clamping wood into a deep form?

[Prarie Bowyer]

I'm working on a bamboo backed eucalyptus bow.  I decided to add a thin lam of maple into the mix for visual appeal.  My form is pretty deep.  So deep infact that I'm afraid to just cram the bow in.  I think I need to do something or it will break.  I thought about (1) Using a hair dryer and individually heating the laminations (there are 4) dry and pressing them in. (2) soaking them in boiling water.  The tips of each lamination are mostly pretapered to help.  Then clamping them into the form to dry.  (3) gently easing them into the form and clamp them like that over a period of days. 

I'm pretty positive that just stuffing them all in will break some of the laminations.  Possibly not if I were using all bamboo but I'm not.  The maple lam fits in fine.  The thinner Eucalyptus lams will work but two of the belly lams are a bit thicker and will break if I force them in dry and or cold. 

The form is made to ride with the back of the bow facing up.  This way I can use it for Bamboo or other types of bows.  Putting the bamboo crown down into the form would require modifying the form in a way that might make gluing nonbamboo problematic.

So which way would you recommend the preshape the wood to fit the deep reflex deflex form?

[Del the cat]

I'd say steam the thick lams. If you can make up a long enough steam chest or steam pipe, it's proabaly easier to get the whole lot hot at once that way, or a long hot box and get 'em up to about 150-200 C
I think trying to heat localised areas is harder to control, although having said that, I've done ok with a heat gun and aluminium foil wrapped around like a tube to direct the heat along where it's needed.
The first picture on this blog entry shows how I mean... http://bowyersdiary.blogspot.com/2011/08/better-bending-technique.html
Good luck
Del

[Prarie Bowyer]

Very helpful ! Thanks

[Lee Slikkers]

If you have a Steam tube I'd use that as my 1st choice.  I would also steam and place in the form to clamp separately as some woods have a tendency to bleed when steamed and can transfer those colors to any white or light colored wood (maple) etc.

If you don't have one they are cheap and easy to make for around $30 bucks.  Good luck~

[Pat B]

How deep is your form?  If you add too much reflex to a bow you can end up with more set because you are over stressing the wood.

[Prarie Bowyer]

Well it's for a 66" ntn bow.  Striking a verticle line across the "nose" of the center of the form the depth of the reflex is 3".  It's not evenly distributed but more of a hyperbola pushed towards the tips.  It isn't quite a true recurve but it's pretty deep.  However I've seen much deeper forms such as this one by Sam Harper (Poor Folks Bows).


From this form he has made several all wood recurves.

I can get a 1/4 piece of maple to fit into the form.  The same thickness of Eucalyptus will go about 3/4 of the way and then starts to sound a bit iffy.  I want to take the stress of the wood before the glue assembly.

[Stretch]

Luthiers and Shaker box builders will use a hot pipe or bending iron to spot bend wood.  There are all sorts of instructions for home made bending irons is you do a search.  One way is to drill and tap a normal clothes iron and bolt a pipe to the bottom of it.

I've had good luck pressing wood into bends as tight as yours (for furniture applications but not for bows) by soaking in water and pressing the wood into the form with a hot clothes iron.  For your application I would mark the middle of each piece and clamp it in the middle of the form.  I've also made a negative of the form to press wood into the form.  Just make sure you allow for the total thickness of your bow.  Using this method I steamed the wood strips in a steam pipe.  For furniture applications the rule of thumb is 1 hr of steaming per inch of thickness. 

[Ryano]

I use a heat gun myself. That is a pretty sharp bend you got there though....

[Pat B]

This bow is very remenescent of the Wilcox Dou-flex bows of the 1930s. There is a section in TBBIII about the dou-flex that might give you some insight.
  Have you done your homework as to what thickness for each lam or whether they should parrallel or tapered or using appropriate wood properties for the back, core and belly or are you just winging it? A lot more thought and experimentation should go into a radical bow style like this one...and not just the lay up but also the method of tillering once the bow is out of the form.
  I'm looking forward to your progress. Keep us all posted and keep the pics coming as you progress.

[Prarie Bowyer]

That isn't my form.  Mine is shallower than that but I know it can be done this way.  I cut teh eucalyptus into 3 seperate laminations and pre-tapered two.  Kinda, using a hand plane.  I figure since all laminations are the same wood I don't need perfect tapers.  I used the hair dryer.  I worked but on one side it lifted a fiber.  That fiber looks like it's just the edge.  I'll be triming that off and hoping for the best.  A het gun will be a near future purchase.  I think then I can work with thicker wood OR just resign myself to just using it for all bamboo bows.

Other laminations fit it fine it was the 1/4" one that gave me trouble.