of polluting the What Did You Do Today? thread with all my ramblings I figured I might as well put all this in its own thread. Maybe someone down the line will find it of some use.
First off, the form I am using:
(https://i.imgur.com/bTLTNZB.jpg)
(https://i.imgur.com/g5rADg2.jpg)
The spine is a 3.5" x 2.5" x 0.25" steel angle that was left behind at our acreage when we bought the place. The posts are 2x4 construction lumber that I milled up flat and cut a radius on so that I can clamp the bow to the post at any angle without the clamp twisting the bow. The adjustable posts let me experiment with many glue up shapes without having to continuously make new forms. If you know what profile you want to make a one piece form is a better way to go overall.
Note that all of what follows is mostly applicable to wood bows. The mechanics of it also apply to glass lam bows, but the glass lams are so strong that it is not particularly necessary or important for them.
For those that don't know what Perry Reflex is, read The Traditional Bowyer's Bible Volume 3, pages 91-95. What Dan Perry developed was a method of making lam bows where he would take the belly lam and pull it forward into reflex when gluing on the back lam. This results in a reflexed unbraced side profile. The effect of this was to preload the belly surface into tension on the unbraced bow. This preload has a couple of effects. First, it forces the core of the bow to store more draw energy than it normally would in a conventional flat bow. Second, it reduces the maximum compressive stresses on the belly surface at full draw. This reduces the amount of set a bow will take. Both of these improve performance.
The downside to doing this is it results in higher back stresses due to the reflexed side profile of the bow. There is also a limit to how much reflex you can have in a bow before it gets tricky to tiller and becomes difficult to brace without a lot of effort and equipment.
Mark
:thumbsup:
Now to my experimenting.
Doing structural calculations on the effect of Perry reflex shows that the benefits continue increasing well past the point where a bow made with Dan's original method (a straight belly pulled forward into reflex) would become pretty unruly due to all the unbraced reflex.
Also in TBB V3 was a section by Tim Baker on the DuoFlex bows. In it he suggested adding Perry reflex to the DuoFlex design by deflexing the belly lams during the initial splicing together of billets. This got me thinking about ways to increase Perry reflex without ending up with too much unbraced reflex.
Inspired by Tim Baker's thoughts, I ended up with the idea of making a multi-lam bow where the belly lams and core were initially glued into deflex and then pulled forward into reflex when gluing on the back lam. This way, the belly could have the preload effects of more reflexing, but the finished bow would only have moderate reflex that doesn't over stress the back and leaves it easier to tiller and brace.
My first design glues up the belly and core lams with the nocks having ~6" of deflex, then glues on the back with ~3.75" of reflex. Assuming some spring back off the form, I hope to end up with close to 7" of reflexing effect at the nocks, but only 2-3" of overall reflex.
Mark
For my first attempt at this I am using red oak boards for the wood. I like red oak for it's beautiful appearance, it is an OK bow wood and it is cheap enough that I can scrap a few without crying over the cost.
EDIT - The first bow design I am trying is a pyramid back profile, 67" NTN, target weight of 40-42# @ 28".
This is a dry fit practice run for the first glue up. The core lam, risers and belly lams are clamped in place. The deflex and reflex shapes are in circular arcs. This is because the bow design has a pyramid back profile that will bend in an arc of circle tiller. For a back profile that gives an elliptical tiller you would want to do the deflex and reflex using elliptical arcs.
(https://i.imgur.com/bczuFTo.jpg)
The actual glue up:
(https://i.imgur.com/Au0P63b.jpg)
The bow off the form:
(https://i.imgur.com/ljBBMPx.jpg)
This attempt was a failure due to gluing problems. I used Titebond III because it is more than strong enough, is much cheaper than epoxy and has no toxic fumes. Being water based, it caused the lams to cup heavily, resulting in large gaps on the edges of the lams.
(https://i.imgur.com/lOro44t.jpg)
(https://i.imgur.com/xTgiVjn.jpg)
It wasn't all a lost cause, though. I learned that the bow kept a bit over 5" of the 6" of reflex that the form has. That is better than I expected. I also got to experiment with bending the bow limbs forward into the 3.75" of reflex I planned for gluing the back lam on. They will easily bend that far with minimal effort, so I know that the second glue up will not cause problems in that way.
I also had problems with getting the belly lams to form to the ramps on the risers due to their thickness. I boiled them and clamped them onto the riser to pre-bend them to the ramp radius, but there was lots of spring back and they still needed a lot of clamping force to get them tight to the ramps and the fades off the riser. I also had issues with feathering the fades out to zero thickness, but that was due to my inexperience with making a riser block and nothing to do with the Perry reflex part of the experiment.
The lam thickness I tried is one of those places where a lack of experience with this design is hurting me. For a same wood bow (with all lams from the same wood), Dan Perry recommended having the belly lam be 2/3 of the thickness and the back lam 1/3. So that is the ratio I was using on the first attempt. That is what resulted in the 0.150" belly lam that didn't want to bend up the riser ramps easily.
Since I started, I have done more analysis on the effects of Perry reflex and it turns out that the effect is increased with thinner belly and back lams. This means Dan's recommended 2/3 belly - 1/3 back ratio isn't that important and I can go thinner to make it easier to bend them onto the form. The downside that I can see (so far) is that the thinner lams won't hold the deflex and reflex shapes off the form as well. This can be compensated for by increasing the amounts on the form, but it is not something that is easy to calculate and I am going to have to make a few bows to see how much extra is needed.
Mark
Maybe you should give unibond800 a try.
I get a gallon delivered for about $35.00
After my difficulties of forming the belly lams up the riser ramps I have been rethinking my riser design. Instead of the shape used in the first attempt, I am thinking of a multi-part riser similar to many FHLB designs use. In the picture below the original riser is on the right, an alternative is shown on the left.
(https://i.imgur.com/ujCIWTo.jpg)
The first riser ramps had a radius of just over 6.25". The second riser has bends of 10.375" radius.
Mark
How long is this bow going to be Nock to Nock? EDIT
67"
Quote from: Roy from Pa on January 22, 2021, 01:32:47 PM
Maybe you should give unibond800 a try.
I get a gallon delivered for about $35.00
It's still water based, though, isn't it? I think the problem is water being combined with wide, thin lams. I am thinking I am going to try another run with the TBIII and use aluminum pressure strips to keep the lams flat. If that doesn't work out then I think I will be stuck with epoxy.
I can't easily find the Unibond 800 up here, but I can find the DAP Weldwood equivalent. Any experiences with it?
Quote from: Mad Max on January 22, 2021, 02:09:40 PM
How long is this bow going to be Nock to Nock? EDIT
67"
Good point. I edited my third post to include the bow specs for the first design.
Mark
Biggest problem I see is those pinche' clamps. A bunch of 2" C-clamps would work better, barring a more effective setup. Those spring clamps aren't for glue-ups, which I am sure you know. It looks like you are not using a pressure strip on both sides? How are the clamping pressures distributed? I know in a different thread, you said you calculated the fade length, but it looks like they still ramp up too fast from the feathered edge. Obviously that would be eliminated with a different design
Also, there is no reason you can't thin out the lams as they go up the ramps. It would make that bend easier to achieve, if you ever decide to try this design again.
There could be other issues, those are just the one that are obvious from your pictures.
Quote from: Flem on January 22, 2021, 02:54:45 PM
Biggest problem I see is those pinche' clamps. A bunch of 2" C-clamps would work better, barring a more effective setup. Those spring clamps aren't for glue-ups, which I am sure you know. It looks like you are not using a pressure strip on both sides?
The spring clamps were used when I ran out of the F clamps. Definitely not my first choice. I went out and bought a dozen 3" C-clamps the other day to solve that problem. I was not using pressure strips on that one but I will be on the next one.
Quote from: Flem on January 22, 2021, 02:54:45 PMAlso, there is no reason you can't thin out the lams as they go up the ramps. It would make that bend easier to achieve, if you ever decide to try this design again.
Yes it would. I thought of that but had no good way to taper them. Next time I go this route I will use thinner lams and maybe add a taper as well.
Mark
Unibond800 has a low water content.
Quote from: Roy from Pa on January 23, 2021, 09:46:32 AM
Unibond800 has a low water content.
That would be helpful. I will have to see if I can find any up here. Where do you order yours from?
Mark
Check your PM
I would make sure the sun is not shining on the bow while it is drying.
(https://i.imgur.com/wCXv3i1.jpg)
That's what the piece of plywood behind the bow is for, he was taken pichers first..
Quote from: Mad Max on January 23, 2021, 03:35:26 PM
I would make sure the sun is not shining on the bow while it is drying.
There's something I never thought of. The sun has so little energy up here at this time of year it doesn't warm things up much, but I will keep that in mind for when things get hotter towards summer.
Quote from: Roy from Pa on January 23, 2021, 04:16:30 PM
That's what the piece of plywood behind the bow is for, he was taken pichers first..
I wish I was that far ahead of things...
Mark
:thumbsup:
I've built a number of wood bows "like glass bows" as you asked in your previous post, and I've dealt with some of the problems you're taking about.
Titebond will swell the wood and the back and belly laminations will cup. To counteract this I've had success using a lot of clamps and only putting them on the edges of the limbs. Also, titebond adds a lot of water to the bow, so I would let it sit on the form for a week, then let it dry for another 3weeks or so. Trust me, it seems dry but it's not. For these reasons I started using EA-40 epoxy. I did not bake it. Let it cure at room temp for 2days on the form. Had only one failure with EA-40 and it was in a bow I traded so I didn't inspect after. I suspect the power lam was too thin. Sorry woodcarver, I still feel terrible about that.
[attachment=2]
Regarding the riser fades, I ran the core and belly lam through the riser so the fade was more gentle, others like woodcarver have had success running lams up the fades, but I think he thinks the lams at the fades to make the bend.
[attachment=1]
Also, much like woodcarver does, I pre-taper all three lams (I use hickory backing, various cores, and typically Ipe belly). They come off the form so close to final tiller that I round the corners and can typically go straight to low brace. Tillering is very quick, basically just a scraper and some sanding. As a result, the lams are well proportioned all the way to the tip. I taper each lam to .002"/inch. That seems to be about the sweet spot.
[attachment=3]
I don't pre-deflex them. I just glue the lams up at once. One point I would note is that I think that perry reflexed Tri-lam bows take more set than a self bow, so you need to start with more reflex than you might otherwise. Maybe I'm just doing it wrong though and others may have different experiences.
[attachment=4]
Those 4 on the table are all wood? Nice :thumbsup:
Quote from: LittleBen on February 09, 2021, 09:18:04 PM
I've built a number of wood bows "like glass bows" as you asked in your previous post, and I've dealt with some of the problems you're taking about.
Thanks for the reply and the info on your experiences. Those are some beautiful bows, I hope to get mine looking that good at some point.
I think I am going to switch to epoxy or one of the urea glues before I am done. I still haven't figured out how to get everything glued up and clamped fast enough before the titebond starts to set and the lams are all cupped. I may try one more with titebond and pressure strips to see if I can keep it all straight, but I am not at all sure it is going to work out. If that doesn't go then it will be epoxy or urea glue next up.
I know what you mean about how wet the wood gets. My first glue up felt damp for days afterwards and our humidity is super low inside in the winter, so it is the best drying conditions possible.
Mark
Little Ben...
How the heck have you been?
Been a long time.
EA40 is a great glue for bows and so is unibond800 for wood bows.
Unibond800 has a very low water content and gives me plenty of time the get the bow clamped up, plenty of time, and it has never failed me..
I can get unibond800 for a couple bucks more than titebond 3.
I don't understand why some guys sacrifice building a bow with titebond 3 when for a little more $$ you can get an industrial strength glue?
I bought a pint kit of unibond and it was out of date, it was like a hard piece of Jello in the can.
Send it back.
Don't ya check the dates on stuff ya buy?
Quote from: Roy from Pa on February 10, 2021, 08:27:06 AM
Send it back.
Don't ya check the dates on stuff ya buy?
I could not see that far, online order :tongue:
Send it back.
Quote from: Mad Max on February 10, 2021, 08:13:55 AM
I bought a pint kit of unibond and it was out of date, it was like a hard piece of Jello in the can.
Yah just need a stouter putty knife to spread it... :thumbsup: :laughing:
Quote from: LittleBen on February 09, 2021, 09:18:04 PM
I've built a number of wood bows "like glass bows" as you asked in your previous post, and I've dealt with some of the problems you're taking about.
Titebond will swell the wood and the back and belly laminations will cup. To counteract this I've had success using a lot of clamps and only putting them on the edges of the limbs. Also, titebond adds a lot of water to the bow, so I would let it sit on the form for a week, then let it dry for another 3weeks or so. Trust me, it seems dry but it's not. For these reasons I started using EA-40 epoxy. I did not bake it. Let it cure at room temp for 2days on the form. Had only one failure with EA-40 and it was in a bow I traded so I didn't inspect after. I suspect the power lam was too thin. Sorry woodcarver, I still feel terrible about that.
[attachment=2,msg2951568]
Regarding the riser fades, I ran the core and belly lam through the riser so the fade was more gentle, others like woodcarver have had success running lams up the fades, but I think he thinks the lams at the fades to make the bend.
[attachment=1,msg2951568]
Also, much like woodcarver does, I pre-taper all three lams (I use hickory backing, various cores, and typically Ipe belly). They come off the form so close to final tiller that I round the corners and can typically go straight to low brace. Tillering is very quick, basically just a scraper and some sanding. As a result, the lams are well proportioned all the way to the tip. I taper each lam to .002"/inch. That seems to be about the sweet spot.
[attachment=3,msg2951568]
I don't pre-deflex them. I just glue the lams up at once. One point I would note is that I think that perry reflexed Tri-lam bows take more set than a self bow, so you need to start with more reflex than you might otherwise. Maybe I'm just doing it wrong though and others may have different experiences.
[attachment=4,msg2951568]
Ben!! Where you been?? Missed your building adventures in the tiny apartment. :)
BTW, this is Monterey.
Been doing the parenting thing (1yo, 3yo, and 5yo), and the homeowner thing (80yo house), so time has been at a premium. Been making more furniture than bows, although I'm chipping away at a few. I lurk on here from time to time, but don't usually comment at all. I just thought I would jump in on this thread because it was close to the process I've been using for my bows.
Glad to see a lot of the usual suspects still around. Hoping to stay a little more involved, just don't expect any build alongs anytime soon.
To the OP, you can always PM or post if you have specific questions on specs and so on.
Quote from: Roy from Pa on February 10, 2021, 04:11:52 AM
I don't understand why some guys sacrifice building a bow with titebond 3 when for a little more $$ you can get an industrial strength glue?
The problem is I can't get unibond for a bit more than TBIII, it is more like 3x the price up here if I mail order from the US. Shipping of a 1/2 gallon kit is $55 up to here from the place you sent me the link for. By the time I pay that and the exchange rate it will be ~$120 for that 1/2 gallon. I can buy a quart of TBIII for ~$25.
Quote from: LittleBen on February 10, 2021, 01:53:04 PM
To the OP, you can always PM or post if you have specific questions on specs and so on.
I do have a question that I forgot to ask in my last reply. How thick are you making your lams, especially the ipe belly lam?
Mark
I've never had a failure using tb3. I only use fresh glue.if it's getting old, I save it for non stressed glue ups.
As far as set up time is concerned, the first couple of times were a bit hectic, but then I started to get really organized before I started gluing. All the clamps ready and close to hand. A wet rag for wiping up drips etc.
Dave.
Quote from: wood carver 2 on February 10, 2021, 04:42:24 PM
I've never had a failure using tb3.
I have never had issues with TBIII or plain old yellow carpenter's glue on a bow so far. If the joint is done properly it is stronger than the wood. My only issues were the set up time and the water content causing the lams to warp. If I can streamline the glue up so that it is all together quickly lots of clamps and pressure strips will hopefully solve the warping problem.
Quote from: wood carver 2 on February 10, 2021, 04:42:24 PMAs far as set up time is concerned, the first couple of times were a bit hectic, but then I started to get really organized before I started gluing.
Hectic is a good word. I was pretty organized, but not nearly good enough for the time I had. My next try is going to be with the alternative riser design I posted above, which should be much faster to get assembled once the clock is ticking on the glue.
Mark
X2 what Dave said. Never had TB3 fail, and you get used to the glue up and it goes quickly.
I made my lams .150" thick and that would get me in the roughly 45# range (IIRC) at 28" on a 66" bow 1.5" wide with 12" riser. That's with hickory back, hickory core, and ipe belly. But that's also with black ipe, that's extremely dense. Obviously the design you use, as well as the materials will change all that. Also small changes in stack thickness can cause large be increase in weight.
I have two of the same design both 12" riser 66" one .420 stack is 34-35#, .480 stack is nearly 50#
Another 18" riser 66" bow .420 stack is ~45#.
So you can see small changes can be huge.
I dealt with this by making numerous of the same design and only changing the stack slightly, or the length slightly and so on, then used the data to create a chart to give some idea where I needed to be with the stack. Also I would err on the lighter side because a too light bow can always find a home, but no one really wants the 68# mistake.
I don't think I have the chart anymore, but also it only really works if you have the same belly, core and backing material. I cut lots of lams from the same boards so that everything was as consistent as possible. If I changed belly material, I would just make a guess about how that would effect weight.. In general, denser belly wood will increase draw weight, so you could guess that you might gain or lose a couple pounds going from one ipe board to another ipe board based on density. But going from ipe to yew, or Osage? Forget making any kind of accurate guess.
Is all this worth it? Maybe not. I did it because I had a lot of time, and it was cheap. And also I'm way better at engineering than I am at tillering, so it made sense for me. You could leave extra thickness on the belly lam, and tiller to target weight, but that's just not how I personally chose to do it.
Quote from: LittleBen on February 10, 2021, 05:35:44 PM
I made my lams .150" thick and that would get me in the roughly 45# range (IIRC) at 28" on a 66" bow 1.5" wide with 12" riser.
I'm impressed that you got lams that thick to make the bends, especially in ipe.
Quote from: LittleBen on February 10, 2021, 05:35:44 PMAnd also I'm way better at engineering than I am at tillering, so it made sense for me.
That makes two of us. I design my bows using software and it works out better than my shaky eye on a tillering tree starting from a raw stave. With wood there will always be a bit of refinement required, but it can be very minimal if the design and fabrication is done well.
Mark
QuoteThe problem is I can't get unibond for a bit more than TBIII, it is more like 3x the price up here if I mail order from the US. Shipping of a 1/2 gallon kit is $55 up to here from the place you sent me the link for. By the time I pay that and the exchange rate it will be ~$120 for that 1/2 gallon. I can buy a quart of TBIII for ~$25.
Well that explains that...
the titebond found at retail outlets is a smaller selection of a more extensive product line mfg by franklin.
lots of data on recommended practice etc.
http://www.franklinadhesivesandpolymers.com/Wood-Adhesives-US/Wood-Adhesives.aspx
of interest to bowyers might be extended set time formulas in the titebond product line or wood mc recommendations for longer working times.
Those are really nice littleben :thumbsup: :jumper:
Thanks MadMax
Quote from: LittleBen on February 11, 2021, 09:42:19 PM
Thanks MadMax
This could be my new calling :thumbsup:
I've made 3/4 Boo back bows but I would have more control with the lams and Hickory back.
What other backings do you use? Maple?
Do you have a full draw picture?
The tiller looks very good. I'm assuming this is all red oak, back, core and belly, is that right? Red oak is a marginal bow wood and especially as a belly wood. This could be why it took some set. Also, I think you may have over stressed the red oak at each stage of the glue up. Again, that being said, it is a well tillered bow. How does it shoot?
Quote from: Pat B on December 03, 2021, 09:36:18 AM
The tiller looks very good. I'm assuming this is all red oak, back, core and belly, is that right? Red oak is a marginal bow wood and especially as a belly wood. This could be why it took some set. Also, I think you may have over stressed the red oak at each stage of the glue up. Again, that being said, it is a well tillered bow. How does it shoot?
Pat I think you are on the wrong perry reflex topic, this is a older one
That comes with age. :thumbsup: