Blackbutt/How not to make a Static Recurve/First BBB

[Nezwin]

I recently decided to start on a bow based off of a profile I read of in an old English book on archery (The Book of the Bow, Gordon Grimley, 1958). Despite being overtly racist in place, it's not a bad little read.

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The bow was also to be my first real attempt at a Bamboo Backed Bow (hereafter referred to as BBB, because I'm lazy), having previously only backed with Fibreglass or cloth (or not backed, as per selfbows). To make sure I really broke with the scientific method and changed as many things as I could at one time, it was also to be my first time using Blackbutt as a compression timber. I had read elsewhere on these forums that it was a usable timber and it marked a change from the usual Ironbark or Spotted Gum I tend to use.

Being a BBB, I'd read that that these tend to take a lot of set & it was advisable to make recurved tips static to minimise this. The final stack ended up,

Pole bamboo (back)
Reconstituted bamboo (core), 0.002 taper
Red Gum tip wedges/3" powerlam (wedges to ensure static recurved tips, powerlam to shift point of bending away from the glued on riser)
Blackbutt belly, 0.001 taper (belly)

I glued up with Titebond III, first time I've used this since I lived in Canada. I had great success with it there and it makes for a great alternative to the more expensive epoxies. I used an adjustable-style form, using the natural bend of the grass/timber stack to dictate the precise Reflex/Deflex profile. The gluelines came out great and after trimming the profile I cleaned up the edges.

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After gluing on a beauty of a red gum/spotted gum riser (I really do like this combination),

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I thought I'd give it a quick floor tiller, just to see how it might bend. I thought only a couple of inches wouldn't do it too much harm.

Cue the compression crack at the wedge tip (ie, where the tip wedge ends).

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I had had my concerns about these wedges after trimming the profile and seeing the gap in the glueline.

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It was here that the belly cracked, which is no surprise really. Lesson learned - those wedges have to be really smooth in transition. Or Blackbutt isn't all that great a timber in compression??

Some time wasted, but a few lesson learned. I started on a second BBB today with the lams currently gluing up end to end, ready for the full glue up when I next have a few hours to myself. I'll be using a powerlam with this one too (I've had success in the past with these) but will be avoiding tip wedges, for now. Or maybe I will give them a shot, I have some 1/16th thickness red gum that might be better suited for that.

Reflections

- Don't try too many new things at once, the scientific method exists for a reason.

- Don't be so sure about Blackbutt. Maybe.

- Pole Bamboo is great to work with and if you fail with it, it's far less stress than a failure with expensive fibreglass.

- Similarly, a failure using Titebond III is much easier to cope with than a failure with an expensive epoxy. Far, far fewer hypothetical tears.

- I should've put as much attention on my wedges as I did my powerlam, which came out great.

- Drum/Thickness Sanders make life very, very much easier than an improvised system. First time using it and I love it already.

[yeoman]

Can we have a picture of the whole thing? I struggle a bit to discern what we're seeing in the pictures posted.

My blackbutt bow is backed with just webbing. I think it might be too weak in compression to really be a match for bamboo, unless you trap the back.

Keep trying though.

[greybeard]

Can we have a picture of the whole thing? I struggle a bit to discern what we're seeing in the pictures posted.....

I agree with Dave, and do you have a clearer photo of the wedge glue line / failure.

Knowing the limb dimensions may help solve the cause of the failure.

I had had my concerns about these wedges after trimming the profile and seeing the gap in the glueline.....Similarly, a failure using Titebond III is much easier to cope with than a failure with an expensive epoxy. Far, far fewer hypothetical tears....

Most epoxies have good gap filling properties but we will never know if it would have prevented the failure. In a relatively simple glue up you may be looking at two to three dollars for the epoxy.

....Pole Bamboo is great to work with and if you fail with it, it's far less stress than a failure with expensive fibreglass......

That is if you don't factor in the lost hours profiling the pole bamboo.

On top of that you also have the all up cost of the failed project.

One other factor to consider; was the bow design suitable for the materials being used?

Daryl.

[Nezwin]

Can we have a picture of the whole thing? I struggle a bit to discern what we're seeing in the pictures posted.

I'm afraid I cut it up when I salvaged the riser. I still hadn't cut the fades to I took it off with the bandsaw & sanded down to the original shape.

I think it might be too weak in compression to really be a match for bamboo, unless you trap the back.

I've gone with the same lam combination with this next bow, keeping the same dimensions & profile to see how it compares without poorly made wedges.

Knowing the limb dimensions may help solve the cause of the failure.

The bow was 68" ntn to accommodate a 29" draw. The riser was 14" with a 20" powerlam (extending 3" past each fade) and 6" wedges at each tip leaving a working limb length of 21". Not too short, I thought.

The bamboo backing was approximately 1/4" at the crown (perhaps too thick, in retrospect) with 1/8" lams of compressed bamboo decking & Blackbutt, with 0.001' & 0.002' respective tapers.

The bow was 1.5" wide at the centre, extending parallel to the end of the powerlam, 10" from centre. From here I drew lines to the centre point of the tips and measured to where the width of this 'pyramid' was 0.5", which was 28.75" from centre (give or take). From there the profile followed a 0.5" wide parallel taper to the tips. This is the profile outlined in the book and seemed a little different to the usual flatbow profile.

Most epoxies have good gap filling properties but we will never know if it would have prevented the failure. In a relatively simple glue up you may be looking at two to three dollars for the epoxy.

Good point. Time to go the Smooth On route perhaps, or I might wait until I feel it's not my workmanship that not holding me back. This $30 bottle of TBIII should be used up by the time I get there. I guess it's good to find your feet with cheaper materials - saves wasting the good pile of Osage.

That is if you don't factor in the lost hours profiling the pole bamboo.

I actually found this to be pretty quick, compared to my previous method of making a homemade glass lam (which is fairly time & material intensive, but pretty rewarding in itself). From splitting the bamboo to finish maybe took an hour and a half and was more satisfying work than preparing resin & glass in a form. Having said that, I'm not sure I did it completely right either. I'll do a search for 'preparing pole bamboo'.

One other factor to consider; was the bow design suitable for the materials being used?

No idea but it does look like the Blackbutt is not up to compressing the bamboo. I've already prepped the lams for a second, following the same profile & materials as the previous only without the tip wedges. I'll post the results.

Thanks for the input though, I'm sure the next one will come out far better.

[greybeard]

..........The riser was 14" with a 20" powerlam (extending 3" past each fade).......

Did the bow design require a 'powerlam', there is no data available to prove their worth and only appear to complicate bow construction.

.........The bamboo backing was approximately 1/4" at the crown.......

If the bamboo backing was approximately 1/4" thick at the handle how thick was it at the tips?

Daryl.

[Nezwin]

Did the bow design require a 'powerlam', there is no data available to prove their worth and only appear to complicate bow construction.

The bow was to have a glued-on riser, so in order that the glue joint would be less stressed I put a powerlam in. The 3" section would still bend with the limb, but less so than it would without the additional limb depth.

Aside from two self-bows (Pacific Yew & a Himalayan bamboo) & a cloth backed board bow (fibreglass cloth backed spotted gum), all my bows have been variations on a lam stack. Even with tapered lams, I've found that the limb can bend a little too close to the riser joint than is comfortable. Running the belly lam up the fades ofcourse negates this but isn't the best design for an adjustable style form, requiring multiple glue ups (as per your Italian renaissance inspired BBB - http://www.ozbow.net/phpBB3/viewtopic.php?f=3&t=5341 -

Although I made a solid form for this bow only the core and belly were glued up on it. A moveable form was used to glue the backing bamboo.

- which happens to be a style I'm aiming for eventually). Getting the fades tapered correctly for a smooth lam transition from limb to riser is something I've only successfully done a couple of times and I've still got to work on, as per the tip wedges in the post above.

If the bamboo backing was approximately 1/4" thick at the handle how thick was it at the tips?

Just the right question - the bamboo was essentially a parallel lam, uniform crown thickness throughout the full length, as a glass lam would often be. After searching the term 'preparing pole bamboo' on the forum I came across one of Yeoman's threads from 2006 where he outlined how he flattens his bamboo. It would seem that, once the bamboo has been cut to profile, it is again flattened to a uniform edge thickness, thereby giving it a natural taper. So there's actually two flattening processes that occur - the first to create a flat surface on which to draw a limb profile, the second to take the limb to the uniform edge thickness throughout after the limb profile had been cut. Is this correct? As I said, this is my first time working pole bamboo, so it's all a bit new to me and it would seem I had skipped the second flattening/thinning/tapering process.

My original pictures weren't so great and I've not had a chance to get out to the shed to take another set, but I've added the following pictures with some edits to highlight what I was trying to show as my errors (or, what I believe to be my errors, at least).

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Tip Wedge f-up.jpg (83.06 KiB) Viewed 3144 times

[greybeard]

.....Just the right question - the bamboo was essentially a parallel lam, uniform crown thickness throughout the full length.....

Basically a parallel pole bamboo lamination will stuff every bow.

The following is from previous posts.

Constructing Laminated Bamboo Bows.

I am often asked ‘how wide do you make the limbs’ and ‘how wide is it at the tips’.

The following is an explanation of my approach to making bamboo back and bellied bows. No doubt there are other methods of constructing this style of bow, I followed my instincts and trial and error took over.

Once you understand the workings of the simple selfbow the design and construction of a bamboo bow is relatively easy.

Patience is essential if you want to end up with a quality bow, rushing in will only bring you grief.

Limb width is governed by the diameter of the bamboo pole i.e. the smaller the diameter the higher the crown. For a standard type of longbow three inch diameter poles are ok, use larger diameter poles if you have access to them.

Note that the larger diameter pole is usually cut from the bottom end of a longer pole and the nodes will have a closer spacing. Ideally poles with nodes that are spaced somewhere from 12 inches to 15 inches or more are preferable.

For a first attempt I would suggest building a long bow/flatbow.

When preparing core laminations for a long bow I have an overall width about 1 ¼” to 1 ½” by the required length. Make a template slightly oversize of the desired limb plan and this will make the marking out of components more accurate and will save you a lot of measuring. Draw the plan of the limb shape on a lamination and include a centre line down the length and one across at the half way mark. This lamination is placed face down on the form when gluing up. Using two core laminations allows you to end for end the laminations to help minimise weak spots although I prefer three laminations.

Split or saw your bamboo pole into suitable widths and start flattening the inner surface with whatever suitable tools you have available i.e. belt sander, electric planer, spoke shave etc. Mark the limb plan [slightly oversize] on the bamboo and cut to shape. Draw marks across the bamboo at six inch intervals and these will be used as checkpoints to control the thickness and taper. Continue flattening the inner surface until the edges of the bamboo is about 1/ 16” thick.

For ease of construction I use a rigid form to glue up the core laminations, riser and belly bamboo as multiple laminations need a platform to keep them in shape when glued and clamped. The rigid form will need about five inches of reflex built into it as most of this reflex will pull out during the tillering and shooting in process. Unlike a glass laminated bow that will hold its tiller from the first arrow the bamboo bow may take a hundred or more arrows before its tiller settles.
With a three lamination core I prefer to run two laminations on the back and one on the belly of the riser.

When the glue has cured I use the adjustable form to glue up the backing bamboo.

For backing a stave with pole bamboo the Dean Torges DVD Hunting the Osage Bow contains some excellent information.

When I have prepared the bamboo backing I put it on the tiller to see if there are any stiff spots.

....I've found that the limb can bend a little too close to the riser joint than is comfortable. Running the belly lam up the fades ofcourse negates this but isn't the best design for an adjustable style form, requiring multiple glue ups (as per your Italian renaissance inspired BBB - http://www.ozbow.net/phpBB3/viewtopic.php?f=3&t=5341 - ....

I added a correction to that post stating that the backing bamboo was glued on using an adjustable form [last glue up].

If pole bamboo is being used for the back and belly laminations quite often you can run parallel core laminations.

Daryl.

[Nezwin]

I managed to get a few hours in the shed this weekend and glued up the lams I'd ground the previous weekend. The limb stack has ended up -

Pole Bamboo Backing
Processed Bamboo Core (1/8", 0.002 taper)
Blackbutt Belly (3/16", 0.001 taper)
Nil Powerlam/Tip Wedges

I left the powerlam out this time as I felt that, with the overall 0.003 taper + the bamboo taper, the bow will most likely be somewhat whip-ended and I didn't want to exacerbate that with less bend toward the riser. Care will be needed that the riser joint isn't subjected to too much force, though.

Split or saw your bamboo pole into suitable widths and start flattening the inner surface with whatever suitable tools you have available i.e. belt sander, electric planer, spoke shave etc. Mark the limb plan [slightly oversize] on the bamboo and cut to shape. Draw marks across the bamboo at six inch intervals and these will be used as checkpoints to control the thickness and taper. Continue flattening the inner surface until the edges of the bamboo is about 1/ 16” thick.

I used this method and it was quite time intensive & precise, but rewarding. I've found that while my attempt was good, there are gaps in the glueline for the backing, a sign of my unfamiliarity with this method of preparation & room for improvement. Arguably, an epoxy would've filled these gaps (as opposed to the TBIII woodglue that I used) but it does highlight areas for improvement in my next build & where I need to focus my attention for next time. I found the beltsander to be good for quick removal of material but it also lead to some uneven results (edge to edge), so next time I'll see how well a Block Plane works for the same job. I'm expecting it to take a little longer but also to have a slightly more precise finished product.

Riser is currently gluing onto the stave, I should be able to get in there tonight to trim & take a few pictures.

Scan of 'Book of the Bow' references attached also (third attachment heavily compressed to fit within the allowable size).

[Nezwin]

I've found that while my attempt was good, there are gaps in the glueline for the backing, a sign of my unfamiliarity with this method of preparation & room for improvement. Arguably, an epoxy would've filled these gaps (as opposed to the TBIII woodglue that I used) but it does highlight areas for improvement in my next build & where I need to focus my attention for next time. I found the beltsander to be good for quick removal of material but it also lead to some uneven results (edge to edge), so next time I'll see how well a Block Plane works for the same job. I'm expecting it to take a little longer but also to have a slightly more precise finished product.

Good gluelines shown here-

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Poor flattening job here -

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These are the only three sections where this has happened, so if there's a failure in any of those areas, I'll know it's because of that. I just hope they're not a deal breaker...

Whole bow pics -

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I've lightly sanded the bamboo by hand, removing the outer layer of dye & 'rind' (as I've seen it referred to elsewhere). There's still a bit to do there, though. I cut the fades quickly but haven't had time to tidy them up (3" fades on a 14" riser). Given that it's not been shot in just yet and is made of bamboo & timber, I've some concern that it won't hold much of the reflex/deflex shape, but that one I'll leave down to experience mostly.

Once the tips & overlay are glued in I'll post a next update. I'm optimistically hopeful that, with the longer working limb & lack of poor tip wedges, the Blackbutt belly should be up to matching the bamboo backing.

[greybeard]

...I found the beltsander to be good for quick removal of material but it also lead to some uneven results (edge to edge), so next time I'll see how well a Block Plane works for the same job. I'm expecting it to take a little longer but also to have a slightly more precise finished product...These are the only three sections where this has happened, so if there's a failure in any of those areas, I'll know it's because of that. I just hope they're not a deal breaker...

I have found spoke shaves also work well with the bamboo.

Did you try using some small clamps to close the gaps? I have small blocks with a concave face which allows to apply some extra pressure on difficult edges.

All bamboos are not born equally so be aware of what you are buying. Moso and Madake are probably at the top of the list for bamboo.

Things to look for when buying bamboo are small symmetrical nodes and a straight profile between the nodes. Quality poles produce better back and belly laminations.

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Daryl.

[Nezwin]

To tie up this thread, I managed to get the bow to a point that it was on the tillering tree yesterday. It lifted a very small splinter on the bamboo backing, which I glued down, and after a bit of sanding today, I put it back on the tree. After an hour of drawing, resting, then drawing a little further, I finally got it to 28" draw with a beautiful, quasi-symmetrical tiller, pulling about 37lb, which is approximately where I'd want it for a target bow.

All good until this happened -

Back

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Belly

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The limb that didn't lift a splinter yesterday failed in the most fantastic & dramatic way. I spent a few minutes looking for the tip, only to find it wedged under the insulation on the tin roof of the veranda.

Where did the limb go.JPG (154.37 KiB) Viewed 3032 times

From inspecting the failure, it struck me that this wasn't my fault (insofar as, it wasn't my workmanship that led to this but rather my choice of materials). This was a good thing. It seems pretty obvious now that Blackbutt just isn't a good timber to pair with bamboo. It's not overly clear, but the fracture seemed to be longitudinal and follows the grain.

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It looks to me like the grain in Blackbutt just won't take the compression from the bamboo. Even where there was no failure, it wasn't looking too great.

the grain did not like that compression.jpg (120.63 KiB) Viewed 3032 times

Prior to working the limbs, this was sanded very smooth. It's not clear from the image, but the grain has lifted a little, which appears to be the start of compression fractures throughout the entire limb.

So I take two things away from this -

1. Blackbutt might make a selfbow, or a cloth backed bow, but it doesn't play well with bamboo.

2. Failure did not occur where I had not properly flattened the bamboo, so that was not a great factor in this. Incidentally, I prepped another bamboo backing which is looking like it has avoided the side to side issues in this bow and I remain optimistic it will work, eventually...

[bigbob]

Perseverance may be the name of the game but patience is one hell of a virtue! Hope you get an agreeable result form the next attempt! Blackbutt sure seems like it doesn't add up to great material in such a configuration.

[hunterguy1991]

The "lifted" grain you posted the image of is due to moisture... When you sand timber very smooth then leave it sit for long periods without a seal of some kind the humidity will have an effect on the outer layer of wood fibres causing them to swell...

I have had timber do the exact same thing up here in Qld where its very humid. Hickory is particularly noticeable even if only left overnight after its sanded smooth.

If there is a Masters anywhere near you it might be worth trying some Red Oak or Spotted gum as a belly lamination. If you choose spotted gum look for a piece that's darker in colour rather than light and more orange, and also with having tight grain.

As Daryl said, theres a lot of trial and error in it so keep at it and you'll get a shooter.

Looking forward to seeing the next one from you as I'm also just about to start playing around with some pole bamboo as a backing.

Colin