how not to recurve tips

[Innocente]

so i decided to recurve a red oak build i'm doing, having seen it in several buildalongs on the various bowyer sites.

this is the technique i used:
roughed out the board, glued on a handle, got it to the stage where i'd normally back it, right before i put it on the tillering tree.

steamed one tip over a boiling pot covered with aluminum foil for an hour.

took it out of the steam, put it aside for 15 minutes while i erected a series of blocks screwed to my worktop to hold the bow and the recurved end in place.

slotted the bow, gave it several bends of increasing force.

got disappointed by how little recurve i saw in my tip, decided that if wet heat failed, advance to dry heat. applied 1-2 min of 1000 degree heat from a heatgun, while continuing to flex the tip.

withdrew dry heat, noticed numerous fractures where the heat had been applied.  

apparently i made a series of mistakes on this one:  
1.  immediately flex the tip after taking it out of heat
2.  leave it in flexed position for a day? (not sure how long to leave it in flex)
3.  only ONE application of flex, not the 20 or so that i used
4.  complete cooldown of the wood back to room temperature before trying heating then flexing again.

i searched the sites after the failure, found this site:    bending wood with heat    which enumerated my many errors for me.

took a buncha pics to post, but the breaks are really hard to see, so not worthwhile posting em. the one positive: the final recurve, minus the break, was GREAT!  the bow was 68", and i'm gonna have to hack off 4 inches from each limb, so it looks like my boys are gonna get another bow.  not a total loss.

Just a post to point out how not to do it, for any newbies like me thinking of flipping the tips on their next build.

[4est trekker]

Two questions:

1) Did you take the wood from the steam, set it aside fro 15 minutes, and THEN try to bend it?  If so, that's the reason you got so little bend (or any at all, for that matter.)  Steamed wood needs to be bent immediately after taking it from the "steam bath."  With red oak I've found I have about a 20-30 second window MAX to get the board clamped and/or secured to ensure it takes the form and doesn't fracture.  Generally, I move like my butt's on fire and get the sucker bending as quickly as possible.  Again, maybe I misread your order of operation.  Using a backing strap on the convex side of the bend also helps to prevent fractures and allows you to bend the wood a little more quickly.

2) Did you apply the heat gun shortly after attempting to steam the bow?  If so, this is most likely what caused the fractures.  The moisture driven into the wood by steaming expanded and vaporized so quickly under the intense heat that it fractured the wood in order to escape.  It's kind of like when popcorn pops. The moisture in the kernel gets hot, expands, and then fractures the kernel.

In regards to your observed mistakes:

1) Correct!  Although by heat, I assume you mean steam?

2) When I steam wood I leave it clamped/secured in the form until the wood feels dry and cool to the touch.  However, I'm impatient, and it certainly does not hurt it one bit to leave it clamped longer.  I just get antsy.  However, you don't want to stress/flex the wood for several days after steaming and bending it in order to allow the moisture content to equalize.  Otherwise you'll induce extreme set and probably pull the bend out of the wood.

3) Yep!  Especially with steam.  It plasticizes the wood's cells, and the fewer times you steam it the better chance it'll hold its shape and retain its structural integrity.

4) Wait several days, not just until the wood is cool.  (Again, longer is better.)  You have to let ALL of the excess moisture driven into the wood through steaming escape.  Otherwise you'll still run the risk of fracturing it.  The equal and opposite is true when using dry heat.  You've got to let the wood set for a good number of days, only this time to allow the moisture driven OUT by the heat to return to the wood.  

Others will have more to say about this, and will probably offer better and more correct advice.  This is just what I've learned from screwing up a lot and then reading the right     books and articles!

[Innocente]

hey 4est trekker

thanks - your explanation of WHY to wait a good long time after steaming wood is especially useful.  
how long would you wait after applying DRY heat and bending?

[Ricker]

4est trekker nailed it so precisely there is no reason for someone else to chime in here...so don't think nobody wants to help you, h gave you all the info.
Cheers, and good luck

[Innocente]

whoops yer right chupa...didn't read the 2nd half of what he wrote...after dry heat ALSO WAIT SEVERAL DAYS for the moisture to return.
did a good job reading the first part, somehow missed that second part.

i WILL master this tip flipping.

[4est trekker]

The easiest (and most expensive) way to tell when wood is ready is to use a quality moisture meter.  There's an inexpensive shortcut, however, and it's outlined in The Traditional Bowyer's Bibles.  Get yourself either a postage scale or kitchen scale.  It can be digital or manual, as long as it reads in grams and has a high enough threshold to measure the weight of your bow.  Most scales go up to five pounds, so you should be okay there (I hope!)  Also, I say grams because 1) I'm a metric system convert, and 2) It's a much smaller, and therefore more accurate unit than ounces.  You can get them anywhere, including Target and Wal-Mart

Okay, here's what you do.  Once you've got your wood steamed, cooked, boiled, sauteed, roasted, broiled, fried, or whatever, let it sit for 24 hours in a horizontal position.  I say horizontal because you're trying to equalize the moisture content, and that can vary from floor to ceiling.  24 hours after cooking the wood, weigh it and record the number.  24 hours do the same thing.  Your number should change each day, going up if you've used dry heat, and going down if you've steamed/boiled it.

Now, when the number reads the same for two (preferably three) days in a row, you know that it's reached a stable moisture content and should be safe to work with.  Yet you must take into account your environment.  If you live in an extremely dry or humid climate/season, you need to take that into consideration.  

Hope this helps!  $15 on a kitchen or postage scale beats $100+ for a quality moisture meter.  By the way, I bought one of the $20 jobbies and it's not accurate enough for bow building.  Now, if you're REALLY impatient like me, you could always do a glue-on recurve tip since you're working with board staves.  You can look through the build-along titled "The 'So You Wanna Build a Bow' Build-Along" to learn how.  I like it because you can have a shooting recurve in 24 hours (the time it take for Titebond III to cure).  If you're wanting to try this and don't think the curves in the build-along is sever enough for you, let me know and I'll show you a way to get them bigger.

[Innocente]

slick, i'll go find me a drug dealing scale, with milligram increments.  i read so much about how when and why to heat treat on this site, i definitely wanna try it.

i saw that buildalong, thinking of testing it out on ol faithful, a red oak board.

thanks 4est

[4est trekker]

The milligram scale will be perfect, as the wood won't change very much as it dries out/rehydrates.  It's a really slick method to use when checking the stability of a stave, as the wood will loose a lot of weight on it's transition from green to seasoned.  Nonetheless, you can use the same technique here with some success. Good luck!