Friday, 19 August 2016

Very Interesting!

The Wonky Hazel now has a string and it shoots where you point it...
But the arrows waggle viciously from side to side!?? (See pic, accurate, but arrows sticking in at odd angle.)
I increased the brace height and relieved the arrow pass a tad, no real difference.
I'd noticed that they flew smoother from a higher position where the grip swells back out towards the limb.
Maybe the arrow pass is too close to (or even beyond) centre shot?
In true scientific fashion, having formed a hypothesis we must test it.
I took a scrap of wood about 3/16" thick from the scrap pile and taped it onto the arrow pass with some masking tape. Perfect arrow flight! Hypothesis proved.
So what's the fix? As usual there are multiple possibilities.
1. Heat bend at the grip to correct the string line.
2. Glue on a sliver of Hazel to the side of the grip.
3. Add a thick chunk of Waterbuffalo horn as an arrow plate.
Well 2 and 3 are a rather poor last resort type fix, I'll jig it up for some steaming of the grip, same as last time (see pics) but a bit more.
Thinking about it, if I want to move the middle of the bow over by 3/16" then I need to move the tip over by twice that, 3/8" which is a fair shift when all the bend is at the relatively thick grip. I've jigged it up and filled the steamer right up with water so it's had about an hour steaming.I must resist the temptation to un-clamp it until tomorrow morning. Note:- In the pic above, once it had about half hour steam I tightened the clamp with the yellow jaws to pull the limb nearest the camera right across to the wooden jig.

Once again this illustrates the difference between a bow, and a good bow. Having had this minor set back it was nice to get an E-mail from a mate of mine for whom I'd made a new bamboo backed Yew longbow.
"...thank you for the bow which is without doubt the best I have ever owned.
It’s light to carry and being only 40lb at last I am anchoring properly but despite it lightness it’s as fast as  bows I have owned with heavier poundage."

Update:- When I unclamped the bow the tip had moved across about an inch and a half! Oh dear, have I over done it? No, give it an hour to relax and it's already moved back a good deal. I'll leave it all day and see where it finishes up. Heat bending can be V tricky, sometimes heat treating ( getting up to about 200 degrees C) will help fix a bend in place as it stiffens and hardens the wood.
Update 2:- 8 Hours later it seems to have stopped moving, I've strung and shot it, clean and true arrow flight.

Explain more... I'm not sure which bit, but I'll assume the arrow flight.
Without a high speed camera I can't be sure what's happening but I have my experience to go on, so I'll go through my thought process.
Here's the stuff I know

1. The string line was a bit to the left, known from having made the bow.
2. 45# @ 28" draw weight, length and brace height about 5".

3. experience tells me my arrows suit a bow of that draw weight, length and brace height so should fly straight.

Experience tells me that generally arrows waggle when they are too weak spine, the arrow pass is too far left (e.g The arrow has to bend a long way to get round the bow).
I normally find that moving the arrow pass towards the centre line and/or raising brace height improves things... it didn't this time.
I've found that over a lifetime in electronics design and in other things that sometimes the answer is in the opposite direction to what you expect! So I had the theory that the arrow pass was too close to centre rather than too far away. My experiment proved this to be the case.
But it begs the question how can it be too close? Surely centre shot is ideal? Well you'd think so, but modern target recurves have a pressure button to give fine adjustment and they are generally slightly less than centre shot.
Why? ... My guess is that as the string slips off the fingers and initiates some lateral movement the arrow is normally forced against the side of the bow, if it is cut away too far the arrow can come away from the side of the bow an there is no friction to damp out or constrain it's oscillation. Put simply, it has too much room to waggle!
This theory is supported by my observations with the flight bow a few weeks ago where I had two arrows smash during loose, the addition of some stiff bristles from a brush prevented it.

Hope that extra explanation is some help.


  1. Hi Del , I used to spot steam a section like you do , until I had a conversation with an old friend who makes walking sticks .
    He recommended wrapping the section with a wet(damp) cloth ( I use a facecloth size of an old towel wet and wrung out) and then wrapping that in tin foil. then just heat it with the heat gun .
    Its a lot less messy and can be a lot more specific . If the foil is well sealed all steam gets forced into the wood reducing the time needed to steam . It also means you don't have to be as specific where you add the clamping force as the steam point is the weak point
    It was a light bulb moment for me - hope it helps :-)

    1. Cheers, I'll have to try that, but it's prob only good on small cross sections. A walking stick is a bit slimmer than a bow grip.