To back or not to back…or where to back?

[Capt.Moses]

I’ve recently taken it upon myself to make a recurve/Holmegaard style bow. The Holmegaard bow has very wide lower limbs that taper off quickly into thinner upper limbs, which act as levers to put more power into the lower limbs. I thought that by making them recurved, it would only enhance their levering abilities, making for a faster bow. I linked an image of the design below(without the recurve modifications). If I decide to put a linen backing on the bow, do I put it on the recurved section as well as the normal part of the bow, or only the normal flat part? Also, I haven’t yet found a definitive answer as to why fiberglass/drywall tape is a bad backing other than “it’s not natural” and “it’s ugly”. I’m sticking to linen for this build, but might try out some other types later down the road, and want to know which ones I can skip. Thanks!

[sleek]

Recurves don't exactly increase leverage, they more keep the string angle constant through the draw. Which is why longer bows don't benefit from recurves.

It's one way to look at it that they increase leverage on short bows, but thats not universal to all bows. What is universal is them keeping the string angle down. So that's the way I prefer to have it explained.

Now I know that's not the question you asked, but I hope you see that with that information, recurring won't help you unless your draw exceeds what the bows length allows.

[willie]

welcome capt

a backing would be for the working inner limbs, as the lever would not be bending much and be stressed less

just curious of the purpose for linen backing, and how thick are you thinking the linen will be?

this is a curious design and hope you can link to a pic showing the proposed reflexed tips
significant reflex in the outers will most likely call for thinner and wider inners than a straight bow of same poundage

[sleek]

Fiberglass tape, as typically applied, adds no strength to the back. The adhesive doesn't bond to the wood well enough to reduce the strain on the back. So it's only purpose would be a shrapnel net should the bow self identify as a grenade.

If you were to apply the glass in an effective manner by removing the adhesive and laying it with epoxy, the glass would make a fantastic backing. One so good infact, that the wood would make a terrible belly. The glass will likely overpower the wood and cause belly failure, aka, set.

That being said, your planed route is acceptable. Where to put it? On the working limb of the bow is the most effective area, passing by it an inch or so to give good attachment points for the backing to non bending wood. But, backings are not a magical solution to problems, sometimes not even needed. So I guess my next question is, why do you want to back it? Backing is kind of a pain.

[Capt.Moses]

Sleek,

Thank you for the advice about the fiberglass backing. I put one on my first bow I made with wood glue, and it seems to be the only thing holding it together, so I will take that into account for future builds. As for the current build, I’m making it with a hardware store plank. I don’t feel entirely confident that it’ll be able to withstand significant pressure, so I figured I’d use it to try out a new backing method(new to me at least).

[Capt.Moses]

just curious of the purpose for linen backing, and how thick are you thinking the linen will be?

this is a curious design and hope you can link to a pic showing the proposed reflexed tips

I saw a method that used 10 or so lengths of linen twine spaced out across the back of the bow(not sure if this is usual or traditional but I’m just going with it). As for the proposed recurve tips, I only have a very rough sketch to show you. The thin part of the bow is roughly 15 inches long(according to the plans in the original post), and I plan on making it so about 3 inches is perpendicular to the bow, with about 6 inches or so for the curve.

[lebhuntfish]

Backing is a good safety net especially for new bowyers.

I remember when I started, I got caught up with all the different ways people had made bows, and all the different backings.
I will tell you this, throw away your FG tap! If you do some research it's been proven as pretty much a waste of time and money.
Now, our ancestors had it figured out they didn't know it but they just used what they had available.
If you want a extremely strong backing that is fairly easy to apply then get you some rawhide. Don't use the dog bone rawhide like on YouTube. Use thin deer rawhide or I use thin goat rawhide because I can find it easily and the price is a little better. Then mix you up some hide glue with Knox unflavored gelatin.
Apply the glue to the bow and the rawhide and just glue it down and work all the bubbles and extra glue out. Work it for a few minutes until it starts to set then let it dry for a day or so. Use a rasp to clean up the edges and light sanding. That's about the strongest backing you can get. Except sinew, but that's a more advanced process.

Patrick

[GlisGlis]

that has been discussed many times but holmegaard bow do not show any real sign of having levers (stiff section)
These are the true holmegaard dimensions





Your reference could be the mollegabet bow that has a bending section followed by a thin rigid lever.

[superdav95]

Agreed. It does sound more like he is describing mollegabet style bow.  I’ve done a number of these and have incorporated a slight bend in the levers and they are non bending so no sinew or backing used on the levers.  I used a thread wrap where the backing ended at start of levers.  I’ll try and dig up some pictures.   

[willie]

I saw a method that used 10 or so lengths of linen twine..............

If the twine will be for safety against breakage and you are building with a board, my thoughts are the proposed width profile/crossection combined with the proposed recurve tips will result in a lower poundage bow once tillered out.

If you wish to optomize the board for the best bow possible, and are open to suggestions, could you post how long/wide'thick your board is and how many pounds pull and draw length you are looking for?
maybe mention something about the previous bows you have built?

[sleek]

If I weren't already making bows your work here would certainly get me started! I want to learn more about this one. got a link to it?

Agreed. It does sound more like he is describing mollegabet style bow.  I’ve done a number of these and have incorporated a slight bend in the levers and they are non bending so no sinew or backing used on the levers.  I used a thread wrap where the backing ended at start of levers.  I’ll try and dig up some pictures.   

[Capt.Moses]

If the twine will be for safety against breakage and you are building with a board, my thoughts are the proposed width profile/crossection combined with the proposed recurve tips will result in a lower poundage bow once tillered out.

If you wish to optomize the board for the best bow possible, and are open to suggestions, could you post how long/wide'thick your board is and how many pounds pull and draw length you are looking for?
maybe mention something about the previous bows you have built?

The board I’ll start with will probably end up being roughly 2.5 inches by 1 inch(might shoot for 1.5 to be safe), and about 66” long(before I recurve the ends). As for poundage, I’m looking to make it 35-40 lbs at 24”, although I don’t have a reliable set up to test that quite yet.

[TimBo]

Hey Sleek, I think it's this 'un.

http://www.primitivearcher.com/smf/index.php/topic,71608.msg1003927.html#msg1003927

[JW_Halverson]

If the twine will be for safety against breakage and you are building with a board, my thoughts are the proposed width profile/crossection combined with the proposed recurve tips will result in a lower poundage bow once tillered out.

If you wish to optimize the board for the best bow possible, and are open to suggestions, could you post how long/wide't (-_)hick your board is and how many pounds pull and draw length you are looking for?
maybe mention something about the previous bows you have built?

The board I’ll start with will probably end up being roughly 2.5 inches by 1 inch (might shoot for 1.5 to be safe), and about 66” long (before I recurve the ends). As for poundage, I’m looking to make it 35-40 lbs at 24”, although I don’t have a reliable set up to test that quite yet.

If you are talking board bows, they I have to recommend my friend Weylin Olive's YouTube series on building a board bow. He breaks it down DEEPLY and still keeps it moving along and interesting. The very first one of the series is about how to choose the board. If you follow his instructions, then you have eliminated 90% of all the problems you could run across while making the bow....including eliminating the need to back the bow. A well-chosen board needs no backing, ever.

At the low draw weight you are looking for backing is definitely not necessary because draw weights like that are not a great strain on the wood.

"I put one on my first bow I made with wood glue, and it seems to be the only thing holding it together".  How do you know that is what is holding it together? Has it had a catastrophic hinge and failed? That is the only way I know of that you can test whether a backing is actually holding a bow together.

I want to put a challenge to you. Send me that bow, I will remove that backing and prove to you that the bow is still holding together. As an admin on a Facebook page dedicated to board bow building with 26,000 members, I have seen dozens and dozens of these bows backed with this material....and they fail just as often, if not more often, then unbacked bows. ALWAYS, with EVERY bow, no matter the hundreds of choices you will make in the process, the first step will forever be your choosing the piece of wood. Pick the right grain, only the right grain will do.

If you do not choose wisely, every subsequent choice is only mitigating the degree of failure. I hope this is not coming off as harsh, but I have to rush to get this done and get my butt out the door. I don't mean to discourage, in fact, just the opposite because I really want to see this bow you are describing. It sounds like it would be elegant, graceful even. And if you play with bows for long, you will discover that good shooting bows are always elegant!

[superdav95]

If I weren't already making bows your work here would certainly get me started! I want to learn more about this one. got a link to it?

Agreed. It does sound more like he is describing mollegabet style bow.  I’ve done a number of these and have incorporated a slight bend in the levers and they are non bending so no sinew or backing used on the levers.  I used a thread wrap where the backing ended at start of levers.  I’ll try and dig up some pictures.   

Thanks Sleek!  very kind of you.  it was a fun and interesting build.