Wood bows and the Australian Climate

[Brumbies Country]

I was shooting with a friend Sunday and his Osage Elb broke. You really feel for somebody in those circumstances. Nice looking bow, he'd put alot of work into it and was shooting it well. We talked about the dryness and heat (low thirties that day) of the climate. I know we can expect a reasonable percentage of self bows and laminated wood bows to break but I thought I'd get a few opinions on their relative fragility under Australian conditions, bearing in mind that while it is hot with low humidity down our way currently, in much of Queensland it is hot with very high humidity.

Can we expect more string follow and increased fragility in self bows as the temperature rises? Would this be less with Australian native timbers as opposed to Yew, Osage, and imported Ash for example? Is there danger in leaving an unstrung selfbow in the car at this time of year? How much does high temperature effect arrow speed in a self bow, or laminated wood bow? Is a relatively high humidity better for a wood bow?

These questions were prompted in part by the broken bow but also in part by Grahame's January longbow footage from the UK. You'd have to think the temperate climate where wood bows originated suits them (and the materials were readily available) and contrastingly the Eastern use of horn and sinew in shorter bows though this was likely dictated by ability to shoot from horseback and importantly, availability of materials.

The inclusion of fibreglass of course gets round alot of these problems but this is not at the centre of my question.

Simon

[longbow steve]

Hi Simon, good question. A bow should remain fairly stable if sealed properly but if it has spent time in the car at high temps I am sure it would start to lose moisture.
I have regularly put my bamboo lam bow in the hotbox at 60 degrees overnight after shooting in the rain, at times I have strung it and shot it with no apparent effect on its shootability whilst it is still hot.
I know Hickory would be a good choice for low humidity regions as it likes a low moisture content and palm wood bows from New Guinea may suffer without the humidity so there is definately somthing worth questioning there.
I look forward to responses from others who know more about wood bows. Steve

[Brumbies Country]

Thanks Steve

That's valuable input. Interesting your experiences re the laminated bow's shootibility post hotbox and good to know there was no apparent effect on shootability. Some of the comment re different woods should be interesting.

Cheers

Simon

[longbowinfected]

Very interesting.

The wide range of climates / temperatures / humidity levels across Oz would match most scenarios that exist now or that which will happen as and when the earth warms or cools. Are there any differences in the rate of failures comparing hot parts of Oz to cooler parts? Are there differences in each comparing softwood to hardwood exotic to native? I would respectfully suggest that the greater variability is not going to be climate based but lies within the natural variability in the raw product and further compounded by the ability, knowledge and processes and procedures brought to bare. Even in medieval times longbows were made in their millions as well as arrows in various grades but with the recognition that they were expendable....they always had three times more spare bows than archers in the baggage train for a 4-6 month campaign. The bowyers here across Oz and elsewhere could give us a practical insight, especially the technocrats like Len, Darryl, GA, GK, Steve Farrell. Then you talk to the really excellent accurate archers but because they make successful micro adjustments without thinking about it you have to turn to the less talented archers, we take more arrows to effect change therefore notice these events more.
A case in point: shooting across water with a 40# bow the imber arrow drops lower than normal because of the slowing effect caused by water vapour from evaporation from the water....over 40 metres it can be a half target difference.

The reason timber was not used in India, and in the middle east was partially because of the effects of dry rot, wood decay fungi and termites being rampant. With the horse warrior nations they did not stay in one place long enough as well and used resources from their mobile herds. The Indians used steel.

Wood is wood and timber is timber....wonderful but not perfect. No two pieces of the same species are the same; no two sections from the same piece are the same chemically, structurally or by any other means of comparison.

Putting temperature aside other than high temperature in a car is going to get up to 80 degrees and it must cause problems. If you leave a number of bows in the sun even under shade during normal use the colour changes...change is taking place both chemically and structurally in front of your eyes.
This can be controlled by behaviour and the way you store/use your bows.

Changes in local or other moisture levels in atmosphere are quite different and this can vary the level of moisture in properly seasoned timber/wood and vary from 8% ish for dry areas up to 12-15% coastal and even higher in tropical areas. This can be controlled by careful harvesting, storage, manufacturing, sealing and oiling over the life of the bow....ask GK he goes to extreme [and proper lengths] to control moisture loss/gain over time.

I notice that my ow takes about 15-30 full drawn shots to warm up.... fewer in warmer weather, more in cooler weather...at that point I need to adjust my aim. Timber also relaxes after being under strain, so it is in its nature to be variable.......do loop back up to the top.

We should be allowed to place a butt 5 metres away and warm up our bows and timber arrows before shooting practice ends...good way to warm our muscles up too. We should make 12 volt electric blanket bow bags to warm our bows and timber arrows up gently on the way to tournaments / shoots.

Kevin

[Brumbies Country]

Very interesting.

The wide range of climates / temperatures / humidity levels across Oz would match most scenarios that exist now or that which will happen as and when the earth warms or cools. Are there any differences in the rate of failures comparing hot parts of Oz to cooler parts? Are there differences in each comparing softwood to hardwood exotic to native? I would respectfully suggest that the greater variability is not going to be climate based but lies within the natural variability in the raw product and further compounded by the ability, knowledge and processes and procedures brought to bare. Even in medieval times longbows were made in their millions as well as arrows in various grades but with the recognition that they were expendable....they always had three times more spare bows than archers in the baggage train for a 4-6 month campaign. The bowyers here across Oz and elsewhere could give us a practical insight, especially the technocrats like Len, Darryl, GA, GK, Steve Farrell. Then you talk to the really excellent accurate archers but because they make successful micro adjustments without thinking about it you have to turn to the less talented archers, we take more arrows to effect change therefore notice these events more.
A case in point: shooting across water with a 40# bow the imber arrow drops lower than normal because of the slowing effect caused by water vapour from evaporation from the water....over 40 metres it can be a half target difference.

The reason timber was not used in India, and in the middle east was partially because of the effects of dry rot, wood decay fungi and termites being rampant. With the horse warrior nations they did not stay in one place long enough as well and used resources from their mobile herds. The Indians used steel.

Wood is wood and timber is timber....wonderful but not perfect. No two pieces of the same species are the same; no two sections from the same piece are the same chemically, structurally or by any other means of comparison.

Putting temperature aside other than high temperature in a car is going to get up to 80 degrees and it must cause problems. If you leave a number of bows in the sun even under shade during normal use the colour changes...change is taking place both chemically and structurally in front of your eyes.
This can be controlled by behaviour and the way you store/use your bows.

Changes in local or other moisture levels in atmosphere are quite different and this can vary the level of moisture in properly seasoned timber/wood and vary from 8% ish for dry areas up to 12-15% coastal and even higher in tropical areas. This can be controlled by careful harvesting, storage, manufacturing, sealing and oiling over the life of the bow....ask GK he goes to extreme [and proper lengths] to control moisture loss/gain over time.

I notice that my ow takes about 15-30 full drawn shots to warm up.... fewer in warmer weather, more in cooler weather...at that point I need to adjust my aim. Timber also relaxes after being under strain, so it is in its nature to be variable.......do loop back up to the top.

We should be allowed to place a butt 5 metres away and warm up our bows and timber arrows before shooting practice ends...good way to warm our muscles up too. We should make 12 volt electric blanket bow bags to warm our bows and timber arrows up gently on the way to tournaments / shoots.

Kevin

Thanks Kevin

There's some very interesting reasoning in here and with your background in timbers i was hoping that you would reply. I took particular note of your comments re "natural variability in the raw product and further compounded by the ability, knowledge and processes and procedures brought to bare." Appreciate your point about variation species to species and within pieces of the same species. Really interested in your comments re shooting across water. In a lot of reading and listening I'd not come across that before and it makes a lot of sense.

The need to warm up a bow really came home to me shooting in the Snowies in cold early morning temperatures. I normally religiously shoot quite a few arrows in practice. I didn't this day and the early results were catastrophic using a selfbow. I havent noticed that so much with a laminated fibreglass bow.

Re your comments about bows being a disposable item I intend using that to good effect in justifying an increasing number of bows to Ainslie .

Simon

[Graeme K]

Hi Simon
I think all that appear above is true. But the simple answer is that bows of any wood are more likely to break at lower MC and will take more set at higher MC.
Obviously some woods are more critical at low MC than others but the local timbers show the same range of susceptibility that imported ones do.
In the case of the Osage bow you mentioned it is unlikely that either elevated ambient temp or the reduced MC was the direct cause of the failure since osage is fairly tolerant of low MC and high 30 temps should not be a problem for the wood. The reduced MC would only become a factor if the bow was under built and highly stressed to begin with which is something I can not comment on having not seen it.

I think the important thing to remember here is that all self bows only have a finite life -- in other words if used continually they will all break as a result of that usage. When they break will depend on how highly they are stressed -- which varies with MC, design and material and may number from a few hundred shots to many thousands but in the end they will all break.

So it is no use being surprised that a wooden bow has broken or thinking that something must have gone wrong for it to have happened since it is just the nature of the beast and all those contributing factors are just variables which dictate when that end will be.

Graeme

[longbowinfected]

Fair enough,

but having said that about elbs the modern glassed flatbow/longbow is a pretty durable piece of equipment.....I have seen them dropped onto rocks, dry fired and still go ok.....modern compounds and recurves are not as tough in my opinion.

Bloody good thoughtline you brought up.

Kevin

[Brumbies Country]

Thanks Graeme

That's really good information and I hadn't read anywhere before that bows are more likely to break with a lower MC and will take more set at higher MC. Bit of a sobering thought that all self bows have a finite life and given that I am really enjoying shooting this selfbow that will spur me on to build a reserve. I have a quick question in relation to that: Will wood laminations likely increase the life of a wood bow on average, or will that again vary with MC, design and material?

Simon

[longbowinfected]

laminations and even cloth or other backing help....look at all the laminated veneer lumber i beams etc around doing what used to be done by steel....having said that you do not want differentmc in each lamination and they have to be compatable or if there is a geat difference in their elasticity and how they bend, how they accept the binding agents etc the laminations work against themselves. The real bowyers / technologists like GK, GA et alia can give you the best advice on what goes with what.

Make bows in pairs when you make selfbows and hope your mate does not nick it.

Kevin

[jape]

Coincidentally I was just about to post a photo of my longbow with the same question of MC, so will piggy-back in your thread if you don't mind Simon. This is a pic of what has happened over last two days, a warp of the limb occurring directly from the point it is not supported on the dresser top, the rest of the bow remains very flat, no follow or bend. It has been kept up there for two years through summer and winter with no effect. It is boo back and probably iron-bark belly (I can't remember). It is used quite often and has always been stable until these last two days of extra heat in Victoria. But what got it was the air-con not the heat! It was kept at 21 degrees while outside was 40+. I thought air-conditioning dries the air though, so was going to ask if removal of MC would warp it like this, but this thread suggests that added MC would cause set. I am confused.
I will leave it a few days to see if it comes back naturally, if not I will suspend a weight from it and if that doesn't work I will get more drastic.

[Brumbies Country]

I agree that's a hard one to explain Jape. I think it is generally understood that airconditioning significantly lowers humidity (as opposed to evapourative cooling which would slightly increase it) and therefore MC could be lower if sealing of the bow allowed some moisture loss. I guess my uninformed mind would wonder if this is following some previous stress, though you'd reckon the bow would have had to have been shot recently for that to occur.

Simon

[Graeme K]

Hi Jape
No idea why the bow would change shape while unstrung -- the deal with MC affecting the durability/stability is only a consideration if the bow is strung and/or drawn.
The only explanation I can think of for your bow is that the end that has changed shape has expanded or contracted by different amounts in the two laminates -- dont have a good explanation for this.
Hi Simon
All wood laminated bows tend to be more stable than self bows but still break if the MC gets down to dangerously low levels. There does not seem to be much trouble with combination of different woods because regardless of the strength characteristics at different MC all woods stabilize at the same MC in the same ambient conditions -- I suspect that the rate of change may be different in different timbers but the magnitude of this does not seem to cause internal stress or delamination -- this is why I find the above scenario difficult to explain.

Graeme

[jape]

I guess my uninformed mind would wonder if this is following some previous stress, though you'd reckon the bow would have had to have been shot recently for that to occur.
Simon

Actually that is very close to the probable cause Simon, thanks, the bow originally took a bad set like this on one limb when first purchased, but I straightened it and did some other work, trapping, re-handling, re-gluing to get it more efficient and usable. Then painted and sealed with varnish. That was more than a year ago though and it has been used a lot since and been through the cycle of seasons without any movement at all. It was last used a fortnight or so ago - but this set definitely took place over the last couple of days. Strange how it warped up directly from the point where it is exposed and unsupported. The aircon is a portable unit but is dry refrigerative aircon, not evaporative. Just possible that hotter air was sitting in that corner above the bow but I doubt the differential would have been more than a couple of degrees. Hopefully someone else will have a suggestion as that will direct how I re-align it. I was thinking of heat and clamps to force a d/r recurve (both limbs) as Dennis LaV once posted about to fix string follow.

Thanks Graeme, I hadn't understood you were talking about unstrung bows, this was just sitting flat as it always has. I shall leave it for a couple of days then shoot it and we shall see. No sign of delamination or glue problems, no cracks to the paint or varnish.

[Brumbies Country]

Hi Simon
All wood laminated bows tend to be more stable than self bows but still break if the MC gets down to dangerously low levels. There does not seem to be much trouble with combination of different woods because regardless of the strength characteristics at different MC all woods stabilize at the same MC in the same ambient conditions -- I suspect that the rate of change may be different in different timbers but the magnitude of this does not seem to cause internal stress or delamination -- this is why I find the above scenario difficult to explain.

Graeme

Thanks Graeme

Really appreciate that reply and it does move one to think about a laminated wood bow if looking for longevity.

Simon

[jape]

There does not seem to be much trouble with combination of different woods because regardless of the strength characteristics at different MC all woods stabilize at the same MC in the same ambient conditions
Graeme

That's rather interesting, I would certainly have expected different woods to stabilise differently because of cell shape, structure, density, grain and so on. Maybe it is a property of cellulose itself rather than related to structure then? However even then you would get different resins and oils I would have thought. Just realised I know a lot less about wood properties than I thought!

[Len]

Great topic Simon, thanks for bringing it up. Graeme is right on the money in regards self bows not lasting for ever.Actually they may last forever but not at the same level of peformance unless hugely over built at the cost of performance.
I know with my own bows they will deffinitely follow the string more after shooting a lot of arrows on hot days ( 30+ ) but because of the heat I reckon you could probably gently push them back ? I haven't really tried this but would be interested to hear from the more experienced bowyers on this idea. Generally what I do is de-string them at any lengthy break in shooting and try and keep them in the shade between ends and that way they don't seem to be that affected.

[Brumbies Country]

Thanks Len

I'm really enjoying shooting the bow. I shot at about 36 degrees last evening and just wondered if there might be a bit more string follow. At the moment given the daylight hours I'm trying to shoot some arrows most days. I'll try your recommendation of very gently pushing the limbs back. Most of my shooting is done in the shade at home or one of two field courses where there are plenty of trees so there is not much exposure to the direct heat of the sun.

I nearly posted a month ago, noting all the great bows that people are making, and with the intention of asking what happens to them. Following Graeme's post I think I know the answer .

Simon

[GrahameA]

Evening all

My experience indicates that it the average moisture content of the air that is the main factor in the wood moisture content. Put it in a low R.H. enviroment and the moisture content will go down and the timber will move )shrink). Put it a high R.H. environment and the timber will move (swell).

Timber that has a very low Moisture content is brittle.

Moisture will migrate across many membranes - including acrylic sealants.

Addenda

Hi Jape
No idea why the bow would change shape while unstrung -- the deal with MC affecting the durability/stability is only a consideration if the bow is strung and/or drawn.
The only explanation I can think of for your bow is that the end that has changed shape has expanded or contracted by different amounts in the two laminates -- dont have a good explanation for this.
Hi Simon

I would start looking at the airflow across the overhanging section compare to the air flow on the top of the cupboard.

You may well discover that the moving air is changing the moisture faster that the rest of the bow.

[longbow steve]

With regards to string follow, My straight laid bamboo longbows follow the string by about 1/2" after being shot in and at the end of a days shooting 3/4" is visible. You may have read about Howard Hills stringfollow bows and how stable forgiving and accurate they are some even feel the need to induce srtingfollow when constructing the bow???? All they need to do is get the bow working down towards the riser rather than outer limb. Sorry to go off track. Steve

[Brumbies Country]

With regards to string follow, My straight laid bamboo longbows follow the string by about 1/2" after being shot in and at the end of a days shooting 3/4" is visible. You may have read about Howard Hills stringfollow bows and how stable forgiving and accurate they are some even feel the need to induce srtingfollow when constructing the bow???? All they need to do is get the bow working down towards the riser rather than outer limb. Sorry to go off track. Steve

Not off the track at all Steve. I think once you start shooting selfbows, and because stringfollow gets a bit of a mention in the literature, you become concious of looking for it. You mentioned the 1/2" after being shot in and at the end of a days shooting 3/4" being visible. Just wondered if you were implying that there was some return after rest. I mentioned that I thought I saw a very small increase in string follow after shooting at 36 degrees the other evening and I couldn't see that increase when I looked last night. Having said that it was all pretty subjective and I didn't physically measure the difference .

Simon

[jape]

Addenda
I would start looking at the airflow across the overhanging section compare to the air flow on the top of the cupboard. You may well discover that the moving air is changing the moisture faster that the rest of the bow.

Observation would say that may be correct as it has warped upwards from the point it is overhanging, and the fan on the aircon would have been moving the air continuously but slowly over two days. You could certainly feel a difference when standing up as opposed to seated (or sprawled on the couch). I wonder if all the glass bottles on top of the dresser kept it even cooler there and the warmer air in the room funneled through that corner? A strange phenomenon whatever it was. So, I imagine it was the ironbark contracting more than the boo from drying out? No sign anywhere of creases in wood or cracks in varnish. As the temperature and moisture content has returned to normal it has come back about a third the amount, half an inch. It will be stored in another room on the east side that is less affected by changes in the temperature despite being unheated and not cooled - after I have straightened it out.

This whole thing would suggest that a difference in temperature of a few degrees and an large change in ambient MC can affect a bow laminated of differing materials quite drastically. I shouldn't think the fact that one is a grass and the other a timber would be all that relevant, (or would it?) Simon's original question was about increase in tempoerature and MC change, I think this shows that it is MC not temperature at all as cooler air can dry the atmosphere just as much.

[longbow steve]

Hi Simon, yes my bow recovers after rest to it's origional 1/2". I am sure if you took an out line or measure with a straight edge the set(string follow) of your longbow at rest and then after a days shoot it will be different but should recover back to origional otherwise we would see the set becoming greater every time we shoot the bow.
To me moderate string follow steming from the riser end of the limb says that I am asking the most of my materials and design for maximum performance. JMO Steve

[Brumbies Country]

Thanks Steve

That sounds to make a lot of sense. If I don't talk to you before, I hope you have a great Canberra shoot. I'll be in Orange, but a couple of us are hoping to make it to Wiseman's Ferry begining of May and hopefully I'll catch up with you there.

Cheers

Simon

[longbow steve]

Thanks, all the best with Orange Wisemans Ferry should be fun.
Steve

[longbowinfected]

With the bow resting partly in air, do not forget that hot air rises which means that by comparison with the larger mass of the wall unit that end will be cooler because there are more molecules to be heated to raise the overall temp. Not only that because of the riser being at rest it forms a "straight line" even though in reality it also would be set back. The combined effect would be to elevate the line of the limb making it appear more affected. Why not set up a pegboard with the silhouette marked out with the bow laid flat/parallel to the ground. Shoot the bow for different numbers of arrows in different conditions and measure/record the variances?

Timber is variable. Humidity in the air and in timber varies according to air pressure, elevation and temperature variations. Then you get variation in elasticity because of temperature and moisture content , mass varies so therefore movement is varied. If you work the bow it relaxes. If you hold for a long period of time your own muscles relax as well as the timber fibres. If you want to straighten a bent timber arrow you apply heat to the arrow by rubbing the round shaft up and down the arrow, it is called burnishing....heat/temperature and humidity are variables which effect a product with variable performance [timber].

Keep your bow oiled but not too much. Weigh your bow and keep it at the same mass and store it in a bag or tube at waist height not near the ceiling or in the roof or on the floor or in the subfloor. The higher you go the hotter, drier it gets; the lower you o the cooler and more moist it gets.

Do not place the pointy end of your bow on the ground; do not place/lie your bow on the ground and only ever store the bow in your car if the car is in the shade or your case is insulated.

Higher temperatures [much higher but still relevant in counterpoint] even affect carbon arrows and aluminium arrows and they are engineered products with very limited variability.

Kevin

[jape]

Thanks Kevin. The bow is flat on the top of the cupboard along the whole length until it kicks up from the overlap point on one side (top limb) only. It rests on two bamboo nodes, either side of the handle, which line up with the handle wrapping so it is flat at three points and quite horizontal overall and supported apart from the last foot or so one end, which is where it has warped. I would have expected string follow to take place over the whole limb length or at least from quite close to the handle.

It is not an optical illusion and I did measure it with a straight edge laid along the dresser top in the first place, at just a touch over 1 1/2 inches, now it is just a fraction over 1 inch. The bow sits there everyday after use as it has done for nearly two years and is in my direct line of sight from where I use this computer, that is how I first noticed the warp. I always place it in the same position within inches as otherwise I would knock it with my head as I walk past the other end which is by a doorway.

The only factor that has changed apart from usual gradual seasonal temperature/MC changes which have not affected it before, was the aircon used here for the first time. The ceiling height is from 9 foot to 10 foot 6 inches over a 46 square meter room so it isn't stored up in the hot spot of a small room. The bow is sealed with two coats acrylic paint but then shellac gloss varnish, at least two coats so it should have been quite moisture stable. The bow hardly ever gets shot more than a dozen or so arrows at a time and usually shows no set whatsoever.

But it isn't all that important to work it out I suppose, I just felt it added to Simon's thread and was an anomaly I could not explain.

[longbowinfected]

both you and Simon put up some very interesting stuff here. These sort of things teach us a lot, sometimes the lesson is we do not know enough. These sorts of threads are the sort of things that separate this website from others [along with other cool things] for mine......never ceases to amaze me the amount of science and technology involved in two pieces of timber and a string.

Kevin

[greybeard]

I can’t offer a technical solution to your demise.

The selfbows that I have made from air dried bush billets have always had several applications of Danish oil or similar rubbed into them. Every six months or so I rub the bows with a Scotch-Brite scourer or an un-soaped steel wool wad to remove grime and then rub in more oil.
When not being used they are stored in a padded bow sock in my garage/workshop. At worst the temperature would get to about 38 degrees.

The cellulose fibre in wood, being hygroscopic possibly absorbs the oil because most of the original moisture content of the wood has been lost during the drying process.
Perhaps the penetrating properties of the oil finishes inhibit the migration of moisture?

Acrylic finishes may provide some outer protection for the bow but do little for its inner well being.

When dealing with natural materials always expect the un-expected.

Daryl.

[jape]

It hasn't come back any more but still shoots fine even with just one limb out of line, not that my accuracy is good enough to tell what difference it has made! A dozen or so shots was all I could manage. Seems to be a louder string noise but that may be my imagination. Unfortunately it has returned to the original warp of inch and a half but this may settle again. I shall try to straighten it sometime by over-flexing the other way when I have finished all my many other accumulated jobs around the place.

I will strip back to bare wood and closely inspect under the paint/varnish, heat with hairdryer and use a weight on tip and clamp at fulcrum point. Which side should I heat do you think and would it help to soak it in water before bending and then allow it to dry under the weight? Sorry Simon, I didn't intend to take up so much of the thread.

[ichiban]

im not to sure about yew but osage should be fine in aus, as many of you know osage was imported by americans to act as wind breaks and they have survived.... as far as bows go from what i know oasage has a huge reputation for being almost unflappable in extreems as long as the bow is looked after. i remember reading about a guy in alaska who builds and shoots osage flat bows all year round. is it possable that the bow was not propperly warmed up prior to shooting??, i have heard however that yew is a bugger in climate changes.

i personaly think that the english used yew because it was there, the indians used osage because it was there we should be using more aussie trees cause they where made to deal with our climate.

just my ideas.
Dave