Saturday, 21 February 2015

Two Steps Forward One Step Back

The Bamboo backed Yew longbow has gone back a step while I heat treat the belly. I removed the handle block, not without some poor decision making in the process. (Note to self... use bandsaw not chisel!)
It had taken the merest hint of set over the middle of the bow (just 1/8" or so) so I clamped it down with about 1/8" of reflex mid bow just to pull out the set whilst heat treating it.

The main reason for removing the grip block was so that I could get the heat treating right in under the grip, but keeping it off the actual splice. I taped a thin off-cut of Yew over the glue area of the splice and carefully clamped slats of wood to the sides of the bow to keep the heat onto the belly and off the splice.
Anyhow, that was all done and a new thinner longer handle fade block glued on. That's nicely cured this morning, and I'll add another thin build up block for the grip today.
The result of all this messing about is the bow should be substantially stiffer in the centre section and have a more gentle fade from limb to handle. It should make the 50# at 28" that I wanted.
All a lot of work, but I've learnt some new stuff about heat treating backed bows and lateral correction. Someone has asked what glue I use to survive the heat treating... the whole point is you keep the heat away from the glue line... but for the record I use Resintite.
I've added the diagram to show how the side cheeks keep the heat off the glue line and back. The great thing about this set up is that the heat is directed along the channel formed by the side cheeks and gives a more even heat over a longer area, this also speeds up the proccess. You can feel the hot air blowing out at either end of the channel showing that it is going where you actually want it. (in the diagram, Orange is the belly, Yellow the backing and blue the side cheeks, these are clamped on with G clamps)

While I was in a gluing frame of mind I made a former for the RD Bamboo backed Yew flight bow.
It was sawn from 3/4" ply, done as two halves and screwed together with a couple of side cheeks at the join. Blimey what a struggle clamping and binding it to shape, a bit like wrestling a Python. I didn't go mad with the reflex and opted for gentle curves as I didn't want to risk fracturing the belly as it pulled into shape.
The Bamboo backing was taped onto the belly with masking tape to hold 'em together while I strapped it up (visible in the lower pic), a few temporary clamps were applied too.
I had to cut a whole load of extra rubber strapping and I was tired out by the time I'd got it all done, I was also dying for a pee, hungry and wanted to blow my nose.
Once I'd seen to those minor distractions I thought I'll take a pic for the blog... Good call.

It really shows the value of the blog as, while taking the pic I noticed the alignment was all to hell!
The former is rather long and only of 3/4" ply so it has little resistance to sideways bend or twist. The force applied to the rubber strapping had put in about 1/2" of sideways misalignment and a bit of twist.
The glue has a good long pot life of a couple of hours, so it wasn't a problem to fix a clamp to the bench and to pull one end across and into line. A sash cramp at the other end was supported and blocked up to take out the twist.
Whew, what a relief... if I hadn't spotted that, I'd have been struggling to re-align and de-twist the bow.


  1. What kind of glue are you using for backing that can survive heat treating? I've had some rather disastrous results mixing heat and glue...

  2. I've added a note and a diagram to clarify.
    Note, I wouldn't try this with a bow that had multiple laminations. I think it's fine with a simple backed bow. I'll post a pic of the set up I used to make a slight correction to the RD Boo backed Yew flight bow on my next post.