Primitive Archer
Main Discussion Area => Bows => Topic started by: WillS on March 29, 2013, 03:35:46 pm
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Just wondering this, as I'm working on a funky piece of yew at the moment. I've had to use dry heat to take out propeller twist, and huge amounts of lateral bend. It's taken weeks to get it straight and it's still not quite there yet, but it also has a large amount of deflex that I'd like to get rid of.
Will too much heating weaken a bow, or is it ok provided enough time is left for it rehydrate and recover? I got a bit hasty in a couple of places and scorched the belly wood, but once it had been roughed out closer to bow dimensions any sign of discolouration has now gone. It looks fine apart from some lateral drying cracks which I'm not too worried about. I just don't want to blast it again to remove the deflex if it will permanently weaken the bow or make it brittle?
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Try steaming....in my experience steaming works much better with yew....MUCH better;-)
Cheers
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I've tried steaming, and just didn't like it. Too much faffing about getting pans of water ready and then the rush once it's hot to get it clamped... just takes too long. Plus steaming doesn't really do anything different to the wood, it still dries it out about the same amount from what I can tell. The only advantage is that you can't burn/scorch the wood. Thanks for the reply though, appreciate it! It's the actual limit of the wood that I'm wondering about, steam or dry heat I suppose.
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It is a hassle I suppose....I dont belive dry heat and steaming give the same results tho.
But as to your question....as long as you rehydrate and dont burn it...then I dont think there really is a limit. The wood itself will have a limit as to how far you can manipulate it....but small corrections should be no problem.
Cheers
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STeam allows you to bend the wood further than dry heat it also softens it and makes it easier to bend the longer you steam it the better
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Too much dry heat will char and weaken it right through.
It's hard to bend thick sections. Impatience is your worst enemy.
I think if you can clamp it or apply force to it while the steam is actually on it that's the best way, as it can then be left hor a good long time. Trying to get from steam chest to clamps can waste valuable heat.
If you are using dry heat then use Aluminium foil or somesuch to direct the airflow all around the area, else you can end up heating one side while the other is cold.
Think how long it takes to cook a chunk of meat into the middle... same with wood, the heat has to get right in.
Better to have 200 degrees for an hour than 400 degrees for half an hour. The wood only needs to be at 100 to bend, but it has to be at 100 all the way through, Steam is more controllable if you can create enough and build a steam chest around the clamped up bow.
Del
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Right, ok. Cheers for the info. I really need to find a way to set up a steam jig that I can use in situ. At the moment the only way I have is to hang it over pans of water then dash over to a jig, clamp it up and by that time its lost a large amount of the heat.
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A wall paper steamer is a good source of steam and fairly cheap.
Insulation board can be taped up as an improvised steam chest.
For small areas I use a 5Litre plastic container with holes cut in to push the bow through and a hole in the cap for the steam hose. I wrap a bit of old duvet over it to keep the heat in, and allow a hole for water to drain out.
If you put steaming into the search engine on my blog it shows the various set ups.
Del
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Boil it.
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Cheers Del, ill have a play with some things. I have loads of huge polystyrene boxes lying about that our frozen snake food comes in so I might use one of those!
Bryce, I would but in this particular situation most of the bending needs to be done right in the middle of the bow! Is there a trick to getting that area into boiling water?
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Not sure on yew but hickory will take at least two heavy heat treats. I thought I was going to cause the bow to fail. I haven't shot it much yet but so far it seems okay. It's kinda heavy draw too for width of limbs. I have read that yew can be a little fussy though.
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Cheers Del, ill have a play with some things. I have loads of huge polystyrene boxes lying about that our frozen snake food comes in so I might use one of those!
Bryce, I would but in this particular situation most of the bending needs to be done right in the middle of the bow! Is there a trick to getting that area into boiling water?
Good point lol
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The polystyrene sounds ideal for making a box round it. A nice removeable top section with a brick to hold it down (other heavy objects are also available*)
You could get it all jigged up, but not under tension, steam it for 1/2 hour take off the top section apply a load of clamping pressure and drop the lid back on.
Watch out for that steam tho' it's nasty stuff, and the real hot stuff is the stuff you can't see.
Could even do support it sideways and have a rope going down through a hole in the box with a rope and weight tied to it (the water would run out there too)
*Maybe Wiley Coyote would lend you an anvil ;)
Del
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One point worth mentioning is you said you have already corrected it with heat a few times. Well if you steam/heat the areas that have already been done the corrections will come out....
If it were me I would be using a full length form/caul and as many clamps and shims as needed. I would use a heatgun and heat treat the whole stave. This method will give you the most control by clamping it were needed.
As a side note I don't really think its worth trying to remove deflex (especially near the handle)as it has a habit of returning during tillering which can lead to problems.
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Good point from Mike about heat allowing the previous bends to spring back.
The upside of that effect id if you happen to overbend a correction, a little gentle heat can help it to relax back a tad.
Del
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Thanks guys for all the tips! I may have to leave it then as I hadn't taken into account any springback more heat would cause.
Sadly, the stave has one beautifully straight limb which didn't need touching, then dead in the middle of the handle area it developed 45 degrees of twist, 5 inches of deflex, and a long s-bend that took forever to heat out! I'd love to remove the deflex as 5 inches BEFORE it sees any tillering is just nasty but if removing it means meeting the twist and lateral bends again I might just go a bit crazy!
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Sounds like a mate to the yew bow I just finished. It fought me tooth and nail and still isnt dead aligned like I like them, but it shoots great. I used all the aformentioned methods, when it boiled down the best method for my situation was a splash of cooking oil on the kink then dry heat from 8" away for 30 minutes, on a caul. Then I placed a wedge in the low spot and over bent it about 40%, most stayed.
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Yep almost could be from the same tree by the sounds of it.
Although I love the look of perfectly clean, straight yew longbows (I'm not aversed to character bows by any means, but sometimes it's nice to have them straight!) it's kinda nice shooting a bow that just fought you the whole way. Real sense of achievement once it's done, and the odd remaining kinks or twist always remind me of how bad it was.