Red oak riser question

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Forester
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Red oak riser question

#1 Post by Forester » Sun Jul 24, 2016 7:52 pm

Hi folks, I have a question that I am hoping to get some feedback on from the seasoned bowyers out there.

I have started a red oak board bow and have shaped it out and glued on the riser, but after chatting to Perry at the Jules Trad Shoot it seems I have made a big mistake. My board is only about 16 mm thick, which does not allow for the fades to extend into the actual limb wood. As I had read on here that a starting limb thickness of around 15 mm would be ok, I didn't think I needed a thicker board. Apparently this set up will inevitably lead to the riser popping off, and after looking up that issue on Ozbow and other sites, I can see that I should have done several things differently (several thinner riser laminations, longer fades and extending the fades into the limb thickness).

The question I have now though, is what I can do to salvage it? I have not invested a massive amount of time on it to date but am still reluctant to have to abandon it or have it break on me. I have attached a few photos, and these are the vital stats: I am aiming for 45 – 50#, with Length – 68” ntn; Handle 4”; Fades 3”; Width – 2’’ at the fades, parallel for the next 2”, then straight lines to ½ “ nocks. Thickness is uniform currently at about 16 mm and with no thickness tapering at all yet it draws about 20# at 7 inches.

My feeling at the moment is that I should keep the riser as stiff as I can and try and tiller it such that the near-handle wood does not bend at all, so that no stress is put on the riser join. Or, would it be better to make the riser very thin so it bends easily…? One thought I had was to wrap the handle in glue soaked twine as a handle wrap and also popping off insurance – and also to wrap the last half inch of both ends of the riser in the same way too keep them from lifting up – sound fair?
Any thoughts or advice would be greatly appreciated!
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red oak front view.jpg
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cadet
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Re: Red oak riser question

#2 Post by cadet » Sun Jul 24, 2016 9:44 pm

I'm no expert, and the stiff-handled, wide-limbed pyramid-ish bows aren't my thing, but I'd agree with working the fades into the actual board, well beyond the handle, and tillering to keep all of that handle area stiff. You may not get the weight you're after, but I'd be less concerned with that than just getting a well-enough tillered, working bow.

Sabinus
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Re: Red oak riser question

#3 Post by Sabinus » Mon Jul 25, 2016 7:17 pm

Hey Forester,

Look at many pyramid bow buildalongs and if there is a rule of thumb regarding limb thickness @2inches wide, it is to get your limbs to just over 1/2 inch thickness for their full length. Thinking of the limbs being around 13 or so millimeters thick, that gives you 3 mm of extra fade down into the working limbs. If you filed your fades into a very gentle, concave curve down to 13mm thickness, your riser block may yet be protected from popping off. my $.02.

Note - the limb thickness is a guide only. The density of your piece of red oak will have a big say in the draw weight, but I would have thought you'd be on track for 45-50# @28inches with limbs of your listed width and length. Obviously take Perry's advice as he knows what he's talking about! I've found myself trying to wrench a result of some sort from initial errors before too though - time is precious so I know it's not easy to shrug and scrap a bow that just may have some life and some lessons left in it!

As a last note (I promise!:)) Yeoman would be the man here with current data and experience regarding red oak pyramid bows.

Best of luck

hunterguy1991
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Re: Red oak riser question

#4 Post by hunterguy1991 » Mon Jul 25, 2016 7:38 pm

Few cents on the issues from my experiences.

Is that 20lb at 7" from straight or from brace? If its from brace then that bow will be over your desired weight (provided an ideal world, 20lb at 7" with a 7" brace would mean a 21" draw and a linear curve would predict about 60lbs at 28")... if that's from straight then you have a tonne of wood to play with.

The trick with fades is to get them as shallow as you possibly can... the term feathering is used with making glass lam bows and you can dam near see through the fades of the riser block. To get your fades to work you need to make them a concave curve as Sabinus suggested and very fine at the merge of the handle block to the limb board. I would think that at 16mm you have a few mm of wood to play with tho and should be able to get enough bend in the fades for them to stay on... tho that will also depend on what you glued the block on with as well...

As Cadet said, be more concerned with producing a shooting bow first and learn from the little intricacies in the process and apply them to the next one.

Colin

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Forester
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Re: Red oak riser question

#5 Post by Forester » Mon Jul 25, 2016 8:52 pm

Thanks very much for the input fellas.

That 20# at 7 inches is from straight, so it is good to hear that it seems like I do have some thickness to play with yet ("a tonne of wood" sounds very encouraging, Colin!) I have not used red oak before, but perhaps this means I also have a moderately dense piece (fingers crossed).

I will do as you all suggest and shape those fades concave (they have only been roughly shaped until now) and try and extend them into the limb as much as I can. Hopefully I have got the 3 mm you mentioned Sabinus, and praps a bit more. As you say Cadet, I will try not to get too ambitious and if it ends up a little lighter than intended, so be it.

One thing I am a little confused about though is whether to get the fades working or not. Although I understand the performance benefits of getting the bow bending close to the grip, I thought the cause of risers popping off was partly because of the (glued on) fades bending, and therefore to keep them safe I imagined that they should be kept stiff, as well as the nearest part of the working limb. Can anyone comment on this?

Thanks again for the advice and I will keep you posted as to how it goes.
Last edited by Forester on Mon Jul 25, 2016 9:46 pm, edited 1 time in total.

hunterguy1991
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Re: Red oak riser question

#6 Post by hunterguy1991 » Mon Jul 25, 2016 9:45 pm

The purpose of the fades is to gradually stop the bend from the limb into the handle rather than abruptly stop it (creating a hinge) so the very fine end of the fade will bend a tiny bit but stop as it thickens into the handle.

What you have will make a bow of around 45-50lbs at those dimensions I believe but again, don't be too concerned with the weight, just get a shooter! :wink:

The reason risers "Pop" off is because the shear stress is too great because of the bending load placed on the handle. Even if a handle does not actually bend, it is still subject to bending load and hence, bending stress. When a handle is glued on it essentially becomes a single piece of wood HOWEVER as the timber is loaded it induces shear stress as well as bending stress... when these shear stresses are more than what the glue can hold... POP... (that's the simple version of whats going on anyway)

hope that helps,

Keen to see how the bow turns out so keep us posted!

Colin

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Forester
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Re: Red oak riser question

#7 Post by Forester » Mon Jul 25, 2016 9:55 pm

Great explanation, thanks Colin. What I hadn't appreciated before was the two different kinds of stress - I was only thinking of bending stress and it didn't occur to me that shearing stress would be at work even with absolutely no bend in the handle.

I will make those fades as smooth as I can and will dip down into the limb wood a bit too - so with a bit of luck that will do it. I used construction strength pva glue that is supposed to be stronger than hardwood, so hopefully that will hold...

I'll keep you posted!

hunterguy1991
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Re: Red oak riser question

#8 Post by hunterguy1991 » Mon Jul 25, 2016 10:13 pm

Will be interesting to see if that glue holds up. Ive never had any luck with anything but Techni-glue which is a structural grade epoxy.

Remember that even when a riser isn't "bending" there is still bending stress there, there is just no deflection (actual visible bend)

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perry
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Re: Red oak riser question

#9 Post by perry » Mon Jul 25, 2016 10:39 pm

Evening Forester, it was a pleasure to meet you the other Weekend.

You have been given some excellent advice by the Lads here, a better command of the Language than me.

You will get a working Bow no worries. After looking at those Pictures, the amount of Wood you have, the length of the Fades, Angles etc I really think you will get a lower draw weight than desired. Your Fades will be a little stiff I fear. They are just that tad short to taper/ feather correctly into the Limb as you say due to the thickness of the Board. When finished Fadeouts on this type of Bow are generally a bit longer, 4" is not too long and quite concave in profile. I have seen similar Bow designs with 5" Fades.

Binding will hold the Riser Block in place if the Glue Lines give out but the Bow will creak, groan and carry on like they do in Hollywood Films.

The only Focus at this point is to tiller the Bow to what it wants to be not what you want it to be. Staves tell you long in advance whats emerging. Observe the little signs, listen to it and you will be fine. I gotta wonder if this Stave becomes a Bow you may feel the tinniest bit of movement through the Grip. Maybe just maybe it will want the Riser section thinned down and rounded off to ease the strain on the Fades ????????????

regards Perry
"To my deep morticication my father once said to me, 'You care for nothing but shooting, dogs and rat catching, and you will be a disgrace to yourself and all your family.' "

- Charles Darwin

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Forester
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Re: Red oak riser question

#10 Post by Forester » Tue Jul 26, 2016 8:00 pm

Hi there Perry, it was good to meet you as well and put a face to the many posts of yours that I have read!

Thanks also for your input, I like your approach of seeing what best suits the piece of wood, rather than forcing pre-formed ideas onto a potentially unsuitable stave - a sure recipe for disaster. I just hope I can read its signals correctly...! I am going to lower and round off the handle, try to feather the fades as best I can and hope for the best.

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perry
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Re: Red oak riser question

#11 Post by perry » Tue Jul 26, 2016 10:21 pm

beware of preconceptions Forrester and let the stave evolve. Your working with the stave, we have only looked at pictures.
"To my deep morticication my father once said to me, 'You care for nothing but shooting, dogs and rat catching, and you will be a disgrace to yourself and all your family.' "

- Charles Darwin

RobHunter
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Re: Red oak riser question

#12 Post by RobHunter » Wed Jul 27, 2016 8:15 am

Guys

Wouldn't an overlay on the back, extending beyond the riser, reduce the bend and therefore the stress?

Rob

hunterguy1991
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Re: Red oak riser question

#13 Post by hunterguy1991 » Wed Jul 27, 2016 6:16 pm

Stress is related to load not amount of bend... Stiffening the handle will reduce the strain on the handle but not the stress. Stress on the outer most fibres of a beam is determined by dividing the bending load multiplied by the distance from the neutral layer to the fibre all divided by the second moment of inertia of the beam cross section.

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Forester
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Re: Red oak riser question

#14 Post by Forester » Wed Jul 27, 2016 8:45 pm

I'm glad you raised that point Rob, as I have recently came across a few posts on other forums that said the same thing for a similar problem and I was wondering if that would work here.

Colin - back to what you were saying before about it being shear stresses and not bend that makes handles pop off - surely at some point (of thickness of handle for example) shear stress would not be present? I thought that a bow's limbs took the strain as they bent (if tillered correctly), and if near handle wood was left thick, it shifted that stress further towards the tips. If making the handle and near tip wood immobile (for example by adding the wood to the back) does not reduce handle popping shear stress, what does? Everyone says that the feathering of the fades is important, and I intuitively understand the need for a gradual introduction of bend, but I don't understand how that reduces shear stress. If it does, it is presumably because it induces some bend - so therefore would the logical thing to do be to make the riser more flexible in an iffy situation like mine?

Sorry if I am being dense or missing something obvious - I fully respect your knowledge in this area and I am just trying to wrap my head around all this!

hunterguy1991
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Re: Red oak riser question

#15 Post by hunterguy1991 » Thu Jul 28, 2016 9:26 am

The only time there is any section of a bow that is not under some form of stress is when the bow is un braced (and even that depends on how the bow was glued up, ie adding reflex on a belly by adding a backing places stress on the bow even when its unstrung). As soon as there is load on the bow from bending there is stress all through the length of the bow, the magnitude and distribution changes of this stress changes as the bow is drawn. The only way to reduce the shear stress at the handle is to reduce the load on the handle ie, make the bow lighter so these shearing stresses are less than what the glue can withstand.

There is some very complex engineering at work in making a bow and some safety needs to be built into them to ensure longevity is maintained. This is why some of the bowmakers on this forum use guides like 2.5x draw length as their ntn length... It is for safety and longevity. Some timbers provide exceptions to these rules, like Yew and Osage...

hope that helps, and again, keep us posted on how the bow is going!

Colin

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